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Neoplasia - Robbins Pathology Notes

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1. Definitions

• Neoplasia: "New growth" - an abnormal mass of tissue whose growth exceeds and is uncoordinated with that of normal tissues and persists in the same excessive manner after cessation of the stimuli that evoked it.
• Tumor: Originally meant any swelling; now used synonymously with neoplasm.
• Oncology: Study of tumors (Greek: onkos = tumor).

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2. Nomenclature

Benign Tumors

Malignant Tumors

Special/Mixed Tumors

• Teratoma: Contains elements of all 3 germ layers (ecto, meso, endoderm); arises from totipotent cells (gonads, mediastinum, sacrococcygeal region).
• Hamartoma: Disorganized overgrowth of mature tissues indigenous to the site (NOT a true neoplasm).
• Choristoma: Ectopic normal tissue (e.g., pancreatic tissue in gastric wall).
• Blastoma: Tumors resembling embryonal tissue (e.g., retinoblastoma, nephroblastoma).

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3. Characteristics of Benign vs. Malignant Tumors

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4. Anaplasia

• Pleomorphism: Variation in cell size and shape
• Abnormal nuclear morphology: Hyperchromatic nuclei, coarse chromatin, prominent nucleoli
• Increased N:C ratio (may approach 1:1; normal is 1:4 to 1:6)
• Atypical mitoses: Tripolar, quadripolar spindles
• Tumor giant cells: Large, bizarre cells with single/multiple nuclei
• Loss of polarity: Loss of normal orientation of cells

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5. Grading and Staging

Grading

• Grade I: Well differentiated
• Grade II: Moderately differentiated
• Grade III: Poorly differentiated
• Grade IV: Undifferentiated/anaplastic

Staging (more clinically important)

• T (Tumor): Size/local extent (T1-T4)
• N (Nodes): Regional lymph node involvement (N0-N3)
• M (Metastasis): Distant spread (M0, M1)

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6. Tumor Growth and Kinetics

• Doubling time: Time for a tumor to double in size
• Clinical detection threshold: ~10^9 cells (1 gram, ~1 cm)
• Death usually occurs at ~10^12 cells (1 kg)
• Growth fraction: Proportion of cells in replicating pool
• Cell loss: Via apoptosis, exfoliation, differentiation
• Gompertzian growth: Exponential initially, then plateau as tumor enlarges

Tumor Stem Cells

• Small subpopulation with self-renewal and differentiating capacity
• Drive tumor repopulation after therapy
• Identified in leukemias (CD34+/CD38-), breast cancers, brain tumors

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7. Tumor Invasion and Metastasis

1. Lymphatic spread: More common for carcinomas; follows lymphatic drainage
2. Hematogenous spread: More common for sarcomas; via veins (thin-walled)

Cascade of Metastasis (Steps):

1. Detachment: Loss of E-cadherin-mediated cell-cell adhesion
2. Local invasion: Degradation of ECM by proteases (MMPs, cathepsins)
3. Intravasation: Entry into blood/lymph vessels
4. Survival in circulation: Evasion of immune cells, platelet aggregation
5. Arrest and extravasation: At distant site
6. Colonization: Growth in new microenvironment, angiogenesis

Epithelial-Mesenchymal Transition (EMT)

• Tumor cells downregulate E-cadherin, upregulate N-cadherin and vimentin
• Acquire motility and invasive properties
• Key transcription factors: Snail, Slug, Twist, ZEB1/2

Common Sites of Metastasis

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8. Hallmarks of Cancer (Hanahan & Weinberg)

Original 6 Hallmarks (2000):

1. Self-sufficiency in growth signals
2. Insensitivity to anti-growth signals
3. Evasion of apoptosis
4. Limitless replicative potential (telomerase activation)
5. Sustained angiogenesis
6. Tissue invasion and metastasis

Emerging Hallmarks (2011 update):

1. Reprogramming energy metabolism (Warburg effect - aerobic glycolysis)
2. Evading immune destruction

Enabling Characteristics:

• Genomic instability and mutation
• Tumor-promoting inflammation

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9. Molecular Basis of Cancer

