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Pathology

Oncogenes and tumor suppressors: added drive versus lost restraint

Distinguish oncogene activation from tumor suppressor loss, then apply RB1, TP53, RAS, BRCA, VHL, NF1/NF2 and fusion patterns to cancer cases.

Cancer genetics becomes easier when you ask one question first: did the alteration create an active growth signal, or did it disable a safeguard? After this lesson, you should be able to predict allele behavior, connect a driver alteration to its pathway, and distinguish inherited first-hit risk from the later tumor event.

Start with direction: added drive versus lost restraint

A proto-oncogene normally supports regulated growth, survival, or differentiation. An activating alteration can convert it into an oncogene. At the cellular level, one activated allele can be sufficient because the altered product supplies an abnormal positive signal. Point mutation, copy-number amplification, and gene rearrangement are common routes to this state. [1]

A tumor suppressor normally limits proliferation, preserves genome integrity, or restrains a signaling pathway. Cancer can be favored when enough suppressor function is lost. The classic cell-level pattern is recessive because the remaining normal allele can retain useful function, but the two-hit rule is a model rather than a requirement that every suppressor acquire exactly two sequence mutations. Deletion, loss of heterozygosity, epigenetic silencing, dominant-negative effects, and dosage sensitivity can change the pattern. [1] [2] [3]

Side-by-side comparison of oncogene activation through mutation, amplification, or rearrangement with tumor suppressor loss through inactivation, deletion, loss of heterozygosity, or epigenetic silencing.
Classify the functional direction first: oncogene activation adds positive signaling, while suppressor loss reduces protection. [1] [3] [4]
Read the alteration before memorizing the gene name
AlterationTypical directionExamplePredicted result
Activating point mutationAdded signalingKRASRAS remains active longer
AmplificationAdded signalingERBB2More HER2 receptor is produced
RearrangementAdded signalingBCR::ABL1Constitutive kinase signaling
Deletion or inactivating variantLost restraintRB1G1/S control is weakened

Use the table as a direction test. If a change makes a signaling protein active without its usual input, think oncogene activation. If the change abolishes checkpoint, repair, degradation, or inhibitory activity, think suppressor loss. This distinction is more reliable than assuming a mutation is activating or inactivating from the word mutation alone. [1]

Prediction exercise: KRAS cannot efficiently hydrolyze GTP

RAS stays in its active GTP-bound state for longer, so this is an activating oncogenic alteration. The useful observation is biochemical direction, not merely the gene name.

Prediction exercise: the only functional RB1 copy is deleted

Cell-cycle restraint falls because RB1 activity is lost. This is suppressor logic, even though the DNA event is a deletion rather than a point mutation.

Promoter CpG hypermethylation can reduce transcription and silence a tumor suppressor without changing its coding sequence. Aging tissues show complex methylome changes, including broad hypomethylation, focal hypermethylation, and epigenetic drift. [4]

TP53 is altered in roughly half of human cancers, which makes it important but not a default answer whenever a cancer gene is uncertain. The case still has to fit TP53 biology, such as impaired DNA-damage response or a Li-Fraumeni pattern. Mutant p53 can show loss of function, dominant-negative effects, and context-dependent acquired activities. [3]

Try it here · Checkpoint 1 of 3

Make your prediction before reading the choices. A first attempt is just a starting point.

Case 1

A 67-year-old man with pancreatic ductal adenocarcinoma has a KRAS p.G12D variant in the tumor. In a biochemical assay, the mutant RAS protein remains predominantly GTP-bound after removal of the upstream growth-factor signal, whereas wild-type RAS becomes GDP-bound. Which molecular consequence best explains this result?

Show answer and explanations for case 1

  1. A. Impaired RAS GTP hydrolysis (Best answer)

    The assay directly shows failure to return efficiently to the GDP-bound state, which is the activating direction expected for an oncogenic RAS variant.

    Reasoning steps for option A
    1. What does the assay show about the mutant protein after the growth-factor signal is removed?

      Mutant RAS stays mostly GTP-bound, while wild-type RAS returns to the GDP-bound resting state.

    2. Why does a persistent GTP-bound state point to reduced GTP hydrolysis?

      RAS switches itself off by hydrolyzing GTP to GDP, so a G12D protein that stays GTP-bound keeps signaling without input, which is oncogene activation.

  2. B. Loss of β-catenin degradation after biallelic APC inactivation (Why this does not fit)

    APC loss can activate Wnt signaling, but it does not explain the measured persistence of GTP-bound RAS in this tumor.

    Reasoning steps for option B
    1. Why could Wnt pathway activation tempt someone in a pancreatic carcinoma?

      APC loss is a classic suppressor route to uncontrolled epithelial growth in the gastrointestinal tract.

    2. Which assay result does APC loss fail to explain?

      APC regulates β-catenin degradation, and it has no role in whether KRAS stays GTP-bound after the signal is withdrawn.

  3. C. Failure of homologous recombination after BRCA1 loss (Why this does not fit)

    BRCA1 deficiency impairs DNA double-strand break repair rather than the GTPase cycle measured in the assay.

    Reasoning steps for option C
    1. What makes a DNA-repair defect attractive in an aggressive adenocarcinoma?

      BRCA1-associated repair failure does occur in some pancreatic cancers and drives genomic instability.

    2. Why does repair failure not match the biochemical readout?

      The measured defect is in the GTPase cycle of a single protein, not in repair of double-strand breaks.

  4. D. Stabilization of HIF after loss of VHL protein (Why this does not fit)

    VHL loss changes oxygen-responsive protein degradation, not the GDP-GTP state of KRAS.

    Reasoning steps for option D
    1. Why might HIF stabilization seem relevant to a solid tumor with growth signaling?

      HIF activity drives angiogenic programs that many tumors exploit.

    2. What separates VHL loss from the KRAS result?

      VHL governs oxygen-dependent HIF degradation, whereas the assay tracks the GDP-GTP state of a mutant KRAS protein.

Takeaway: An activating RAS variant can prolong the GTP-bound signaling state, an oncogene gain-of-function pattern.

Case sources: [1]

RB1 shows how inherited risk and tumor formation are different events

Knudson inferred the two-hit model from the age and laterality of retinoblastoma. A child with a constitutional pathogenic RB1 variant already carries one altered copy in every cell. A susceptible retinal cell needs an additional somatic event affecting the remaining functional copy, so tumors tend to occur earlier and can be bilateral or multifocal. A sporadic tumor generally requires both relevant events to arise in the same retinal lineage. [2] [5]

Two timelines compare a constitutional first RB1 hit followed by a retinal second hit with two somatic RB1 hits arising in one retinal lineage.
Both routes converge on insufficient RB1 function in a retinal tumor cell, but heritable susceptibility starts one event earlier. [2] [5]

RB protein restrains the G1/S transition by limiting E2F-dependent transcription. When functional RB is absent, E2F-dependent S-phase programs are less restrained. The practical sequence is inherited first hit, tissue-specific second hit, then clonal expansion. The inheritance of susceptibility can therefore look dominant in a pedigree even though loss of RB1 function in an individual cell follows suppressor logic. [1] [5]

Heritable pattern

One pathogenic RB1 copy is constitutional. A later retinal event affects the remaining functional copy. Early onset, bilateral disease, or multiple tumors should increase concern for heritable retinoblastoma. [5]

Sporadic pattern

Blood testing can be negative while the retinal tumor contains two somatic RB1-disrupting events. A later unilateral presentation is more compatible with this route, although clinical evaluation still determines the individual diagnosis. [5]

A second hit is not restricted to a second small mutation. Loss of a chromosome segment, mitotic recombination, or another event that eliminates the remaining functional allele can create loss of heterozygosity. Read what happened to function, not only the mutation label. [1] [2]

Prediction exercise: bilateral retinal tumors at 18 months plus an affected parent

The family history and bilateral early presentation favor a constitutional RB1 first hit followed by independent somatic events in retinal cells. The tumor still requires loss of sufficient RB function.

Leukocoria is an important presentation of retinoblastoma, but a white pupillary reflex is not itself a gene test. Gene interpretation belongs beside the eye findings, family history, laterality, and molecular data. [5]

Try it here · Checkpoint 2 of 3

Make your prediction before reading the choices. A first attempt is just a starting point.

Case 4

An 18-month-old girl has bilateral multifocal retinoblastomas. Her father was treated for retinoblastoma as a child. Blood testing identifies a pathogenic RB1 variant, and one eye tumor has lost the remaining normal RB1 allele. Which sequence best explains tumor formation?

Show answer and explanations for case 4

  1. A. Two independent activating RB1 variants in the same retinal cell (Why this does not fit)

    RB1 is a tumor suppressor, so retinoblastoma is linked to loss of RB function rather than activating RB1 variants.

    Reasoning steps for option A
    1. Why might two RB1 variants in one cell seem to fit bilateral tumors?

      Two RB1 events are indeed needed within a retinal cell for the tumor to form.

    2. What is wrong with calling the RB1 changes activating?

      RB1 is a tumor suppressor, and the tumor lost the normal allele, so the pathway works through loss of RB function.

  2. B. A somatic BCR::ABL1 fusion followed by germline transmission (Why this does not fit)

    BCR::ABL1 is an acquired leukemia driver and does not explain this familial bilateral retinal tumor pattern.

    Reasoning steps for option B
    1. Why might a fusion gene be considered for an inherited cancer?

      BCR::ABL1 is the best-known example of a single genetic event that drives cancer.

    2. Which findings exclude a Philadelphia fusion here?

      BCR::ABL1 is an acquired leukemia driver, and this family shows inherited bilateral retinal tumors with an RB1 variant.

  3. C. A constitutional MYC rearrangement followed by ERBB2 amplification (Why this does not fit)

    Those oncogenic events do not match the inherited RB1 result or the tumor-specific loss of the normal RB1 allele.

    Reasoning steps for option C
    1. Why could oncogene events attract attention in an aggressive childhood tumor?

      MYC and ERBB2 changes are powerful drivers of rapidly growing cancers.

    2. Which test results point away from these oncogenes?

      Blood shows a pathogenic RB1 variant, and the tumor lost the remaining normal RB1 allele, which is suppressor loss.

