Cancer Pathology

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    Step 1 Cancer — Quick Reference
    Rule: Know translocation → fusion/product → cancer → drug. Most fusions create constitutively active kinases or aberrant transcription factors.
    TranslocationFusion / EffectCancerDrug / Note
    t(9;22)BCR-ABL p210 — constitutive TKCML; also Ph+ ALL (p190)Imatinib, dasatinib, ponatinib (T315I)
    t(15;17)PML-RARα — blocks myeloid differentiationAML-M3 (APL); DICATRA + arsenic trioxide
    t(8;21)AML1-ETO (RUNX1-RUNX1T1)AML-M2Good prognosis; high-dose AraC
    inv(16)/t(16;16)CBFβ-MYH11AML-M4Eo; abnormal eosGood prognosis
    t(8;14)c-MYC to IgH; MYC overexpressionBurkitt lymphomaStarry sky; Ki-67 ~100%
    t(2;8), t(8;22)c-MYC to Igκ or IgλBurkitt variantsSame biology as t(8;14)
    t(14;18)BCL-2 to IgH; blocks apoptosisFollicular lymphomaMost common adult NHL; indolent
    t(11;14)Cyclin D1 overexpressionMantle cell lymphomaCD5+, CD23−; poor prognosis
    t(2;5)NPM-ALK — constitutive ALK kinaseALCL (T-cell)CD30+; crizotinib
    t(11;22)(q24;q12)EWSR1-FLI1 — aberrant TFEwing sarcomaDiaphysis; onion-skin; small blue cells
    t(X;18)SS18-SSX1/2 — aberrant repressorSynovial sarcomaBiphasic; near joints; TLE1+
    t(12;21)TEL-AML1 (ETV6-RUNX1)Pediatric B-ALLBest prognosis ALL; cryptic
    t(4;11)MLL-AF4Infant ALL (<1yr)Worst pediatric ALL prognosis
    t(1;19)E2A-PBX1Pre-B ALLIntermediate prognosis
    t(9;22) in ALLBCR-ABL p190Ph+ ALL (adult)Poor; TKI + chemo
    t(3;8) / RET/PTCRET/PTC rearrangementsPapillary thyroid carcinomaAlso BRAF V600E (point mut)
    t(2;3)(q13;p25)PAX8-PPARγFollicular thyroid carcinomaFNA cannot diagnose FTC alone
    inv(3)/t(3;3)GATA2 enhancer → EVI1 overexpressionAML; adverse riskThrombocytosis; dysplastic megas
    t(6;9)DEK-NUP214AML; adverse riskBasophilia; FLT3-ITD co-mutation >70%
    t(5;12)TEL-PDGFRB (ETV6-PDGFRB)CEL / MPN with eosinophiliaExquisitely imatinib-sensitive
    t(11;22) EWSR1-WT1Polyphenotypic fusion TFDSRCTYoung males; abdominal; poor prognosis
    Alkylator-related secondary AML-5/del(5q), -7/del(7q)t-MDS/AMLLatency 4-8yr; poor prognosis
    Topo II-related secondary AMLMLL (11q23) or RUNX1 (21q22) balanced translocationst-AMLLatency 1-3yr; anthracyclines, etoposide
    Rule: Markers monitor treatment response — not screen (exception: AFP in cirrhosis surveillance). Know false-positive causes — they appear as distractors.