Proto-Oncogenes → Oncogenes

• Point mutation: RAS mutations (most common in human cancers)
• Gene amplification: N-MYC (neuroblastoma), HER2/NEU (breast)
• Chromosomal translocation:
  • BCR-ABL: t(9;22) Philadelphia chromosome - CML
  • c-MYC: t(8;14) - Burkitt lymphoma
  • BCL-2: t(14;18) - Follicular lymphoma

Tumor Suppressor Genes (TSG)

p53 Pathway

• Activated by DNA damage, hypoxia, oncogene activation
• Actions: Cell cycle arrest (p21 → CDK inhibition), DNA repair (GADD45), apoptosis (BAX, PUMA)
• Li-Fraumeni syndrome: Germline TP53 mutation → multiple cancers in young patients
• MDM2 is a negative regulator of p53 (forms autoregulatory loop)

RB Pathway

• Active (hypophosphorylated) RB binds E2F transcription factors → inhibits S-phase entry
• CDK4/6-CyclinD phosphorylates RB → releases E2F → cell cycle progression
• p16 (CDKN2A) inhibits CDK4/6 (upstream of RB)
• All cancers bypass G1 checkpoint (via RB loss, CDK overactivation, or p16 inactivation)

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10. Apoptosis in Cancer

Intrinsic Pathway (Mitochondrial)

• Controlled by BCL-2 family proteins
  • Anti-apoptotic: BCL-2, BCL-XL, MCL-1
  • Pro-apoptotic: BAX, BAK, BIM, PUMA, NOXA
• When pro-apoptotic signals > anti-apoptotic: cytochrome C release → apoptosome → caspase-9 → effector caspases

Extrinsic Pathway (Death Receptor)

• FasL/Fas, TNF/TNFR → FADD → caspase-8 → effector caspases

Cancer evasion:

• BCL-2 overexpression: t(14;18) in follicular lymphoma
• FLIP: Inhibitor of caspase-8
• Mutations in FAS, FADD

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11. Telomeres and Telomerase

• Telomeres shorten with each cell division
• After ~60-70 divisions: replicative senescence (M1 checkpoint, p53/RB dependent)
• If p53/RB bypassed: crisis (M2) → chromosomal fusions → genomic instability
• Telomerase (hTERT): Maintains telomere length in stem cells and cancer cells
• 85-90% of cancers express telomerase

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12. Tumor Angiogenesis

• Tumors >1-2 mm require new blood vessels to survive
• Angiogenic switch: Tipping balance toward pro-angiogenic factors
  • Pro-angiogenic: VEGF (key), FGF, PDGF, TGF-β
  • Anti-angiogenic: Thrombospondin-1, angiostatin, endostatin
• VEGF stimulated by: hypoxia (via HIF-1α), oncogene activation, p53 loss
• Tumor vasculature: Leaky, tortuous, arteriovenous shunts

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13. Epigenetics in Cancer

• DNA methylation: CpG island hypermethylation silences TSGs (e.g., RB, VHL, APC)
• Histone modification: Acetylation (active), methylation (active or repressive), deacetylation (inactive)
• Non-coding RNAs:
  • miRNAs: miR-21 (oncomiR, overexpressed in many cancers), let-7 (tumor suppressor, targets RAS)
  • lncRNAs: HOTAIR, MALAT1

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14. Carcinogenesis - Multistep Process

Initiation → Promotion → Progression Model:

1. Initiation: Irreversible mutagenic event (DNA alteration) - rapid, permanent
2. Promotion: Proliferative stimulus; reversible; requires repetition (e.g., chronic irritation, hormones)
3. Progression: Acquisition of malignant phenotype; additional mutations, chromosomal instability

Molecular Sequence (Colon Cancer - Vogelgram):

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15. Chemical Carcinogenesis

Direct-Acting (do not need metabolic activation):

• Alkylating agents (nitrogen mustard, cyclophosphamide)
• Acylating agents

Indirect-Acting (require metabolic activation - CYP450):

Important Chemical Carcinogens and Their Tumors:

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16. Radiation Carcinogenesis

• UV radiation (UVB, 280-320 nm): Pyrimidine dimers → skin cancers (BCC, SCC, melanoma)
• Ionizing radiation (X-ray, gamma, particles): Double-strand DNA breaks, chromosomal aberrations
  • Leukemia (especially AML, CML) - atomic bomb survivors
  • Thyroid carcinoma (post-Chernobyl, childhood head/neck irradiation)
  • Breast cancer (post-radiation therapy)
  • Lung cancer (uranium miners - radon)