  4. D. Constitutional RB1 hit plus a retinal somatic hit (Best answer)

    The inherited variant supplies the first hit throughout the body, and loss of the remaining functional allele in retinal cells completes the classic suppressor pattern.

    Reasoning steps for option D
    1. What do the father's history and the blood test show about the first event?

      The pathogenic RB1 variant is constitutional and inherited, so every retinal cell starts with one hit.

    2. How does the tumor finding complete the explanation for bilateral multifocal disease?

      A retinal cell that loses the remaining normal RB1 allele has no functional RB, and because every cell carries the first hit, several tumors can arise early in both eyes.

Takeaway: Heritable retinoblastoma supplies one RB1 hit constitutionally, so fewer additional events are needed in each susceptible retinal cell.

Case sources: [2] [5]

Oncogenes can be activated by mutation, amplification, or rearrangement

RAS proteins are small GTPases. Activating variants can impair the transition back toward the GDP-bound inactive state, extending proliferative signaling. BRAF is a downstream kinase in the same broad MAPK signaling axis, and an activating BRAF variant can drive signaling without requiring a lost second allele. [1]

ERBB2 illustrates amplification. A breast tumor can carry many additional copies of the HER2-encoding locus, increasing receptor abundance and signaling. Copy-number gain is therefore an oncogenic mechanism even when the receptor coding sequence is unchanged. [1]

BCR::ABL1 illustrates a fusion oncogene. The t(9;22) Philadelphia rearrangement creates a constitutively active tyrosine kinase central to chronic myeloid leukemia. Marked leukocytosis with a spectrum of myeloid maturation and basophilia should make the cytogenetic result mechanistically meaningful rather than decorative. [11]

MYC in Burkitt lymphoma shows a different rearrangement principle. The classic t(8;14) places MYC under strong immunoglobulin regulatory influence, increasing MYC expression in a B cell. The same broad category, chromosomal rearrangement, can therefore activate cancer through a new fusion protein or through abnormal control of an intact gene. [12]

Four panels show activating point variants, gene amplification, kinase fusion, and regulatory rearrangement with representative genes.
Different DNA events can converge on the same functional direction: increased positive signaling. [1] [11] [12] [14]

ALK rearrangements define a molecular subset of lung adenocarcinoma in which kinase signaling can become constitutive. The alteration matters because it identifies a driver pathway rather than merely a chromosome abnormality. [14]

RET is a receptor tyrosine kinase. Germline activating RET variants cause MEN2, with medullary thyroid carcinoma as a central feature and pheochromocytoma in MEN2A and MEN2B. MEN2A also includes risk of primary hyperparathyroidism. This is inherited oncogene activation, not a hereditary tumor suppressor syndrome. [13]

High-risk HPV demonstrates that cancer can also arise when viral proteins disable host safeguards. HPV E6 promotes p53 degradation, while E7 disrupts pRB control of E2F. The viral genes are oncogenic because their products reduce the function of host TP53 and RB1 pathways. [16]

Prediction exercise: a tumor has many ERBB2 copies but no coding variant

The copy-number change can itself increase receptor abundance. Classify the event as amplification-based oncogene activation rather than requiring an activating sequence variant.

Inherited tumor suppressor syndromes point to the pathway that lost protection

BRCA1 and BRCA2 support homologous recombination repair of DNA double-strand breaks. Germline pathogenic variants increase risks for breast and ovarian cancer; BRCA2 is also strongly associated with male breast, prostate, and pancreatic cancer. Tumors can become highly dependent on alternate DNA-repair processes once homologous recombination is deficient. [9]

A central cancer cell is linked to RB1 and TP53 cell-cycle control, BRCA repair, APC β-catenin control, VHL oxygen sensing, and NF1 RAS regulation.
Inherited syndromes become easier to distinguish when each gene is linked to the protective process that fails. [3] [6] [8] [9] [10]

APC helps control β-catenin in the Wnt pathway. In familial adenomatous polyposis, germline APC loss creates a field of susceptible colonic epithelium. Additional somatic loss in individual clones permits β-catenin accumulation and contributes to the development of numerous adenomas and very high colorectal cancer risk without preventive management. [10]

VHL protein participates in oxygen-sensitive degradation of HIF-α subunits under normoxic conditions. Loss of VHL permits HIF-dependent transcription, including angiogenic programs such as VEGF. The syndrome links clear cell renal cell carcinoma with retinal and central nervous system hemangioblastomas and pheochromocytoma or paraganglioma. [8]

NF1 encodes neurofibromin, a RAS GTPase-activating protein that helps restrain RAS signaling. Café-au-lait macules, axillary or inguinal freckling, neurofibromas, Lisch nodules, and optic pathway glioma fit NF1. The gene is at 17q11.2. [6]

NF2 encodes merlin at 22q12.2. Bilateral vestibular schwannomas are characteristic, and meningiomas and other schwannomas can occur. Current GeneReviews terminology is NF2-related schwannomatosis, replacing older wording such as central neurofibromatosis. [7]

WT1 belongs in a Wilms tumor predisposition framework, but WAGR and hemihyperplasia should not be fused into one mnemonic. WAGR is associated with a constitutional 11p13 deletion involving WT1 and PAX6 and can include Wilms tumor risk, aniridia, genitourinary abnormalities, and developmental disability. Isolated hemihyperplasia and Beckwith-Wiedemann spectrum are instead linked to the 11p15 region. [15]

Use phenotype to identify the missing safeguard
PatternSafeguardPathway consequence
Hundreds to thousands of colorectal adenomasAPCβ-catenin control is lost
Breast and ovarian family patternBRCA1/2Homologous recombination is impaired
Clear cell RCC plus hemangioblastomasVHLHIF signaling persists in normoxia
Café-au-lait macules plus neurofibromasNF1RAS restraint is reduced
Bilateral vestibular schwannomasNF2Merlin-dependent growth restraint is lost
Prediction exercise: normal oxygen but high HIF and VEGF in a clear cell renal tumor

Loss of VHL function can prevent normal HIF degradation, so a normoxic cell behaves as though a hypoxic transcriptional program should remain active.

Try it here · Checkpoint 3 of 3

Make your prediction before reading the choices. A first attempt is just a starting point.

Case 15

A 28-year-old woman has a clear cell renal cell carcinoma, retinal angiomas, and a cerebellar hemangioblastoma. Tumor cells show high HIF target-gene expression and high VEGF despite normal oxygen tension. Which molecular defect best explains the laboratory pattern?

Show answer and explanations for case 15

  1. A. Activating RB1 mutation that increases E2F restraint (Why this does not fit)

    RB1 is a suppressor and the proposed direction is internally inconsistent; it also does not fit the VHL syndrome phenotype.

    Reasoning steps for option A
    1. Why might an RB1 change be considered in a young adult with several tumors?

      RB1 is a well-known inherited tumor suppressor.

    2. What is internally inconsistent about an activating RB1 change here?

      Tumor suppressors cause cancer by losing function, and RB1 does not explain renal cancer, retinal angiomas and hemangioblastoma.

  2. B. Loss of MYC expression after t(8;14) (Why this does not fit)

    t(8;14) increases MYC expression in Burkitt lymphoma rather than producing this renal and hemangioblastoma pattern.

    Reasoning steps for option B
    1. Why might MYC be linked to a tumor with high target-gene expression?

      MYC is a strong transcriptional driver of growth programs.

    2. What is wrong with MYC loss after t(8;14)?

      t(8;14) increases MYC in Burkitt lymphoma, and MYC does not regulate normoxic HIF and VEGF.

  3. C. Increased neurofibromin activity that suppresses RAS (Why this does not fit)

    NF1 biology does not account for normoxic HIF stabilization and the VHL-associated tumor spectrum.

    Reasoning steps for option C
    1. Why could a RAS regulator be considered in an inherited tumor syndrome?

      NF1 is another suppressor syndrome with tumors of the nervous system.

    2. Which findings point away from neurofibromin?

      Increased neurofibromin would lower RAS signaling and cannot stabilize HIF in normal oxygen, and the tumor spectrum is that of VHL.

  4. D. Loss of VHL-dependent HIF degradation (Best answer)

    The syndrome and normoxic HIF-VEGF activation fit loss of pVHL-mediated degradation of HIF-α subunits.

    Reasoning steps for option D
    1. What do clear cell renal cancer, retinal angiomas and a cerebellar hemangioblastoma suggest together?

      They form the von Hippel-Lindau tumor spectrum.

    2. Why are HIF targets and VEGF high despite normal oxygen?

      pVHL normally tags HIF-α for degradation when oxygen is present, so its loss lets HIF-α accumulate and drive VEGF as if the cell were hypoxic.

Takeaway: VHL loss permits HIF-dependent transcription to persist in normoxia, promoting angiogenic programs.

Case sources: [8]

Tumor names and metastatic sites need context, not shortcuts

The suffix -oma does not guarantee benign behavior. Lymphoma, melanoma, mesothelioma, and seminoma are malignant. Hepatoma is an older term commonly used for hepatocellular carcinoma. Teratoma behavior depends strongly on site, age, and histology, so it should not be treated as a universal benign-or-malignant suffix exception. [18]

Metastatic cancer can spread to almost any organ, and the preferred destinations depend on the primary tumor. Bone, liver, and lung are frequent metastatic sites across common cancers, with brain and adrenal involvement important for selected primaries. It is safer to identify the known primary, lesion distribution, and pathology than to memorize a universal six-site rule or assume every lesion at one organ is more likely metastatic than primary. [17]

For example, multiple liver lesions in a patient with colorectal adenocarcinoma can represent metastatic colorectal carcinoma, especially when morphology and immunophenotype match the colon primary. A solitary liver mass in a cirrhotic patient raises a different differential. The organ name alone does not determine whether a tumor is primary or metastatic. [17]

The practical synthesis is consistent across the lesson: identify whether the genetic event adds signaling or subtracts protection, then connect the event to the phenotype. A gene name is useful only when its functional direction explains the clinical and molecular findings.

Prediction exercise: prior colon cancer plus multiple CDX2-positive liver lesions

The known primary, multifocal distribution, matching morphology, and intestinal immunophenotype support metastatic colorectal carcinoma rather than a liver-origin diagnosis based only on location.