    MarkerCancer(s)Important False PositivesKey Notes
    AFPHCC, yolk sac tumor, hepatoblastomaPregnancy, acute hepatitis flare, cirrhosisANY AFP in GCT = non-seminomatous element; >400 = HCC diagnosis in cirrhosis+LI-RADS5
    β-hCGChoriocarcinoma, hydatidiform mole, mixed GCTPregnancy, marijuanaSeminoma: AFP must = 0; any AFP = non-seminomatous
    CEAColorectal, gastric, pancreatic, lung, breastSmoking (most important), IBD, cirrhosis, pancreatitisMain use: monitor CRC recurrence post-resection; not for diagnosis
    CA-125Serous ovarian, endometrialEndometriosis, menstruation, pregnancy, cirrhosis, PIDNot a screening test; monitor recurrence
    CA 19-9Pancreatic, cholangiocarcinoma, gastricBiliary obstruction (critical!), pancreatitis, PSCUnreliable when jaundiced; Lewis antigen-negative → false negative
    CA 15-3 / CA 27.29Breast cancerBenign breast disease, liver diseaseMarker flare: transient rise with effective therapy — do not change treatment
    PSAProstate cancerBPH, prostatitis, recent ejaculation/DREBCR post-prostatectomy: PSA ≥0.2 ng/mL × 2; PSADT <3mo = systemic disease
    CalcitoninMedullary thyroid carcinomaHypercalcemia (other causes)Screen MEN2A/2B families; prophylactic thyroidectomy
    ThyroglobulinPapillary, follicular thyroid carcinomaBenign thyroid diseaseShould be undetectable after total thyroidectomy + RAI; any rise = recurrence
    5-HIAA (urine)Carcinoid tumorSerotonin-rich foods, SSRIsCarcinoid syndrome only with liver mets (bypasses first-pass metabolism)
    LDHLymphoma, testicular GCT (staging)Hemolysis, MI, liver disease, PENon-specific but prognostic in lymphoma; elevated in dysgerminoma
    Inhibin A/BGranulosa cell tumor (ovarian)FOXL2 mutation; Call-Exner bodies; estrogen → endometrial hyperplasia
    CD15+, CD30+Reed-Sternberg cells (Hodgkin lymphoma)EXCEPTION: LPHL = CD20+, CD15−, CD30−
    CLL phenotypeCLL: CD5+, CD19+, CD20(dim)+, CD23+vs Mantle cell: CD5+, CD19+, CD23−, Cyclin D1+
    HCL phenotypeHCL: CD11c+, CD25+, CD103+, TRAP+BRAF V600E; cladribine; dry tap on biopsy
    SCLC is the king of paraneoplastic syndromes. When you see SCLC — think SIADH, ectopic ACTH, Lambert-Eaton, cerebellar degeneration, limbic encephalitis.
    SyndromeCancerMediator / AntibodyKey Distinguishing Feature
    SIADHSCLCEctopic ADHHyponatremia, euvolemic; urine Na >20, concentrated urine
    Ectopic ACTH (Cushing)SCLC, carcinoid, MTC, thymomaEctopic ACTH → bilateral adrenal hyperplasia↓K+, HTN, hyperglycemia; no dex suppression
    Lambert-Eaton (LEMS)SCLCAnti-P/Q-type VGCCWeakness IMPROVES with repetition; ↓DTRs. Opposite of MG
    Myasthenia gravisThymomaAnti-AChRWeakness WORSENS with repetition; ptosis, diplopia
    Hypercalcemia of malignancySCC lung, RCC, breast, MMPTHrP (most common)↑Ca, ↓PO4, ↓PTH (distinguishes from hyperPTH)
    Cerebellar degenerationSCLC, breast, ovarianAnti-Yo (anti-Purkinje), Anti-HuTruncal ataxia, dysarthria, nystagmus
    Limbic encephalitisSCLC, testicular teratomaAnti-Hu, anti-NMDARMemory loss, seizures, psychiatric sx
    Trousseau syndromePancreatic, GI, lungTumor mucin activates clottingMigratory superficial thrombophlebitis
    DermatomyositisOvarian, lung, GI, breastAutoimmune; anti-Mi-2Heliotrope rash, Gottron papules, ↑CK
    Carcinoid syndromeCarcinoid with LIVER METSSerotonin, bradykininDAFE: Diarrhea, wheezing, Flushing, right-sided Endocardial disease
    ErythrocytosisRCC, HCC, hemangioblastomaEctopic EPO (HIGH EPO)vs PV: LOW EPO + JAK2 V617F in PV
    Nephrotic syndrome (MCD)Hodgkin lymphomaLymphokine damage to GBMFoot process effacement; no immune deposits
    Oncogenes = dominant (1 hit). Tumor suppressors = recessive (2 hits, Knudson). Loss of TSG function → cancer. Gain of oncogene function → cancer.