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17. Microbial Carcinogenesis

Viral:

HPV Mechanism:

• E6 protein: Binds and degrades p53
• E7 protein: Binds and inactivates RB
• High-risk types: 16, 18, 31, 33

EBV Mechanism:

• Infects B lymphocytes via CD21
• LMP-1: Mimics CD40 (constitutive activation), activates NF-κB
• Burkitt lymphoma: EBV + t(8;14) (c-MYC translocation)

Bacterial:

• H. pylori: Gastric adenocarcinoma, MALToma
  • Chronic inflammation → IL-8, ROS → DNA damage
  • CagA protein: Activates oncogenic signaling

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18. Immune Surveillance and Evasion

Immune Surveillance:

• NK cells: Kill cells lacking MHC class I
• CTLs (CD8+): Kill via perforin/granzyme, FasL
• Tumor-associated macrophages (TAM), NK cells, NKT cells

Tumor Evasion Mechanisms:

1. Downregulation of MHC class I: Escape from CTL killing
2. Expression of FasL: Kill infiltrating lymphocytes
3. Production of immunosuppressive molecules: TGF-β, IL-10, VEGF
4. Regulatory T cells (Tregs) and MDSCs: Suppress immune response
5. PD-L1 expression: Binds PD-1 on T cells → T cell exhaustion (target of checkpoint inhibitors)
6. CTLA-4 pathway: Blocks T cell co-stimulation

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19. Paraneoplastic Syndromes

• Ectopic hormone production
• Immune cross-reactivity (autoimmune)

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20. Tumor Markers

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21. Lab Diagnosis of Cancer

Morphologic Methods:

• Cytology: Pap smear, FNA, sputum cytology
• Histopathology: Core biopsy, excisional biopsy, frozen section
• Special stains: PAS, Alcian blue, reticulin, Masson trichrome

Immunohistochemistry (IHC):

• Cytokeratin (CK): Carcinomas
• Vimentin: Sarcomas, melanoma, lymphoma
• LCA (CD45): Lymphomas
• Desmin: Muscle tumors
• S-100: Neural tumors, melanoma
• CD10: Renal cell carcinoma, ALL
• ER/PR/HER2: Breast cancer (treatment)
• PSA: Prostate

Molecular Techniques:

• FISH: HER2 amplification, BCR-ABL detection
• PCR: BCR-ABL quantification, minimal residual disease
• NGS: Comprehensive mutation profiling
• Flow cytometry: Immunophenotyping in leukemia/lymphoma
• Cytogenetics: Karyotyping, chromosomal translocations

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22. Key Genetic Syndromes Predisposing to Cancer

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23. DNA Repair and Cancer

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High-Yield Summary Points

1. Most common oncogene mutated in human cancers: RAS (point mutation, ~30%)
2. Most common TSG mutated in human cancers: TP53 (>50%)
3. Hallmark of malignancy: Metastasis
4. Two-hit hypothesis: Knudson; applies to all TSGs; first hit = mutation, second hit = LOH
5. Philadelphia chromosome: t(9;22) → BCR-ABL → CML (also some ALL)
6. E6/E7 of HPV: Degrade p53/RB respectively
7. BCL-2 overexpression: t(14;18) → anti-apoptotic → Follicular lymphoma
8. Warburg effect: Aerobic glycolysis even in presence of O2; cancer cells prefer glycolysis for anabolic building blocks
9. Telomerase: Expressed in >85% cancers; maintains telomeres; allows unlimited replication
10. Paraneoplastic hypercalcemia: PTHrP from squamous cell lung cancer
11. SIADH + Cushing from ectopic hormones: Small cell lung cancer
12. AFP elevated: HCC + yolk sac tumor
13. Vinyl chloride: Angiosarcoma of liver (not hepatocellular)
14. Asbestos alone: Mesothelioma; Asbestos + Smoking = synergistic for lung carcinoma

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Neoplasia - UHS Style MCQs

Robbins Pathology

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• A) Adenocarcinoma
• B) Fibrosarcoma
• C) Fibroadenoma ✓
• D) Phyllodes tumor
• E) Intraductal papilloma

Explanation: Well-encapsulated, no invasion, no atypical mitoses = benign tumor. Breast fibroadenoma is the most common benign breast tumor in young women. Adenocarcinoma would show invasion and nuclear atypia.