Apply the direction and pathway logic

Case 2

A 54-year-old woman has an invasive breast carcinoma. Tumor sequencing shows 14 copies of ERBB2, markedly increased ERBB2 messenger RNA, and strong HER2 membrane expression, but no activating ERBB2 coding variant. Which genetic mechanism is driving the abnormal signal?

Show answer and explanations for case 2

  1. A. Loss of heterozygosity at a tumor suppressor locus (Why this does not fit)

    Loss of heterozygosity decreases functional suppressor dosage; this tumor instead has a large increase in ERBB2 copy number.

    Reasoning steps for option A
    1. Why might loss of heterozygosity come to mind for a breast carcinoma?

      Loss of heterozygosity is common in breast tumors, especially at suppressor loci such as BRCA1 and BRCA2.

    2. Which sequencing result points in the opposite direction?

      The tumor gained ERBB2 copies to 14 per cell, and loss of heterozygosity removes an allele rather than adding copies.

  2. B. Promoter hypermethylation that silences transcription (Why this does not fit)

    Promoter silencing would decrease transcript abundance, opposite the markedly increased ERBB2 messenger RNA reported here.

    Reasoning steps for option B
    1. What could make an epigenetic mechanism seem plausible when no coding variant is found?

      Epigenetic changes can alter gene activity without any change in the coding sequence.

    2. Why does the ERBB2 transcript level rule out promoter silencing?

      Silencing lowers messenger RNA, but ERBB2 messenger RNA is markedly increased here.

  3. C. Gene amplification that increases receptor dosage (Best answer)

    The concordant high copy number, transcript abundance, and protein expression support oncogenic amplification rather than coding-sequence activation.

    Reasoning steps for option C
    1. What do the copy number, transcript and protein results have in common?

      All three are increased together: 14 ERBB2 copies, abundant ERBB2 messenger RNA and strong HER2 membrane staining.

    2. How can a normal coding sequence still drive oncogenic signaling?

      Extra gene copies raise receptor dosage, and the excess HER2 increases signaling without any activating variant, so amplification is the driver.

  4. D. A germline first hit followed by retinal somatic loss (Why this does not fit)

    That sequence describes heritable RB1 predisposition and does not explain ERBB2 copy-number gain in a breast tumor.

    Reasoning steps for option D
    1. Why might a two-hit sequence be considered for a woman with breast cancer?

      Inherited first-hit syndromes such as BRCA-related cancer predispose to breast tumors.

    2. What in the tumor data does a retinal two-hit sequence fail to address?

      It describes heritable RB1 loss in the retina and cannot produce a gain of ERBB2 copies in breast tissue.

Takeaway: Oncogenes can be activated by copy-number amplification even when the coding sequence is unchanged.

Case sources: [1]

Case 3

A 32-year-old woman with an osteosarcoma has a mother who developed breast cancer at age 29 and a brother who had adrenocortical carcinoma in childhood. Germline testing finds a pathogenic TP53 variant. Cultured tumor cells fail to induce p21 after ionizing radiation. Which lost cellular response most directly fits these findings?

Show answer and explanations for case 3

  1. A. Oxygen-dependent HIF degradation (Why this does not fit)

    That response depends on VHL and would not explain the Li-Fraumeni pedigree or absent p21 induction after radiation.

    Reasoning steps for option A
    1. Why might an oxygen-sensing defect be considered in a family with many early cancers?

      VHL loss is an inherited suppressor defect that also causes cancer in young adults.

    2. Which findings argue against the VHL pathway?

      The pedigree of early breast cancer, childhood adrenocortical carcinoma and sarcoma, plus absent p21 after radiation, fits TP53 rather than HIF regulation.

  2. B. p53-dependent p21 induction with DNA-damage cell-cycle arrest (Best answer)

    The pedigree fits Li-Fraumeni syndrome and the failed p21 response indicates impaired p53-mediated arrest after DNA damage.

    Reasoning steps for option B
    1. What does the family tumor spectrum suggest before the genetic result is read?

      Osteosarcoma, breast cancer at 29 and childhood adrenocortical carcinoma form the classic Li-Fraumeni pattern.

    2. How does the failed p21 response connect to the TP53 variant?

      After ionizing radiation, p53 normally induces p21 to halt the cell cycle, so absent p21 shows the lost p53 damage response.

  3. C. RAS conversion from GTP-bound to GDP-bound state (Why this does not fit)

    Neurofibromin and RAS GTPase activity regulate this process, not TP53-dependent p21 induction.

    Reasoning steps for option C
    1. Why could a RAS-control defect seem relevant in a hereditary sarcoma family?

      NF1 loss raises RAS signaling and can predispose to sarcomas, including malignant nerve sheath tumors.

    2. What result places the defect outside RAS regulation?

      The cells fail specifically to induce p21 after DNA damage, which is a p53 transcriptional response, not a RAS GTPase function.

  4. D. β-catenin destruction in resting colonic epithelium (Why this does not fit)

    APC regulates β-catenin; the supplied family tumor spectrum and radiation-response defect point to TP53.

    Reasoning steps for option D
    1. Why might β-catenin control be considered in a family with inherited tumors?

      APC loss is a well-known inherited suppressor defect that causes early cancer.

    2. Which features separate the family from an APC pattern?

      There is no colonic polyposis, and the radiation-response defect with a pathogenic TP53 variant points to p53.

Takeaway: TP53 loss impairs DNA-damage responses such as p21-mediated cell-cycle arrest, and the clinical setting must fit the gene.

Case sources: [3]

Case 5

A 5-year-old boy has a single unilateral retinoblastoma and no family history of the disease. Blood testing does not identify a pathogenic RB1 variant. Tumor sequencing finds two independent inactivating RB1 events. Which interpretation is most consistent with this pattern?

Show answer and explanations for case 5

  1. A. One RB1 hit must have been inherited but was missed because the tumor is unilateral (Why this does not fit)

    An inherited variant is possible in some unilateral cases, but the supplied testing instead demonstrates two tumor-restricted events and no blood variant.

    Reasoning steps for option A
    1. Why is an inherited RB1 variant a reasonable concern in any child with retinoblastoma?

      Some children with unilateral disease still carry a constitutional RB1 variant.

    2. Which results make an inherited first hit unlikely here?

      Blood testing is negative, there is no family history, and both RB1 events are confined to the tumor.

  2. B. Two somatic RB1 hits in one retinal lineage (Best answer)

    A unilateral later presentation with negative blood testing and two tumor-restricted RB1 events fits a sporadic two-somatic-hit route.

    Reasoning steps for option B
    1. What do the negative blood test and single tumor suggest about the route?

      A unilateral tumor in an older child without a family history fits the sporadic pattern.

    2. How do the two tumor-restricted events fit the two-hit model?

      Both RB1 copies were inactivated somatically in the same retinal lineage, so RB function was lost without an inherited first hit.

  3. C. One activating RB1 allele was sufficient to create the tumor (Why this does not fit)

    RB1 is a suppressor, so gain of RB1 activity does not fit the loss-of-function events reported.

    Reasoning steps for option C
    1. Why might a single gene event seem enough to start this tumor?

      One activated allele is enough for an oncogene, and the boy has only one tumor.

    2. Why does single-allele sufficiency not apply to RB1?

      RB1 is a suppressor, and sequencing found two inactivating events, not a gain of RB activity.

  4. D. The tumor is best explained by inherited RET activation (Why this does not fit)

    RET activation is linked to MEN2, not the two inactivating RB1 events documented in this retinal tumor.

    Reasoning steps for option D
    1. Why might an inherited activating variant come to mind for a childhood tumor?

      Germline RET activation is a classic cause of inherited cancer in young people.

    2. What in the tumor points away from RET?

      RET activation causes MEN2 thyroid and adrenal tumors, while this retinal tumor carries two inactivating RB1 events.

Takeaway: Sporadic retinoblastoma can acquire both relevant RB1-disrupting events within the tumor lineage.

Case sources: [2] [5]

Case 6

A 58-year-old man has fatigue, early satiety, splenomegaly, a leukocyte count of 118,000/µL, basophilia, and circulating myeloid cells at multiple maturation stages. Cytogenetic testing identifies t(9;22). Which abnormal protein activity is most directly responsible for this disease?

Show answer and explanations for case 6

  1. A. Constitutive BCR::ABL1 tyrosine kinase signaling (Best answer)

    The clinical blood pattern and Philadelphia rearrangement identify CML driven by the BCR::ABL1 fusion kinase.

    Reasoning steps for option A
    1. What do the blood count and spleen findings suggest before cytogenetics?

      Marked leukocytosis with basophilia, myeloid cells at all maturation stages and splenomegaly fit chronic myeloid leukemia.

    2. What does t(9;22) produce that drives the disease?

      The Philadelphia rearrangement fuses BCR to ABL1, creating a tyrosine kinase that signals constantly and drives myeloid proliferation.

  2. B. Constitutive MYC expression from an immunoglobulin enhancer (Why this does not fit)

    MYC-immunoglobulin rearrangement is characteristic of Burkitt lymphoma and uses a different translocation.

    Reasoning steps for option B
    1. Why might MYC overexpression seem to fit a very high white count?

      MYC translocations drive rapid proliferation in hematologic cancers.

    2. Which finding separates MYC-driven disease from this case?

      MYC-immunoglobulin rearrangements are typical of Burkitt lymphoma from t(8;14), not a myeloid leukemia with t(9;22).

  3. C. Loss of VHL-mediated HIF degradation (Why this does not fit)

    VHL loss is associated with clear cell renal cancer and hemangioblastomas, not t(9;22) myeloid leukemia.

    Reasoning steps for option C
    1. Why could a suppressor defect be considered in a patient with a large spleen?

      VHL loss increases VEGF and erythropoietin signaling, which can affect blood counts.

    2. What makes VHL loss a poor fit for this blood picture?

      VHL loss causes clear cell renal cancer and hemangioblastomas, and it does not produce the Philadelphia chromosome.

  4. D. Loss of APC-dependent β-catenin control (Why this does not fit)

    APC loss drives colorectal neoplasia and does not produce the Philadelphia chromosome.