    Key Oncogenes
    GeneTypeCancerDrug / Notes
    KRASGTPase (signal)Pancreatic (90%), CRC, lungKRAS G12C → sotorasib/adagrasib; mutant = anti-EGFR resistant
    HER2/ERBB2RTK — amplifiedBreast (25%), gastric, ovarianTrastuzumab; T-DXd; monitor for cardiomyopathy
    EGFRRTK — mutatedNSCLC adenocarcinomaExon 19 del / L858R → osimertinib; T790M = resistance
    ALK fusionsRTK — fusionNSCLC (3%), ALCLEML4-ALK in lung; crizotinib/alectinib
    RETRTK — mutation/fusionMTC (MEN2), papillary thyroid, NSCLCSelpercatinib/pralsetinib; prophylactic thyroidectomy in MEN2
    BCL-2Anti-apoptoticFollicular lymphoma (t(14;18)), CLLVenetoclax targets BCL-2
    BRAF V600ESer/Thr kinaseMelanoma (50%), papillary thyroid, HCL, CRC (right-sided)Dabrafenib + trametinib; BRAF mut CRC = poor prognosis; rules out Lynch
    JAK2 V617FNon-receptor TKPV (>95%), ET, PMFRuxolitinib; JAK-STAT pathway
    c-MYC / N-MYCTranscription factorBurkitt (c-MYC); Neuroblastoma (N-MYC amplification)N-MYC ≥10 copies = poor prognosis neuroblastoma
    KIT (CD117)RTK — mutatedGIST, AML-M3, mastocytosisImatinib for GIST; PDGFRA D842V = imatinib resistant → avapritinib
    Key Tumor Suppressors
    Gene (Chr)Cancer / SyndromeFunction
    TP53 (17p13)Most cancers; Li-Fraumeni syndromep21 activation → G1 arrest; BAX → apoptosis; MDM2 degrades p53
    RB1 (13q14)Retinoblastoma, osteosarcoma, SCLCBinds E2F; CDK4/6 + CycD phosphorylates RB → releases E2F → S phase
    BRCA1 (17q21)Breast (70%), ovarian, prostateHomologous recombination repair; PARP inhibitor synthetic lethality
    BRCA2 (13q12)Breast, ovarian, pancreatic, MALE breastHR repair; BRCA2 unique: male breast ca, pancreatic ca
    APC (5q21)FAP → CRC; desmoidsDegrades β-catenin (Wnt OFF); loss → nuclear β-catenin → MYC, Cyclin D1
    MLH1/MSH2/MSH6/PMS2Lynch syndrome (HNPCC) → CRC, endometrialMismatch repair; MSI-H; BRAF WT in Lynch (BRAF mut = sporadic)
    VHL (3p25)Clear cell RCC, hemangioblastoma, pheochromocytomaDegrades HIF-1α; VHL loss → ↑VEGF + EPO
    PTEN (10q23)Endometrial, prostate, breast; Cowden syndromeOpposes PI3K/AKT; loss → ↑AKT survival signaling
    NF1 (chr 17) / NF2 (chr 22)NF1: neurofibromas, MPNST; NF2: bilateral acoustic neuromasNF1 = RAS-GAP (inactivates RAS); NF2 = merlin (cytoskeleton)
    WT1 (11p13)Wilms tumor; WAGR, Denys-DrashRenal/gonadal TF; two-hit model
    Step 1 photo question strategy: See the buzzword → name the cancer → know the molecular alteration. These pairs are tested by image recognition.
    Starry sky patternBurkitt lymphoma. Tingible-body macrophages eating apoptotic cells. Ki-67 ~100%.
    Owl-eye nucleoliReed-Sternberg cells in Hodgkin lymphoma. Also CMV intranuclear inclusions (different context).
    Psammoma bodiesPSaMMa: Papillary thyroid, Serous ovarian, Mesothelioma, Meningioma. Concentric calcifications.
    Keratin pearlsSquamous cell carcinoma (any site). Well-differentiated SCC.
    Signet ring cellsDiffuse gastric adenocarcinoma (linitis plastica). Mucin displaces nucleus. → Krukenberg tumor if ovarian mets.
    Pseudopalisading necrosisGlioblastoma (WHO Grade IV). Tumor cells radiate around necrotic center.
    Orphan Annie eye nucleiPapillary thyroid carcinoma. Ground-glass empty nuclei + intranuclear pseudoinclusions + nuclear grooves.
    Rosenthal fibersPilocytic astrocytoma (children, cerebellum). BRAF-KIAA1549 fusion. Also Alexander disease.
    Homer Wright rosettesMedulloblastoma, Neuroblastoma, PNET. NO central lumen; tumor cells around neuropil.
    Flexner-Wintersteiner rosettesRetinoblastoma. HAS central lumen (photoreceptor attempt).
    Auer rodsAML (especially M3 = faggot cells = bundles). NEVER in ALL.
    Call-Exner bodiesGranulosa cell tumor (ovarian). Estrogen → endometrial hyperplasia. FOXL2 mutation. Inhibin+.
    Schiller-Duval bodiesYolk sac tumor. AFP markedly elevated. Glomeruloid structure.