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• A) Dysplasia
• B) Metaplasia
• C) Hyperplasia
• D) Anaplasia ✓
• E) Carcinoma in situ

Explanation: Anaplasia features = pleomorphism, hyperchromatic nuclei, increased N:C ratio, atypical (tripolar/quadripolar) mitoses, and tumor giant cells. This is a hallmark of poorly differentiated malignant tumors.

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• A) Philadelphia chromosome
• B) Oncogene activation
• C) Knudson's two-hit hypothesis ✓
• D) Warburg effect
• E) EMT

Explanation: Retinoblastoma is the classic example of Knudson's two-hit hypothesis. Both alleles of RB1 (13q14) must be lost. In hereditary form: 1st hit = germline, 2nd hit = somatic. In sporadic form: both hits are somatic.

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• A) t(8;14)
• B) t(14;18)
• C) t(15;17)
• D) t(9;22) ✓
• E) t(11;22)

Explanation: t(9;22) = Philadelphia chromosome → BCR-ABL fusion gene → constitutively active tyrosine kinase → CML. t(8;14) = Burkitt lymphoma (c-MYC). t(14;18) = Follicular lymphoma (BCL-2). t(15;17) = AML-M3 (PML-RARA).

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• A) Squamous cell carcinoma of lung
• B) Large cell carcinoma
• C) Carcinoid tumor
• D) Small cell carcinoma of lung ✓
• E) Adenocarcinoma of lung

Explanation: Small cell carcinoma (neuroendocrine origin) is the classic cause of ectopic ACTH → Cushing syndrome, and ectopic ADH → SIADH. Squamous cell carcinoma causes hypercalcemia via PTHrP.

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• A) Bony metastases releasing calcium
• B) Ectopic calcitonin production
• C) Vitamin D overproduction
• D) PTHrP (parathyroid hormone-related protein) secretion ✓
• E) Ectopic PTH production

Explanation: Squamous cell carcinoma of lung is the most common cause of humoral hypercalcemia of malignancy via PTHrP. PTHrP mimics PTH action but is not detected by PTH assay, so PTH is suppressed. This is a paraneoplastic syndrome.

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• A) Activating caspase cascade
• B) Increasing cell cycle progression
• C) Activating RAS signaling
• D) Inhibiting apoptosis ✓
• E) Promoting angiogenesis

Explanation: BCL-2 is an anti-apoptotic protein located on the outer mitochondrial membrane. Its overexpression prevents cytochrome C release, blocking the intrinsic apoptotic pathway. Cancer cells accumulate because they cannot die, not because they divide faster.

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• A) Hepatocellular carcinoma
• B) Cholangiocarcinoma
• C) Hepatic adenoma
• D) Angiosarcoma of the liver ✓
• E) Hemangioendothelioma

Explanation: Vinyl chloride → angiosarcoma (hemangiosarcoma) of the liver. This is a classic UHS association. Aflatoxin B1 and HBV/HCV → hepatocellular carcinoma. Arsenic also causes angiosarcoma of the liver.

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• A) 25%
• B) 50%
• C) 75%
• D) 100% ✓
• E) 30%

Explanation: Familial Adenomatous Polyposis (FAP) caused by germline APC mutation (5q21) leads to hundreds to thousands of colonic polyps. Without prophylactic colectomy, 100% of patients develop colorectal carcinoma by age 40-50.

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• A) CEA
• B) CA-125
• C) PSA
• D) AFP (Alpha-fetoprotein) ✓
• E) CA 19-9

Explanation: AFP is elevated in hepatocellular carcinoma and yolk sac tumors. It is used for monitoring response to treatment and detecting recurrence. CEA = colon cancer. CA-125 = ovarian cancer. PSA = prostate cancer. CA 19-9 = pancreatic cancer.

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• A) Integration into RAS proto-oncogene
• B) Activation of BCL-2
• C) E6 degrades p53; E7 inactivates RB ✓
• D) E6 activates telomerase; E7 activates MYC
• E) Chronic inflammation causing microsatellite instability

Explanation: High-risk HPV (16, 18) encodes E6 and E7 oncoproteins. E6 binds and targets p53 for ubiquitin-mediated degradation. E7 binds and inactivates RB, releasing E2F → unchecked S-phase entry. Both tumor suppressor pathways are simultaneously disabled.