    Reasoning steps for option D
    1. Why might Wnt activation be considered for uncontrolled proliferation?

      Loss of β-catenin control is a common growth driver in epithelial cancers.

    2. Which result shows the disease is driven by a different event?

      The cytogenetic finding is t(9;22), a myeloid fusion, whereas APC loss drives colorectal neoplasia.

Takeaway: t(9;22) creates BCR::ABL1, an oncogenic fusion with constitutive tyrosine kinase activity.

Case sources: [11]

Case 7

A 9-year-old boy from equatorial Africa develops a rapidly growing jaw mass. Biopsy shows a high-grade B-cell lymphoma with a starry-sky appearance, and cytogenetics identifies t(8;14). Which consequence of the rearrangement best explains the tumor biology?

Show answer and explanations for case 7

  1. A. Creation of a constitutively active BCR::ABL1 fusion kinase (Why this does not fit)

    BCR::ABL1 comes from t(9;22), not the t(8;14) rearrangement in this B-cell lymphoma.

    Reasoning steps for option A
    1. Why might a fusion kinase seem attractive for a translocation-driven cancer?

      BCR::ABL1 is the classic example of a translocation that creates an active oncogenic protein.

    2. Which translocation in this child argues against BCR::ABL1?

      BCR::ABL1 comes from t(9;22), but this lymphoma carries t(8;14).

  2. B. Loss of both RB1 alleles at chromosome 13q14 (Why this does not fit)

    RB1 loss can drive retinoblastoma and other tumors, but it does not explain the specified MYC translocation.

    Reasoning steps for option B
    1. Why could RB1 loss be considered in a child with a fast-growing tumor?

      Loss of RB1 removes G1/S restraint and drives several childhood tumors.

    2. What does RB1 loss fail to explain in this biopsy?

      The defining lesion is a translocation of MYC on chromosome 8, not loss of both RB1 alleles on 13q14.

  3. C. MYC overexpression under immunoglobulin control (Best answer)

    The t(8;14) rearrangement places MYC near immunoglobulin regulatory elements and drives intense proliferative transcription.

    Reasoning steps for option C
    1. What do the jaw mass, geography and starry-sky pattern suggest?

      A rapidly growing jaw mass in an African child with a starry-sky B-cell lymphoma is endemic Burkitt lymphoma.

    2. How does t(8;14) activate an intact gene without making a fusion protein?

      It moves MYC next to immunoglobulin heavy-chain regulatory elements, so the normal MYC protein is expressed at high levels in B cells.

  4. D. Amplification of ERBB2 with excess HER2 receptor (Why this does not fit)

    ERBB2 amplification is a copy-number mechanism seen in a subset of breast and other cancers, not this t(8;14) lymphoma.

    Reasoning steps for option D
    1. Why might excess growth-factor receptor seem to explain a rapidly proliferating tumor?

      ERBB2 amplification is a well-known copy-number driver of aggressive cancer.

    2. What separates amplification from the genetic finding here?

      The lymphoma has a balanced t(8;14) rearrangement, not extra ERBB2 copies, and ERBB2 amplification is a breast and gastric pattern.

Takeaway: A regulatory translocation can activate an oncogene by increasing expression rather than by making a fusion protein.

Case sources: [12]

Case 8

A melanoma contains a heterozygous BRAF p.V600E variant. The second BRAF allele is intact, yet phospho-ERK remains high without the usual upstream stimulation. Which principle best accounts for tumor signaling from only one altered allele?

Show answer and explanations for case 8

  1. A. Both alleles of every cancer gene must be lost before signaling changes (Why this does not fit)

    That oversimplifies the classic tumor suppressor model and conflicts with the activating BRAF result.

    Reasoning steps for option A
    1. Why is a two-allele requirement tempting when one BRAF allele is still normal?

      The two-hit rule is the most familiar model of how cancer genes lose control.

    2. What does the high phospho-ERK show about that requirement?

      Signaling is already abnormal with one intact allele, so the altered gene acts as an oncogene and does not need both copies changed.

  2. B. One activated BRAF allele supplies the abnormal signal (Best answer)

    Persistent downstream MAPK activity despite one intact allele is the expected cellular-dominant behavior of an activated oncogene.

    Reasoning steps for option B
    1. What does the persistent phospho-ERK show about the MAPK pathway?

      ERK stays phosphorylated without upstream stimulation, so the pathway is active on its own.

    2. Why is one V600E allele enough to produce that signal?

      The mutant kinase is constitutively active, so its product supplies the abnormal signal even while the normal allele keeps making normal BRAF.

  3. C. The intact allele is necessarily methylated even though no methylation data are given (Why this does not fit)

    No evidence of epigenetic silencing is supplied, and an activating oncogene does not require loss of the normal allele.

    Reasoning steps for option C
    1. Why might silencing of the normal allele be proposed?

      Epigenetic silencing is a real way to remove the remaining allele of a cancer gene.

    2. What evidence is missing for silencing, and why is it unnecessary?

      No methylation data are given, and an activated oncogene drives signaling even with a working normal allele.

  4. D. BRAF is acting as a DNA-repair tumor suppressor in this tumor (Why this does not fit)

    BRAF is a signaling kinase; the observed high phospho-ERK supports pathway activation rather than loss of DNA repair.

    Reasoning steps for option D
    1. Why could a suppressor label be considered for a common melanoma gene?

      Melanomas carry many DNA-damage changes from ultraviolet light.

    2. Which result shows BRAF is acting in the opposite direction?

      Phospho-ERK is high without upstream stimulation, which is a gain of kinase signaling; a lost repair gene would raise mutation burden, not switch on the MAPK pathway.

Takeaway: Activated oncogenes can show cellular-dominant behavior because one altered allele can provide an abnormal positive signal.

Case sources: [1]

Case 9

A 41-year-old never-smoker with lung adenocarcinoma has an EML4::ALK fusion. The tumor shows ALK kinase activity despite absence of the normal extracellular stimulus. Which functional description best fits this alteration?

Show answer and explanations for case 9

  1. A. A second somatic hit abolishes a DNA-repair suppressor (Why this does not fit)

    The reported lesion is a fusion driver with kinase activity, not biallelic loss of a repair gene.

    Reasoning steps for option A
    1. Why could a lost repair suppressor be considered in lung adenocarcinoma?

      Lung cancers often carry repair and checkpoint defects that allow genomic instability.

    2. What does the molecular report actually show?

      The tumor has an active ALK fusion kinase, a gain of signaling, not biallelic loss of a repair gene.

  2. B. Promoter methylation suppresses ALK transcript production (Why this does not fit)

    The tumor has active ALK signaling; silencing ALK transcription would predict the opposite direction.

    Reasoning steps for option B
    1. Why might a transcriptional mechanism be proposed for a gene rearrangement?

      Rearrangements can change how strongly a gene is transcribed.

    2. Why does silencing contradict the ALK finding?

      The tumor shows ALK kinase activity, and silencing ALK transcription would reduce, not create, that activity.

  3. C. Loss of HIF degradation creates the ALK fusion (Why this does not fit)

    VHL-HIF regulation is a separate oxygen-sensing pathway and does not generate EML4::ALK.

    Reasoning steps for option C
    1. Why might HIF signaling be linked to a lung tumor that grows without its normal stimulus?

      HIF stabilization lets tumor cells act as if hypoxic and drives angiogenic growth.

    2. What separates oxygen sensing from how an EML4::ALK fusion forms?

      VHL-HIF regulation does not rearrange chromosomes, and the fusion arises from a structural rearrangement of chromosome 2.

  4. D. The ALK fusion creates constitutive oncogenic kinase signaling (Best answer)

    EML4::ALK is an oncogenic fusion that can drive ligand-independent kinase activity in a molecular subset of lung adenocarcinoma.

    Reasoning steps for option D
    1. What does kinase activity without the normal stimulus indicate?

      ALK is signaling constitutively, which is the gain-of-function direction of an oncogene.

    2. How does the EML4::ALK fusion produce that activity?

      The EML4 partner promotes clustering of the ALK kinase domain, which activates it without ligand and defines a treatable subset of never-smoker adenocarcinoma.

Takeaway: Gene fusions can create constitutively active oncogenic kinases.

Case sources: [14]

Case 10

A 29-year-old woman has medullary thyroid carcinoma and a prior pheochromocytoma. Her father and paternal aunt had similar tumors. Germline testing identifies a pathogenic RET variant that increases receptor signaling. Which genetic category best describes the inherited lesion?

Show answer and explanations for case 10

  1. A. Biallelic tumor suppressor deletion (Why this does not fit)

    The reported variant increases RET signaling rather than abolishing a suppressive function.

    Reasoning steps for option A
    1. Why might a suppressor deletion be considered in a family with several endocrine tumors?

      Many inherited cancer syndromes arise from suppressor loss passed through families.

    2. What does the genetic report say about the direction of change?

      The RET variant increases receptor signaling, so it adds function rather than deleting a suppressor.

  2. B. Homologous recombination repair defect (Why this does not fit)

    That category fits BRCA1/2 loss, not an activating RET receptor variant.

    Reasoning steps for option B
    1. Why could a repair defect be considered in a family with early cancers?

      BRCA1 and BRCA2 repair defects cause strong autosomal dominant family patterns.

    2. Which tumor combination points away from a repair defect?

      Medullary thyroid carcinoma with pheochromocytoma is the MEN2 pattern of RET activation, not a BRCA tumor spectrum.

  3. C. Activating oncogene variant (Best answer)

    MEN2 results from germline activating RET variants, so the inherited lesion adds receptor tyrosine kinase signaling.

    Reasoning steps for option C
    1. What do medullary thyroid carcinoma and pheochromocytoma in three relatives suggest?

      They form the multiple endocrine neoplasia type 2 pattern, inherited as an autosomal dominant trait.

    2. How does the RET result define the genetic category?

      A germline variant that increases RET receptor tyrosine kinase signaling is inherited oncogene activation, even though the syndrome runs in families like a suppressor disorder.

  4. D. Constitutional RB1 first hit (Why this does not fit)

    RB1 predisposition causes retinoblastoma and does not explain medullary thyroid carcinoma with pheochromocytoma.