    Birbeck granules (tennis racket)Langerhans cell histiocytosis. CD1a+, S-100+, CD207+. BRAF V600E ~50%.
    Fried egg cellsOligodendroglioma. Perinuclear halo artifact. IDH mut + 1p/19q co-del = best glioma prognosis.
    Onion-skin periosteal reactionEwing sarcoma. Diaphysis. t(11;22) EWSR1-FLI1.
    Sunburst + Codman triangleOsteosarcoma. Metaphysis of long bones. Adolescents. MAP chemotherapy.
    Hairy cytoplasmic projectionsHairy cell leukemia. TRAP+, BRAF V600E. Cladribine. Dry tap on biopsy.
    Oat cells + crush artifactSCLC. Neuroendocrine; chromogranin+, synaptophysin+. Most paraneoplastic syndromes.
    Congo red + apple-green birefringenceAmyloidosis (AL most common in myeloma context). Macroglossia, periorbital purpura.
    Step 1 loves pairing a drug with its unique toxicity and antidote/prevention. Memorize the highlighted pairs.
    DrugMechanismUnique ToxicityAntidote / Prevention
    MethotrexateDHFR inhibitor → ↓THF (S-phase)Mucositis, myelosuppression, nephrotoxicity (high dose)Leucovorin (folinic acid)
    5-FUThymidylate synthase inhibitor (S-phase)Hand-foot syndrome, mucositis; DPD deficiency → fatal toxicityLeucovorin enhances efficacy
    CyclophosphamideAlkylating agent (non-cycle specific)Hemorrhagic cystitis (acrolein metabolite)MESNA + IV hydration
    BusulfanAlkylating agentPulmonary fibrosis, hyperpigmentation, seizuresPhenytoin (seizure prophylaxis)
    CisplatinPlatinum cross-links (non-cycle)Nephrotoxicity, ototoxicity, neuropathyIV hydration, amifostine
    CarboplatinPlatinum (non-cycle)Primarily myelosuppression; less nephro/oto than cisplatinDose by AUC (Calvert formula)
    OxaliplatinPlatinum (non-cycle)Cumulative sensory neuropathy (cold-triggered initially)Used in CRC (FOLFOX, CAPOX)
    BleomycinFree radical DNA breaks (G2)Pulmonary fibrosis; worsened by high FiO2Low FiO2; monitor PFTs
    DoxorubicinTopo II inhibitor + free radicalsDilated cardiomyopathy (cumulative, irreversible)Dexrazoxane; lifetime limit ~550 mg/m²
    VincristineTubulin polymerization block (M-phase)Peripheral neuropathy + constipation; minimal marrow"Vincristine = nerves"
    VinblastineTubulin polymerization block (M-phase)Myelosuppression (dose-limiting)"Vinblastine = blood"
    PaclitaxelMicrotubule stabilization (M-phase)Myelosuppression, neuropathy; hypersensitivity (Cremophor)Pre-medicate: dex + antihistamine
    IrinotecanTopoisomerase I inhibitorEarly (cholinergic) diarrhea + late (secretory) diarrheaEarly → Atropine; Late → Loperamide
    EtoposideTopoisomerase II inhibitorMyelosuppression; secondary AML (MLL translocation)Latency 1-3 years
    ATRADifferentiates APL cells via PML-RARαDifferentiation syndrome: fever, pulm infiltrates, renal failureDexamethasone; do NOT stop ATRA
    TamoxifenSERM (ER antagonist in breast)Endometrial cancer; DVT/PE; hot flashesAIs preferred postmenopause (no uterine risk)
    6-MercaptopurinePurine synthesis inhibitor (S-phase)Myelosuppression, hepatotoxicityReduce dose 75% if on allopurinol (blocks XO → ↑6-MP)
    AsparaginaseDepletes asparagine (G1-specific)Pancreatitis, coagulopathy (↓fibrinogen, ↓AT-III)Pediatric ALL (PEGylated = pegaspargase)
    MEN Syndromes
    SyndromeComponentsGeneKey Rule
    MEN1Parathyroid (90%) + Pituitary (prolactinoma) + Pancreas (gastrinoma)MEN1 (menin), 11q13"3 Ps": Parathyroid, Pituitary, Pancreas
    MEN2AMTC (100%) + Pheo (50%) + Parathyroid (20%)RET, codon 634Rule out pheo BEFORE thyroid surgery