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• A) Cyclin-dependent kinase activator
• B) Transcription factor
• C) RAS-GTPase activating protein (GAP) ✓
• D) Receptor tyrosine kinase
• E) Anti-apoptotic protein

Explanation: Neurofibromin (NF1 gene product) is a RAS-GAP - it accelerates GTP hydrolysis on RAS, converting active RAS-GTP to inactive RAS-GDP. When NF1 is mutated/lost, RAS remains constitutively active → uncontrolled proliferation. This is a classic TSG acting as an indirect RAS regulator.

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• A) Osteolytic metastasis
• B) Mixed metastasis
• C) Osteoblastic metastasis ✓
• D) Pathological fracture
• E) Paget disease

Explanation: Prostate cancer classically causes osteoblastic (sclerotic/dense) bone metastases - increased bone density on X-ray. Most other cancers (breast, lung, kidney, thyroid, myeloma) cause osteolytic (punched-out) lesions. Mnemonic: "Prostate = bone-forming" (osteoBLAStic).

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• A) Increased oxidative phosphorylation in hypoxic conditions
• B) Decreased glucose uptake in rapidly dividing cells
• C) Aerobic glycolysis - preferential use of glycolysis even in presence of oxygen ✓
• D) Fatty acid oxidation as the primary energy source
• E) Mitochondrial overactivity in tumor cells

Explanation: The Warburg effect = aerobic glycolysis - cancer cells convert glucose to lactate even when oxygen is abundant. This is inefficient for ATP but provides carbon skeletons, NADPH, and ribose-5-phosphate for biosynthesis (anabolic precursors) needed for rapid growth. Basis of FDG-PET scanning.

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• A) TP53
• B) APC
• C) RB1
• D) BRCA1 or BRCA2 ✓
• E) MLH1

Explanation: BRCA1 (17q) and BRCA2 (13q) are TSGs involved in homologous recombination DNA repair. Germline mutations predispose to breast cancer (lifetime risk 50-85%) and ovarian cancer (15-45%). Young age at diagnosis, bilateral breast cancer, and family history are hallmarks of hereditary BRCA-related cancer.

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• A) Burkitt lymphoma
• B) Nasopharyngeal carcinoma
• C) Hodgkin lymphoma
• D) Adult T-cell leukemia ✓
• E) Post-transplant lymphoproliferative disorder

Explanation: Adult T-cell leukemia/lymphoma is caused by HTLV-1 (Human T-lymphotropic virus type 1), not EBV. EBV is associated with Burkitt lymphoma (especially African endemic type), nasopharyngeal carcinoma, Hodgkin lymphoma (mixed cellularity type), and post-transplant lymphoproliferative disorder.

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• A) Loss of heterozygosity at 17p
• B) Gene amplification of HER2
• C) t(9;22) translocation
• D) Microsatellite instability (MSI-H) ✓
• E) CpG island hypomethylation

Explanation: Mismatch repair (MMR) deficiency leads to accumulation of errors at microsatellite sequences (short tandem repeats) → microsatellite instability (MSI-H). Lynch syndrome is caused by germline mutations in MLH1, MSH2, MSH6, PMS2. MSI-H tumors respond well to PD-1 checkpoint inhibitors (pembrolizumab).

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• A) Hepatocellular carcinoma
• B) Wilms tumor
• C) Neuroblastoma
• D) Hepatoblastoma ✓
• E) Yolk sac tumor

Explanation: Hepatoblastoma is the most common primary liver malignancy in children (<5 years). It shows elevated AFP, fetal/embryonal histology, and arises from hepatic progenitor cells. APC/β-catenin mutations are common. HCC is rare in children (associated with chronic HBV).

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• A) Nitrogen mustard
• B) Cyclophosphamide (as administered)
• C) Benzo[a]pyrene ✓
• D) Bis-chloromethyl ether
• E) β-propiolactone

Explanation: Benzo[a]pyrene (in cigarette smoke/grilled meat) is a procarcinogen that requires CYP450 (especially CYP1A1) to be converted to its active carcinogenic epoxide form (benzo[a]pyrene-7,8-diol-9,10-epoxide). Direct-acting carcinogens (nitrogen mustard, β-propiolactone) do not require metabolic activation.