    Reasoning steps for option D
    1. Why might an inherited first hit seem attractive in a familial tumor syndrome?

      Constitutional RB1 variants are the model of inherited cancer susceptibility.

    2. Which tumor types rule out RB1 predisposition here?

      Carriers of an RB1 first hit develop retinoblastoma in early childhood and later osteosarcoma, whereas this family has medullary thyroid carcinoma and pheochromocytoma with a RET gain.

Takeaway: Hereditary cancer can result from germline oncogene activation, as in RET-associated MEN2.

Case sources: [13]

Case 11

A cervical biopsy shows high-grade squamous intraepithelial lesion (HSIL/CIN 3) with integrated high-risk HPV. Laboratory studies show low p53 protein, increased free E2F activity, and continued cell-cycle entry despite DNA damage. Which paired viral effects best explain the findings?

Show answer and explanations for case 11

  1. A. E6 degrades p53; E7 releases E2F from pRB control (Best answer)

    The low p53 and increased E2F activity are the paired effects expected from high-risk HPV E6 and E7.

    Reasoning steps for option A
    1. What do low p53 and increased free E2F show in this cervical lesion?

      Two separate restraints are lost: the p53 damage response and pRB control of E2F.

    2. How do the two high-risk HPV proteins explain both losses?

      E6 promotes p53 degradation and E7 binds pRB to release E2F, so an HSIL (CIN 3) with integrated high-risk HPV keeps cycling despite DNA damage.

  2. B. E6 activates VHL and E7 degrades HIF (Why this does not fit)

    VHL-HIF biology does not explain the paired p53 loss and E2F release in high-risk HPV infection.

    Reasoning steps for option B
    1. Why could HIF biology be considered in a rapidly dividing epithelial lesion?

      Hypoxic signaling is common in neoplastic tissue and supports growth.

    2. Which laboratory changes are left unexplained by VHL and HIF?

      Neither accounts for the low p53 protein and the release of E2F from pRB control.

  3. C. E6 deletes APC and E7 amplifies ERBB2 (Why this does not fit)

    Neither APC loss nor ERBB2 amplification is the specific viral mechanism demonstrated by the supplied protein changes.

    Reasoning steps for option C
    1. Why might APC or ERBB2 changes seem plausible in a squamous neoplasm?

      Both are well-known drivers of epithelial cancer.

    2. What do the protein studies show instead?

      The measured changes are p53 loss and E2F release, which are the direct effects of E6 and E7, not Wnt or HER2 signaling.

  4. D. E6 activates BRCA1 and E7 activates BRCA2 (Why this does not fit)

    The observed defect is loss of p53 and pRB restraint, not increased homologous recombination activity.

    Reasoning steps for option D
    1. Why could altered BRCA activity seem relevant to DNA damage in this lesion?

      BRCA1 and BRCA2 handle DNA double-strand breaks, and the cells keep dividing despite damage.

    2. Why does increased BRCA activity point the wrong way?

      The lesion shows lost restraint, low p53 and free E2F, whereas more BRCA function would improve repair rather than remove checkpoints.

Takeaway: High-risk HPV E6 and E7 promote carcinogenesis by disabling p53 and pRB pathway control.

Case sources: [16]

Case 12

A 19-year-old man has hundreds of colorectal adenomas. Germline testing shows a pathogenic APC variant. An adenoma has lost the remaining functional APC allele and contains abundant nuclear β-catenin. Which downstream change best follows from the second APC hit?

Show answer and explanations for case 12

  1. A. Increased HIF degradation under normoxic conditions (Why this does not fit)

    VHL, not APC, governs HIF degradation, and suppressor loss would not predict increased HIF degradation.

    Reasoning steps for option A
    1. Why might HIF regulation come up in a suppressor syndrome?

      VHL is another inherited suppressor that controls protein degradation.

    2. Why does increased HIF degradation not follow from APC loss?

      APC does not regulate HIF, and loss of a suppressor would reduce degradation of its target, not increase it.

  2. B. Reduced GTP-bound RAS because neurofibromin is absent (Why this does not fit)

    NF1 loss tends to increase active RAS rather than reduce it, and this patient has APC-associated polyposis.

    Reasoning steps for option B
    1. Why might a RAS pathway change be considered in colorectal adenomas?

      KRAS activation is common as adenomas progress.

    2. What is wrong with lower RAS-GTP in this patient?

      Loss of neurofibromin raises active RAS rather than lowering it, and this patient has APC-associated polyposis, not NF1.

  3. C. Loss of BCR::ABL1 kinase activity after t(9;22) (Why this does not fit)

    The Philadelphia fusion is unrelated to APC loss and colorectal adenoma formation.

    Reasoning steps for option C
    1. Why could a kinase change be considered for uncontrolled epithelial growth?

      Constitutive kinase activity is a common oncogenic driver.

    2. What separates the Philadelphia fusion from this adenoma?

      t(9;22) is a myeloid leukemia event and has no link to APC loss in colonic epithelium.

  4. D. APC loss stabilizes β-catenin (Best answer)

    Loss of remaining APC function impairs β-catenin regulation, allowing nuclear accumulation and transcriptional activation.

    Reasoning steps for option D
    1. What do hundreds of adenomas and the germline APC variant indicate?

      Familial adenomatous polyposis, with one APC hit present in every colonic cell.

    2. What does the second APC hit do to β-catenin in the adenoma?

      Without functional APC, the destruction complex cannot degrade β-catenin, so it accumulates in the nucleus and activates Wnt target genes.

Takeaway: APC loss stabilizes β-catenin and increases Wnt-responsive transcription in colorectal neoplasia.

Case sources: [10]

Case 13

A 38-year-old woman with triple-negative breast cancer has a mother with ovarian cancer and a germline pathogenic BRCA1 variant. Tumor testing shows defective repair of DNA double-strand breaks using an intact homologous template. Which pathway is impaired?

Show answer and explanations for case 13

  1. A. Mismatch repair of single-base replication errors (Why this does not fit)

    Mismatch repair deficiency causes a different repair phenotype and does not explain the supplied BRCA1 variant.

    Reasoning steps for option A
    1. Why could mismatch repair be considered in a woman with a DNA repair defect?

      Mismatch repair deficiency is another inherited repair disorder that causes early cancers.

    2. Which tumor result points away from mismatch repair?

      The defect is in repair of double-strand breaks using a homologous template, and the germline variant is in BRCA1.

  2. B. Homologous recombination (Best answer)

    BRCA1 is central to homologous recombination, matching both the inherited cancer pattern and the tumor repair phenotype.

    Reasoning steps for option B
    1. What do triple-negative breast cancer and a mother with ovarian cancer suggest?

      They fit hereditary breast and ovarian cancer from a BRCA1 variant.

    2. Which repair pathway uses an intact homologous template for double-strand breaks?

      Homologous recombination, which requires BRCA1, so the tumor phenotype matches the inherited defect.

  3. C. VHL-dependent oxygen sensing (Why this does not fit)

    VHL-HIF regulation is unrelated to homologous-template repair of DNA double-strand breaks.

    Reasoning steps for option C
    1. Why could oxygen sensing be proposed in an aggressive breast cancer?

      HIF signaling supports angiogenesis and growth in many solid tumors.

    2. What tumor result excludes the VHL pathway as the impaired process?

      The measured defect is in template-directed repair of double-strand breaks, which VHL does not perform.

  4. D. RAS GTP hydrolysis (Why this does not fit)

    RAS signaling controls a growth pathway rather than homologous-template DNA repair.

    Reasoning steps for option D
    1. Why might RAS be considered in a tumor that grows despite damaged DNA?

      RAS activation drives proliferation in many carcinomas.

    2. Why does RAS not match the defect measured here?

      RAS controls growth signaling, while the tumor defect is in homologous-template DNA repair.

Takeaway: BRCA1 loss impairs homologous recombination repair of DNA double-strand breaks.

Case sources: [9]

Case 14

A 56-year-old man develops breast cancer. His father had metastatic prostate cancer and his paternal uncle had pancreatic cancer. Germline testing identifies a pathogenic BRCA2 variant, and the tumor has lost the normal BRCA2 copy. Which interpretation best integrates the pedigree and tumor result?

Show answer and explanations for case 14

  1. A. Inherited activation of a receptor tyrosine kinase followed by amplification (Why this does not fit)

    That mechanism fits oncogene syndromes such as RET activation, not a pathogenic BRCA2 variant with loss of the normal copy.

    Reasoning steps for option A
    1. Why might an inherited oncogene be considered in a family with several cancers?

      Germline activating variants such as RET cause dominant family cancer patterns.

    2. What in the genetic report shows loss rather than gain?

      The BRCA2 variant is pathogenic and the tumor lost the normal copy, which is suppressor loss, not receptor activation.

  2. B. Sporadic RB1 loss confined to retinal tissue (Why this does not fit)

    The family cancer spectrum and BRCA2 testing are incompatible with a retinal RB1-only process.

    Reasoning steps for option B
    1. Why might a two-hit suppressor model be applied to any tumor with a lost normal allele?

      RB1 is the textbook example of losing the second allele in a tumor.

    2. Which findings make an RB1-only process impossible here?

      The man has breast cancer with a BRCA2 variant and a family spectrum of prostate and pancreatic cancer, not retinal disease.

  3. C. BRCA2 first hit plus tumor loss of the normal copy (Best answer)

    The male breast, prostate, and pancreatic family pattern fits BRCA2, and tumor loss of the normal allele supplies further loss of repair capacity.

    Reasoning steps for option C
    1. What does the family combination of male breast, prostate and pancreatic cancer suggest?

      It is the characteristic cancer spectrum of a BRCA2 germline variant.

    2. How does the tumor result complete the explanation?

      The germline variant is the first hit, and loss of the normal BRCA2 copy in the tumor removes remaining homologous recombination capacity.

  4. D. A B-cell MYC rearrangement followed by immunoglobulin overexpression (Why this does not fit)

    MYC rearrangement drives aggressive B-cell lymphoma and does not explain this hereditary solid-tumor spectrum.

    Reasoning steps for option D
    1. Why could a MYC rearrangement be considered in an aggressive cancer?