    MEN2BMTC (most aggressive) + Pheo + Mucosal neuromas + Marfanoid habitusRET M918T (de novo)NO parathyroid; most aggressive MTC
    Hereditary Cancer Syndromes
    SyndromeGene / ChrCancersDistinguishing Feature
    FAPAPC, 5q21CRC (100% by 40s)>100 polyps; prophylactic colectomy; Gardner = desmoids + osteomas
    Lynch (HNPCC)MLH1/MSH2/MSH6/PMS2CRC (right-sided), endometrial, ovarian, urinary tractMSI-H; BRAF WT rules OUT Lynch
    Peutz-JeghersSTK11/LKB1GI, breast, pancreatic, gynecologicPerioral melanin spots; hamartomatous polyps
    Li-FraumeniTP53Sarcomas, breast, brain, adrenal, leukemiaGermline TP53; early onset; SBLA mnemonic
    VHLVHL, 3p25Clear cell RCC, hemangioblastoma, pheoVHL loss → ↑HIF-1α → ↑VEGF + EPO
    CowdenPTEN, 10q23Breast, follicular thyroid, endometrialHamartomas; macrocephaly; PTEN opposes PI3K
    GorlinPTCH1Multiple BCCs, medulloblastoma (desmoplastic)Jaw cysts, calcified falx; vismodegib for BCC
    NF-1NF1, chr 17Neurofibromas, MPNST, optic glioma≥6 café-au-lait spots; Lisch nodules; axillary freckling; NF1 = RAS-GAP
    NF-2NF2, chr 22Bilateral acoustic neuromas, meningiomas, ependymomas"22 = 2 ears"
    HDGCCDH1 (E-cadherin)Diffuse gastric cancer (70%), lobular breast caProphylactic total gastrectomy; occult signet ring cells
    Metastasis pattern mnemonics: Osteoblastic = "Prostate Blasts into Bone." Osteolytic = MM, RCC, Thyroid. BLT with Ketchup = Breast, Lung, Thyroid, Kidney, Prostate go to bone.
    OrganTop Primary SourcesKey Feature
    BoneBreast, Lung, Thyroid, Kidney, ProstateBlastic (prostate) vs Lytic (MM — no alk phos rise, RCC, thyroid); pathologic fractures
    BrainLung (#1 overall), Breast, Melanoma, RCC, ColonGray-white junction; multiple lesions; melanoma = most hemorrhagic
    LiverCRC (#1 in US), pancreatic, gastric, breast, carcinoidCarcinoid liver mets → carcinoid syndrome; multiple nodules
    Lung (cannonball mets)RCC, choriocarcinoma, sarcoma, CRC, breastRound, well-defined; RCC and choriocarcinoma = hemorrhagic
    Ovary (Krukenberg)Gastric (most common), CRC, breast (lobular), appendicealBilateral; signet ring cells; mucin-secreting
    Spinal cordBreast, lung, prostate (extradural, most common)EMERGENCY: immediate dexamethasone + STAT MRI; radiation ± surgery
    Left supraclavicular nodeGI (gastric, pancreatic, colon), pelvicVirchow's node (Troisier sign): thoracic duct drains abdominal viscera → left subclavian junction
    Umbilical noduleGI (gastric, pancreatic, colon), ovarianSister Mary Joseph nodule; falciform ligament spread; indicates Stage IV
    AdrenalLung (#1), breast, melanoma, RCCBilateral adrenal masses → mets until proven otherwise; adrenal insufficiency if bilateral
    Oncologic Emergencies
    EmergencyPresentationImmediate Treatment
    Spinal cord compressionBack pain + bilateral leg weakness + bowel/bladder dysfunctionHigh-dose dexamethasone IMMEDIATELY → STAT MRI → radiation ± surgery
    SVC syndromeFacial/arm edema, neck vein distension, facial cyanosisHOB elevation, steroids, radiation (SCLC/NHL), stenting
    Tumor lysis syndrome↑K, ↑PO4, ↑uric acid, ↓Ca after chemo (Burkitt, ALL)IV hydration, allopurinol/rasburicase; monitor electrolytes
    Febrile neutropeniaTemp ≥38.3°C + ANC <500Blood cultures → IV antibiotics (cefepime) within 60 minutes
    Hypercalcemia of malignancyConfusion, polyuria, constipation, Ca >12IV saline → zoledronic acid → calcitonin (bridge) → denosumab if refractory
    LeukostasisWBC >100k + confusion + pulmonary infiltratesLeukapheresis + hydroxyurea; avoid RBC transfusion