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• A) Myasthenia gravis
• B) Subacute cerebellar degeneration
• C) Lambert-Eaton myasthenic syndrome ✓
• D) Dermatomyositis
• E) Guillain-Barre syndrome

Explanation: Lambert-Eaton syndrome = paraneoplastic syndrome in small cell lung cancer. Antibodies against voltage-gated calcium channels (VGCC) at presynaptic nerve terminals impair ACh release. Key distinction from MG: Lambert-Eaton IMPROVES with repetitive stimulation (facilitation); MG WORSENS.

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• A) Clonal evolution
• B) Tumor dormancy
• C) Angiogenic switch
• D) Epithelial-Mesenchymal Transition (EMT) ✓
• E) Anoikis resistance

Explanation: EMT is a process where epithelial cells lose cell-cell adhesion (E-cadherin loss) and gain mesenchymal properties (vimentin, N-cadherin, fibronectin). Key transcription factors: Snail, Slug, Twist, ZEB1/2. This enables invasion and intravasation - critical early steps in metastasis cascade.

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• A) Thyroglobulin
• B) TSH
• C) AFP
• D) Calcitonin ✓
• E) CA-125

Explanation: Medullary thyroid carcinoma arises from parafollicular C-cells which produce calcitonin. Calcitonin is used as both a diagnostic marker and for monitoring recurrence/metastasis. It is also used for screening family members in MEN2 (where RET proto-oncogene is mutated).

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• A) MEN1 gene - pheochromocytoma
• B) VHL gene - adrenal medulla tumor
• C) NF1 gene - medullary thyroid cancer
• D) RET proto-oncogene - medullary thyroid carcinoma and pheochromocytoma ✓
• E) APC gene - colorectal cancer

Explanation: MEN2 is caused by germline activating mutations in the RET proto-oncogene (not a TSG, but an oncogene). RET encodes a receptor tyrosine kinase. MEN2A: medullary thyroid carcinoma + pheochromocytoma + hyperparathyroidism. MEN2B adds marfanoid habitus and mucosal neuromas. Important: RET is a proto-oncogene, not a TSG - gain-of-function mutation.

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• A) Lymphoma
• B) Melanoma
• C) Sarcoma
• D) Carcinoma ✓
• E) Glioma

Explanation: IHC markers: CK+ = carcinoma (epithelial origin). LCA/CD45+ = lymphoma. S-100+ = melanoma, neural tumors, Langerhans cells. Vimentin+ = sarcoma, melanoma, lymphoma. Desmin+ = muscle tumors. GFAP+ = glioma. Positivity for CK alone points strongly to carcinoma.

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• A) RAS mutation
• B) TP53 loss
• C) SMAD4 loss
• D) APC loss ✓
• E) MLH1 silencing

Explanation: The Vogelgram for colorectal cancer: APC loss (first hit, initiating) → hyperproliferative epithelium → KRAS mutation → early adenoma → SMAD2/4 loss (TGF-β pathway) → late adenoma → TP53 loss → invasive carcinoma → further alterations → metastasis. APC loss is the gate-keeper event (chromosome 5q21).

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Quick Revision - Exam Tips

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Robbins Chapter 3

Hemodynamic Disorders, Thromboembolism, and Shock

Complete Notes

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1. EDEMA

• Transudate: Protein-poor, low specific gravity fluid (<1.012). Due to hydrostatic/osmotic imbalance. (e.g., heart failure, nephrotic syndrome)
• Exudate: Protein-rich, high specific gravity fluid (>1.020). Due to inflammation → increased vascular permeability. (e.g., infection, injury)
• Anasarca: Severe, generalized edema with massive subcutaneous tissue swelling
• Ascites: Fluid in peritoneal cavity
• Hydrothorax: Fluid in pleural cavity
• Hydropericardium: Fluid in pericardial sac

Causes / Mechanisms:

Morphology:

• Subcutaneous edema: "Pitting edema" - finger leaves temporary depression
• Pulmonary edema: Alveoli filled with fluid → dyspnea, cyanosis, frothy pink sputum; heavy, boggy lungs
• Cerebral edema: Life-threatening; herniation risk; after trauma, hypoxia, encephalitis