      MYC activation drives rapid proliferation in several tumors.

    2. Why does a MYC event not fit this family?

      MYC rearrangement is a B-cell lymphoma mechanism, and this family has an inherited solid-tumor pattern with a BRCA2 variant.

Takeaway: BRCA2-associated cancer susceptibility reflects inherited loss of one repair copy with additional tumor-specific loss often contributing.

Case sources: [9]

Case 16

A 15-year-old girl has multiple café-au-lait macules, axillary freckling, cutaneous neurofibromas, and an optic pathway glioma. A tumor sample shows increased RAS-GTP. Which lost protein activity most directly explains the signaling result?

Show answer and explanations for case 16

  1. A. Loss of neurofibromin RAS-GAP activity (Best answer)

    NF1 encodes neurofibromin, which helps turn RAS signaling down by promoting GTP hydrolysis; its loss fits increased RAS-GTP.

    Reasoning steps for option A
    1. What do café-au-lait macules, axillary freckling, neurofibromas and optic glioma indicate?

      They are classic features of neurofibromatosis type 1.

    2. How does loss of neurofibromin raise RAS-GTP?

      Neurofibromin is a GTPase-activating protein that speeds RAS GTP hydrolysis, so without it RAS stays in the active GTP-bound state.

  2. B. Merlin-mediated regulation associated with NF2 (Why this does not fit)

    Merlin loss is linked to NF2-related schwannomatosis and bilateral vestibular schwannomas, not this NF1 phenotype or RAS-GTP finding.

    Reasoning steps for option B
    1. Why could merlin be considered in a teenager with nerve sheath tumors?

      NF2 is another neurofibromatosis gene that causes tumors of nerve sheath cells.

    2. Which findings separate NF1 from NF2 here?

      Café-au-lait macules, freckling, cutaneous neurofibromas and optic glioma fit NF1, while NF2 causes bilateral vestibular schwannomas.

  3. C. pVHL-mediated degradation of HIF (Why this does not fit)

    VHL loss produces a different tumor syndrome and oxygen-sensing defect rather than the classic NF1 findings.

    Reasoning steps for option C
    1. Why might VHL be considered for inherited tumors in a young person?

      VHL is an inherited suppressor syndrome that also causes nervous system tumors.

    2. What does VHL loss fail to account for?

      It causes hemangioblastomas and renal cancer through HIF, not skin pigment changes, neurofibromas or increased RAS-GTP.

  4. D. BRCA2-mediated homologous recombination (Why this does not fit)

    BRCA2 loss affects DNA double-strand break repair and does not explain café-au-lait macules with neurofibromas and high RAS-GTP.

    Reasoning steps for option D
    1. Why could a repair gene be considered in a young patient with multiple tumors?

      Inherited repair defects can cause cancers at young ages.

    2. Why does BRCA2 not explain the signaling result?

      BRCA2 repairs double-strand breaks and has no role in RAS GTP hydrolysis or the NF1 skin findings.

Takeaway: NF1 loss reduces neurofibromin-mediated restraint of RAS, increasing active RAS signaling.

Case sources: [6]

Case 17

A 27-year-old man develops progressive hearing difficulty. MRI shows bilateral vestibular schwannomas and two meningiomas. Genetic testing identifies a pathogenic variant in a tumor suppressor at 22q12.2. Which diagnosis and protein pairing is most accurate?

Show answer and explanations for case 17

  1. A. Neurofibromatosis type 1 with loss of neurofibromin (Why this does not fit)

    NF1 is at 17q11.2 and typically features café-au-lait macules, neurofibromas, and other NF1 manifestations rather than bilateral vestibular schwannomas.

    Reasoning steps for option A
    1. Why might NF1 be considered in a patient with nerve sheath tumors?

      Both neurofibromatosis types produce tumors of nerve sheath origin.

    2. Which locus and tumor pattern rule out NF1?

      NF1 is at 17q11.2 with café-au-lait macules and neurofibromas, while this patient has bilateral vestibular schwannomas and a 22q12.2 variant.

  2. B. Von Hippel-Lindau syndrome with loss of pVHL (Why this does not fit)

    VHL is associated with clear cell renal cancer and hemangioblastomas, not the specified NF2 locus and bilateral vestibular tumors.

    Reasoning steps for option B
    1. Why might VHL be considered for a young adult with intracranial tumors?

      VHL causes cerebellar hemangioblastomas, which are also posterior fossa tumors.

    2. What separates VHL from this presentation?

      VHL tumors are hemangioblastomas and renal cancers, not bilateral vestibular schwannomas with meningiomas.

  3. C. NF2-related schwannomatosis with impaired merlin function (Best answer)

    Bilateral vestibular schwannomas plus meningiomas and an NF2 variant at 22q12.2 identify NF2-related schwannomatosis and merlin loss.

    Reasoning steps for option C
    1. What do bilateral vestibular schwannomas and meningiomas point to?

      This combination is the hallmark of NF2-related schwannomatosis.

    2. Which protein is lost when the 22q12.2 suppressor is inactivated?

      Merlin, the NF2 product, whose loss removes growth restraint in Schwann and meningeal cells.

  4. D. Li-Fraumeni syndrome with loss of p53 (Why this does not fit)

    Li-Fraumeni has a broad early cancer spectrum and TP53 variants, not the 22q12.2 vestibular schwannoma pattern.

    Reasoning steps for option D
    1. Why could Li-Fraumeni syndrome be considered in a man with several tumors?

      Li-Fraumeni also causes multiple early tumors, including brain tumors.

    2. Which features point away from TP53?

      The variant is at 22q12.2, and bilateral vestibular schwannomas are not part of the TP53 spectrum.

Takeaway: Bilateral vestibular schwannomas are characteristic of NF2-related schwannomatosis caused by loss of merlin.

Case sources: [7]

Case 18

A 3-year-old child with bilateral aniridia and genitourinary anomalies is found to have a renal mass. Chromosomal testing shows a constitutional deletion at 11p13 that includes WT1 and PAX6. Which syndrome best integrates these findings?

Show answer and explanations for case 18

  1. A. Beckwith-Wiedemann spectrum from an 11p15 alteration (Why this does not fit)

    11p15-related overgrowth can predispose to Wilms tumor and hemihyperplasia, but it does not match the supplied 11p13 deletion with aniridia.

    Reasoning steps for option A
    1. Why might Beckwith-Wiedemann spectrum be considered in a child with a renal mass?

      11p15 alterations also predispose to Wilms tumor.

    2. Which findings do not match an 11p15 disorder?

      The child has aniridia, genitourinary anomalies and an 11p13 deletion, not overgrowth or hemihyperplasia.

  2. B. WAGR syndrome (Best answer)

    Aniridia, genitourinary abnormalities, Wilms tumor risk, and an 11p13 deletion involving WT1 and PAX6 define the WAGR framework.

    Reasoning steps for option B
    1. What does the combination of aniridia, genitourinary anomalies and a renal mass suggest?

      Wilms tumor, aniridia and genitourinary anomalies are the core of the WAGR pattern.

    2. How does the 11p13 deletion explain the whole phenotype?

      The deletion removes both WT1, raising Wilms tumor risk and affecting genitourinary development, and PAX6, whose loss causes aniridia.

  3. C. NF2-related schwannomatosis (Why this does not fit)

    NF2 is a 22q12.2 disorder associated with vestibular schwannomas and meningiomas, not aniridia with a renal tumor.

    Reasoning steps for option C
    1. Why might a schwannomatosis syndrome be considered in a child with a tumor predisposition?

      NF2 is also an inherited suppressor disorder that presents in childhood.

    2. What separates NF2 from this child?

      NF2 maps to chromosome 22 and causes nerve-sheath and meningeal tumors, while this child has aniridia, a kidney mass and an 11p13 deletion.

  4. D. MEN2 from an activating RET variant (Why this does not fit)

    MEN2 produces medullary thyroid carcinoma and pheochromocytoma, not the WT1-PAX6 deletion phenotype.

    Reasoning steps for option D
    1. Why could an inherited oncogene syndrome be considered for a childhood tumor?

      MEN2 is a germline cancer syndrome that can present early.

    2. Which findings exclude MEN2?

      MEN2 causes medullary thyroid carcinoma and pheochromocytoma, while this child has a WT1 and PAX6 deletion.

Takeaway: WAGR links an 11p13 deletion involving WT1 and PAX6 with Wilms tumor risk, aniridia, and genitourinary abnormalities.

Case sources: [15]

Case 19

An endometrial carcinoma has microsatellite instability. Sequencing shows an intact MLH1 coding region, but the MLH1 promoter contains dense CpG methylation and MLH1 messenger RNA is nearly absent. Which mechanism best explains loss of MLH1 function?

Show answer and explanations for case 19

  1. A. Activating point mutation that increases MLH1 enzymatic activity (Why this does not fit)

    The transcript is nearly absent, so increased enzymatic activity cannot explain the functional loss.

    Reasoning steps for option A
    1. Why might an activating change be considered in a tumor with an intact MLH1 coding region?

      Point variants are the most common way a single gene changes in cancer.

    2. What result excludes increased MLH1 enzyme activity?

      MLH1 messenger RNA is nearly absent, so little protein is made, which is loss of function.

  2. B. Gene amplification that raises MLH1 dosage (Why this does not fit)

    Amplification predicts increased copy number and often increased expression, opposite the reported absent transcript.

    Reasoning steps for option B
    1. Why might a copy-number change be considered when the coding sequence is normal?

      Amplification changes gene activity without altering the coding sequence.

    2. Why does amplification predict the wrong direction here?

      Extra copies usually raise expression, but MLH1 messenger RNA is nearly absent.

  3. C. A fusion kinase produced by chromosomal translocation (Why this does not fit)

    No fusion or kinase activity is described; the measured abnormality is promoter methylation with transcriptional loss.

    Reasoning steps for option C
    1. Why could a rearrangement be proposed in a tumor with microsatellite instability?

      Structural rearrangements can disrupt genes without point variants.

    2. What did testing actually find at MLH1?

      No fusion or kinase activity was seen, and the abnormality is dense promoter methylation with loss of transcript.

  4. D. Promoter hypermethylation silences transcription (Best answer)

    An intact coding sequence with dense promoter CpG methylation and absent transcript is direct evidence of epigenetic silencing.

    Reasoning steps for option D
    1. What do microsatellite instability and absent MLH1 messenger RNA show?

      The tumor has lost MLH1 mismatch repair function through failure of transcription.

    2. How does the promoter finding explain loss of MLH1 with a normal coding region?

      Dense CpG methylation of the promoter silences transcription, an epigenetic loss of function that needs no change in the coding sequence.

Takeaway: Promoter hypermethylation can silence a tumor suppressor or repair gene without changing its coding sequence.

Case sources: [4]

Case 20

A sarcoma carries one TP53 missense allele and one wild-type allele. Functional testing shows that mixed p53 tetramers containing the mutant subunit have markedly impaired DNA binding. Which observation best explains why a single missense allele can reduce p53 function before the wild-type allele is lost?

Show answer and explanations for case 20

  1. A. TP53 behaves only as a simple recessive enzyme in every tumor (Why this does not fit)

    The mixed-tetramer result directly shows that one mutant allele can interfere with the remaining wild-type product.

    Reasoning steps for option A
    1. Why is a recessive model a natural first assumption for TP53?

      TP53 is a tumor suppressor, and suppressors are classically recessive at the cell level.

    2. What does the tetramer assay show that the recessive model misses?

      Mixed tetramers with one mutant subunit bind DNA poorly, so the mutant allele interferes with the normal product.

  2. B. The mutant allele creates a BCR::ABL1 fusion (Why this does not fit)

    A TP53 missense variant does not create the Philadelphia fusion, and the assay specifically measures p53 tetramers.

    Reasoning steps for option B
    1. Why might a fusion be considered when a single allele changes tumor behavior?

      Fusion oncogenes act from one allele in a dominant way.

    2. Why does a Philadelphia fusion not apply here?

      The lesion is a TP53 missense variant measured in p53 tetramers, not a t(9;22) rearrangement.

  3. C. Dominant-negative interference in p53 tetramers (Best answer)

    The functional assay shows mutant-containing tetramers have impaired DNA binding, the defining logic of a dominant-negative effect.

    Reasoning steps for option C
    1. How does p53 bind DNA as a protein complex?

      p53 acts as a tetramer made of four subunits that together bind target DNA.

    2. Why does one missense allele reduce function before the normal allele is lost?

      Mutant subunits join the tetramer and impair DNA binding of the whole complex, which is a dominant-negative effect.

  4. D. The wild-type allele must be promoter-amplified (Why this does not fit)

    Amplification of the wild-type allele is neither reported nor able to explain mutant subunits disrupting mixed tetramers.

    Reasoning steps for option D
    1. Why might a change in the wild-type allele be proposed?

      Changes in the normal allele often matter in suppressor genes.

    2. What is wrong with invoking amplification of the normal allele?

      No amplification is reported, and extra normal copies would not explain mutant subunits disrupting mixed tetramers.

Takeaway: Tumor suppressor behavior can be more complex than a literal two-sequence-hit rule; mutant p53 can exert dominant-negative effects.

Case sources: [3]

Case 21

A woman with a germline pathogenic BRCA1 variant develops ovarian carcinoma. Her blood DNA contains one normal and one variant BRCA1 allele, but tumor DNA shows a large deletion that eliminates the chromosome segment carrying the normal allele. Which event occurred in the tumor?

Show answer and explanations for case 21

  1. A. Loss of heterozygosity at BRCA1 (Best answer)

    The tumor has lost the remaining normal allele that was present in constitutional DNA, which is the classic definition of loss of heterozygosity.

    Reasoning steps for option A
    1. What does comparing blood and tumor DNA show about the normal BRCA1 allele?

      Blood carries one normal and one variant allele, but the tumor has lost the segment carrying the normal allele.

    2. What is this event called, and why does it matter?

      It is loss of heterozygosity, and it leaves the tumor with only the variant BRCA1 allele and no homologous recombination backup.

  2. B. Oncogene amplification of BRCA1 (Why this does not fit)

    The tumor lost the normal BRCA1 segment rather than gaining extra copies or expression.

    Reasoning steps for option B
    1. Why might a copy-number change be considered when a chromosome segment is altered?

      Large genomic changes in tumors often involve amplification.

    2. Which direction does the tumor data show?

      The segment carrying the normal BRCA1 allele was deleted, a loss of copies rather than a gain.

  3. C. An activating RET germline event (Why this does not fit)

    RET activation causes MEN2 and does not explain tumor-specific loss of the normal BRCA1 allele.

    Reasoning steps for option C
    1. Why might a germline syndrome other than BRCA be considered in an inherited cancer?

      RET activation is a common example of an inherited cancer event.

    2. What separates RET activation from the tumor finding?

      RET causes MEN2 endocrine tumors, and it cannot explain deletion of the normal BRCA1 allele in ovarian carcinoma.

  4. D. A MYC immunoglobulin translocation (Why this does not fit)

    MYC rearrangement is a B-cell lymphoma mechanism and does not fit the chromosome-segment loss described here.

    Reasoning steps for option D
    1. Why could a translocation be proposed for a large chromosome change in a tumor?

      Translocations are major structural events that drive some cancers.

    2. Why does a MYC translocation not match this change?

      MYC-immunoglobulin rearrangements occur in B-cell lymphoma, while this tumor lost a chromosome segment carrying BRCA1.

Takeaway: Loss of heterozygosity can serve as a tumor-specific second event by eliminating the remaining functional suppressor allele.

Case sources: [1] [9]

Case 22

A 29-year-old man has a painless solid intratesticular mass. Serum AFP is normal, and orchiectomy shows a pure seminoma. A student argues that the diagnosis must be benign because the name ends in -oma. Which response is most accurate?

Show answer and explanations for case 22

  1. A. Every tumor ending in -oma is benign unless AFP is increased (Why this does not fit)

    Seminoma is malignant and may have normal AFP, so neither the suffix nor AFP establishes benignity.

    Reasoning steps for option A
    1. Why might a normal AFP seem reassuring about this testicular mass?

      AFP is a familiar marker of nonseminomatous germ cell tumors.

    2. Why do neither the suffix nor a normal AFP show that the tumor is benign?

      Pure seminoma does not make AFP, and seminoma is malignant regardless of how its name ends.

  2. B. Seminoma is a malignant testicular germ cell tumor despite the suffix (Best answer)

    NCI classifies seminoma among malignant testicular germ cell tumors; the suffix alone cannot determine biologic behavior.

    Reasoning steps for option B
    1. What does orchiectomy show about the tumor type?

      The pathology is pure seminoma, a testicular germ cell tumor.

    2. How should the student's suffix argument be answered?

      Seminoma is malignant at diagnosis, like lymphoma and melanoma, so the ending of a tumor name does not define its behavior.

  3. C. Seminoma becomes malignant only after it metastasizes (Why this does not fit)

    Seminoma is already a malignant germ cell tumor at diagnosis; metastasis changes stage, not the basic malignant classification.

    Reasoning steps for option C
    1. Why might metastasis seem to be the marker of malignancy?

      Spread to distant sites is the most obvious sign of malignant behavior.

    2. How does metastasis relate to the classification of seminoma?

      Seminoma is malignant when it is diagnosed, and spread changes the stage rather than the diagnosis.

  4. D. The mass is malignant only if β-hCG is increased (Why this does not fit)

    Seminoma can be malignant with or without increased β-hCG, and the pathology diagnosis determines the tumor type.

    Reasoning steps for option D
    1. Why could a raised hormone marker seem to prove malignancy in a testicular mass?

      Some seminomas and other germ cell tumors secrete β-hCG, which clinicians follow.

    2. Why is a normal or raised β-hCG not the deciding factor?

      Markers help with staging and follow-up, but many pure seminomas secrete no β-hCG; the orchiectomy histology has already made this a malignant germ cell tumor.

Takeaway: Tumor nomenclature has historical exceptions; -oma cannot be used as a universal benignity rule.

Case sources: [18]

Case 23

A 68-year-old man had a right-sided colon adenocarcinoma resected 2 years ago. Surveillance imaging now shows six new liver lesions. Biopsy of one lesion resembles the prior colon tumor and is CDX2 positive. He has no cirrhosis or chronic viral hepatitis. Which interpretation best fits the new liver findings?

Show answer and explanations for case 23

  1. A. New primary hepatocellular carcinoma in a noncirrhotic liver (Why this does not fit)

    Hepatocellular carcinoma is possible without cirrhosis, but the matching colon morphology and CDX2 positivity strongly support metastatic colorectal origin.

    Reasoning steps for option A
    1. Why is hepatocellular carcinoma still worth considering without cirrhosis?

      It can arise in a noncirrhotic liver, and a new liver mass always raises the question.

    2. Which biopsy findings favor colorectal origin instead?

      The lesion resembles the prior colon tumor and is CDX2 positive, an intestinal marker not expected in hepatocellular carcinoma.

  2. B. Benign focal nodular hyperplasia in multiple sites (Why this does not fit)

    Focal nodular hyperplasia would not reproduce the prior adenocarcinoma morphology or the intestinal tumor immunophenotype.

    Reasoning steps for option B
    1. Why might a benign lesion be considered for several liver masses?

      Focal nodular hyperplasia is a common benign liver mass that can be multiple.

    2. What in the biopsy excludes focal nodular hyperplasia?

      The tissue is malignant adenocarcinoma matching the prior colon tumor, with intestinal CDX2 staining.

  3. C. Metastatic colorectal adenocarcinoma to the liver (Best answer)

    The known colon primary, multifocal liver distribution, matching morphology, and intestinal immunophenotype together support metastatic colorectal cancer.

    Reasoning steps for option C
    1. What do the history and imaging suggest before the biopsy result?

      A resected colon adenocarcinoma followed by six new liver lesions is a common pattern of portal venous metastasis.

    2. How does the biopsy confirm the source?

      Matching colon morphology and CDX2 positivity show intestinal origin, so the lesions are metastatic colorectal adenocarcinoma.

  4. D. Primary seminoma of the liver (Why this does not fit)

    Seminoma is a germ cell tumor and does not match the prior colon adenocarcinoma or CDX2-positive morphology.

    Reasoning steps for option D
    1. Why might a germ cell tumor be considered in an unusual site?

      Germ cell tumors can occasionally arise outside the gonads.

    2. Why does seminoma fail to fit the biopsy?

      The lesion is an adenocarcinoma resembling the colon primary and is CDX2 positive, not a germ cell tumor.

Takeaway: Classify a distant lesion using the known primary, distribution, morphology, and molecular or immunophenotypic evidence rather than an organ shortcut.

Case sources: [17]

Case 24

A colonic epithelial clone carries one inactivating APC allele but retains one functional APC copy and has normal cytoplasmic β-catenin regulation. Months later, the remaining APC allele is deleted and nuclear β-catenin rises. Which change best explains the new phenotype?

Show answer and explanations for case 24

  1. A. The deletion directly activates a constitutive ABL kinase (Why this does not fit)

    ABL fusion kinase activation requires a specific rearrangement and is unrelated to the observed APC-β-catenin transition.

    Reasoning steps for option A
    1. Why might a kinase event be considered when a deletion changes cell behavior?

      Chromosomal changes can create activated kinases such as ABL fusions.

    2. Why does the deletion here not create an ABL kinase?

      ABL activation needs a specific rearrangement with BCR, while this change removes the remaining APC allele and raises nuclear β-catenin.

  2. B. The deletion increases neurofibromin activity and lowers RAS-GTP (Why this does not fit)

    APC loss does not increase NF1 function; the measured consequence is nuclear β-catenin accumulation.

    Reasoning steps for option B
    1. Why might RAS signaling be considered in a colonic clone that becomes more abnormal?

      RAS pathway changes do contribute to adenoma progression.

    2. What is wrong with raised neurofibromin after APC deletion?

      Losing APC does not increase NF1 activity, and the measured change is nuclear β-catenin, not lower RAS-GTP.

  3. C. The deletion restores homologous recombination through BRCA1 (Why this does not fit)

    Losing APC cannot restore BRCA1-dependent repair, and the reported readout is Wnt pathway activation.

    Reasoning steps for option C
    1. Why could DNA repair be considered when a colonic clone gains a new genetic event?

      Repair failure lets clones collect further genetic changes.

    2. Why can APC deletion not restore BRCA1 repair?

      Losing a suppressor does not restore an unrelated repair pathway, and the readout is Wnt activation.

  4. D. Loss of remaining APC activates Wnt transcription (Best answer)

    The before-and-after data show preserved control with one functional copy, then β-catenin accumulation after the remaining APC copy is lost.

    Reasoning steps for option D
    1. What does the first observation show about a single functional APC copy?

      With one working APC allele, cytoplasmic β-catenin regulation was still normal.

    2. What changes after the remaining APC allele is deleted?

      No APC is left to target β-catenin for destruction, so it moves to the nucleus and activates Wnt target transcription.

Takeaway: A classic suppressor can show a functional threshold: loss of the remaining useful allele can produce the pathway phenotype.

Case sources: [1] [10]

Case 25

A woman with a BRCA1-deficient ovarian carcinoma is treated with a PARP inhibitor. Tumor cells accumulate DNA lesions they cannot repair efficiently, while normal cells with intact BRCA1 retain homologous recombination capacity. Which concept best explains the selective vulnerability of the tumor?

Show answer and explanations for case 25

  1. A. BRCA1-PARP synthetic lethality (Best answer)

    The tumor already lacks effective BRCA1-dependent homologous recombination, so blocking a compensatory repair process creates a combination the cancer cell tolerates poorly.

    Reasoning steps for option A
    1. What does the tumor already lack before treatment?

      Its BRCA1 deficiency leaves little homologous recombination to repair double-strand breaks.

    2. Why does PARP inhibition harm tumor cells more than normal cells?

      Blocking PARP adds a second repair failure that the BRCA1-deficient cells cannot survive, while normal cells use intact homologous recombination, which is synthetic lethality.

  2. B. Activation of RET signaling by the PARP inhibitor (Why this does not fit)

    RET is a receptor tyrosine kinase linked to MEN2 and does not explain the repair-selective response.

    Reasoning steps for option B
    1. Why might a signaling change be proposed for a drug response?

      Some cancer drugs work through receptor tyrosine kinase pathways.

    2. What result points away from RET?

      The selective effect depends on a repair defect in BRCA1-deficient cells, and RET is an MEN2 receptor unrelated to PARP.

  3. C. Restoration of APC function through β-catenin accumulation (Why this does not fit)

    β-catenin accumulation reflects loss of APC function with Wnt pathway activation, not restoration of a missing DNA-repair pathway.

    Reasoning steps for option C
    1. Why might a suppressor pathway be linked to a selective drug effect?

      APC is a familiar suppressor, and β-catenin changes are common in tumors.

    2. Why is restoring APC through β-catenin backwards?

      β-catenin accumulates when APC is lost, and neither event repairs DNA in a BRCA1-deficient tumor.

  4. D. Creation of the Philadelphia chromosome during treatment (Why this does not fit)

    BCR::ABL1 arises from a specific chromosomal rearrangement and is unrelated to PARP inhibition in a BRCA1-deficient tumor.

    Reasoning steps for option D
    1. Why might a new chromosomal rearrangement be blamed for a treatment effect?

      Therapy can sometimes induce new genetic changes in cells.

    2. Why does the Philadelphia chromosome not explain the tumor vulnerability?

      BCR::ABL1 is a myeloid leukemia rearrangement and has no role in the repair-selective response to PARP inhibition.

Takeaway: BRCA-deficient tumors can be vulnerable to PARP inhibition through synthetic lethality, reflecting dependence on alternate repair processes.

Case sources: [9]

Feedback or correction

Sources

  1. Cancer genome landscapes (2013-03-29)

    General framework for driver genes, oncogene activation, tumor suppressor loss, copy-number change, and pathway interpretation.

    Return 1.1 Return 1.2 Return 1.3 Return 1.4 Return 1.5 Return 1.6 Return 1.7 Return 1.8 Return 1.9 Return 1.10 Return 1.11 Return 1.12 Return 1.13 Return 1.14

  2. Mutation and cancer: statistical study of retinoblastoma (1971-04)

    Original statistical basis for the retinoblastoma two-hit model.

    Return 2.1 Return 2.2 Return 2.3 Return 2.4 Return 2.5 Return 2.6

  3. Should mutant TP53 be targeted for cancer therapy?

    TP53 mutation frequency and the distinction among loss of function, dominant-negative effects, and acquired mutant activities.

    Return 3.1 Return 3.2 Return 3.3 Return 3.4 Return 3.5 Return 3.6

  4. DNA methylation and histone variants in aging and cancer (2021)

    Age-associated methylome changes and epigenetic silencing in cancer.

    Return 4.1 Return 4.2 Return 4.3

  5. Retinoblastoma - GeneReviews (2023-09-21)

    Heritable versus nonheritable retinoblastoma, laterality, age, and RB1 testing framework.

    Return 5.1 Return 5.2 Return 5.3 Return 5.4 Return 5.5 Return 5.6 Return 5.7 Return 5.8

  6. Neurofibromatosis 1 - GeneReviews (2025-04-03)

    NF1 phenotype, 17q11.2 locus, neurofibromin, and RAS regulation.

    Return 6.1 Return 6.2 Return 6.3

  7. NF2-Related Schwannomatosis - GeneReviews (2023-04-20)

    Current NF2 terminology, bilateral vestibular schwannomas, merlin, and 22q12.2.

    Return 7.1 Return 7.2

  8. Von Hippel-Lindau Syndrome - GeneReviews (2025-05-01)

    VHL phenotype, clear cell renal cell carcinoma, hemangioblastomas, and HIF-related biology.

    Return 8.1 Return 8.2 Return 8.3

  9. BRCA1- and BRCA2-Associated Hereditary Breast and Ovarian Cancer - GeneReviews (2026-03-25)

    BRCA1/2 cancer spectrum, inherited risk, and homologous-recombination related management context.

    Return 9.1 Return 9.2 Return 9.3 Return 9.4 Return 9.5 Return 9.6

  10. APC-Associated Polyposis Conditions - GeneReviews (2022-05-12)

    APC, familial adenomatous polyposis, adenoma burden, and colorectal cancer risk.

    Return 10.1 Return 10.2 Return 10.3 Return 10.4

  11. Mechanisms of resistance to BCR-ABL TKIs and the therapeutic strategies: A review (2015-03)

    BCR::ABL1 fusion, Philadelphia chromosome, and constitutive tyrosine kinase biology in CML.

    Return 11.1 Return 11.2 Return 11.3

  12. MYC-driven aggressive B-cell lymphomas: biology, entity, differential diagnosis and clinical management (2015)

    MYC locus and rearrangement biology in Burkitt and other aggressive B-cell lymphomas.

    Return 12.1 Return 12.2 Return 12.3

  13. Multiple Endocrine Neoplasia Type 2 - GeneReviews (2023-08-10)

    RET activation and MEN2 phenotype.

    Return 13.1 Return 13.2

  14. The biology and treatment of EML4-ALK non-small cell lung cancer (2010)

    EML4::ALK fusion as an oncogenic driver in a subset of lung cancers.

    Return 14.1 Return 14.2 Return 14.3

  15. Wilms Tumor Predisposition - GeneReviews

    WT1-related Wilms tumor predisposition, WAGR at 11p13, and distinction from 11p15-related overgrowth syndromes.

    Return 15.1 Return 15.2

  16. Basic mechanisms of high-risk human papillomavirus-induced carcinogenesis: roles of E6 and E7 proteins (2007-10)

    High-risk HPV E6 effects on p53 and E7 effects on pRB/E2F control.

    Return 16.1 Return 16.2

  17. Metastatic Cancer: When Cancer Spreads

    Official overview of metastasis and common organ-specific metastatic patterns.

    Return 17.1 Return 17.2 Return 17.3

  18. Testicular Cancer Treatment (PDQ): Health Professional Version

    Official NCI classification of seminoma as a malignant testicular germ cell tumor.

    Return 18.1 Return 18.2

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