Clinical significance by location:

• Lower extremity edema: Cosmetic nuisance but can impair wound healing
• Pulmonary edema: Impairs gas exchange → hypoxia → LIFE THREATENING
• Brain edema: Herniation → death
• Periorbital edema: Early sign in nephrotic syndrome (children)

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2. HYPEREMIA AND CONGESTION

Chronic Passive Congestion - Organ Changes:

• Right heart failure → blood backs up into pulmonary veins
• Alveolar capillaries engorged → microhemorrhages → RBCs enter alveoli → macrophages phagocytose Hb → form hemosiderin (golden-brown pigment)
• Heart failure cells = hemosiderin-laden macrophages in alveoli
• Lung appears brown and firm (induration)

• Right heart failure → hepatic vein congestion → centrilobular (zone 3) sinusoidal distension
• Central veins + sinusoids dilated and congested → dark red centers
• Surrounding portal zones (zone 1) relatively spared → yellow-tan fatty change
• Gross appearance: "Nutmeg liver" - dark red center, yellow-tan periphery
• Histology: Centrilobular necrosis (zone 3 most vulnerable - farthest from blood supply)
• Long-standing: Cardiac cirrhosis (fibrosis replaces necrotic areas)

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3. HEMORRHAGE

Types by mechanism:

• Rhexis: Rupture of vessel wall (trauma, atherosclerosis, aneurysm)
• Diapedesis: Leakage through small vessels (increased hydrostatic pressure, vitamin C deficiency)

Types by location/size:

Clinical significance:

• Small hemorrhages in non-critical sites: Inconsequential
• Rapid loss of >20% blood volume → hypovolemic shock
• Slowly accumulated large amounts tolerated (body compensates)
• Hematoma breakdown: Hemoglobin → hemosiderin (iron storage) + bilirubin (jaundice)

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4. HEMOSTASIS AND THROMBOSIS

Normal Hemostasis - Three Steps:

1. Vascular spasm - immediate vasoconstriction (endothelin, neural reflex)
2. Platelet adhesion - von Willebrand Factor (vWF) bridges between exposed subendothelial collagen and platelet GpIb receptor
3. Platelet activation - ADP (from platelets), thromboxane A2 (TxA2), thrombin → platelet activation → shape change → release of granules
   • α-granules: vWF, fibrinogen, fibronectin, platelet factor 4
   • Dense (δ) granules: ADP, ATP, Ca²⁺, serotonin, histamine
4. Platelet aggregation - activated platelet GpIIb/IIIa binds fibrinogen → cross-links platelets → loose primary plug

• Tissue factor (TF/Factor III) exposed at injury site → activates extrinsic pathway
• Coagulation cascade amplified → thrombin generation (the key enzyme)
• Thrombin converts soluble fibrinogen → insoluble fibrin strands
• Factor XIIIa cross-links fibrin → stable clot
• Thrombin's additional roles: Activates platelets, activates factors V, VIII, XI, XIII; endothelial cell activation

• Limits clot to injury site; prevents occlusion of normal vessel

Coagulation Cascade:

EXTRINSIC PATHWAY:          INTRINSIC PATHWAY:
Tissue Factor (TF)          Contact activation
+ Factor VII                Factor XII → XIIa
↓                           ↓ XI → XIa
Factor X activation         ↓ IX → IXa
                            ↓
         COMMON PATHWAY:
         Xa + Va + Ca²⁺ + Phospholipid
         (Prothrombinase complex)
         ↓
         Prothrombin → THROMBIN
         ↓
         Fibrinogen → FIBRIN → Cross-linked Fibrin (via XIIIa)

Anticoagulant Properties of Normal Endothelium:

• Prostacyclin (PGI₂) - vasodilator + inhibits platelet aggregation
• Nitric oxide (NO) - vasodilator + inhibits platelets
• Adenosine diphosphatase - degrades ADP

• Thrombomodulin: Binds thrombin → changes its substrate specificity → activates Protein C
• Protein C/Protein S complex: Degrades Factors Va and VIIIa
• Heparin-like molecules: Activate Antithrombin III → inhibits thrombin, IXa, Xa, XIa, XIIa
• TFPI (Tissue Factor Pathway Inhibitor): Inhibits TF/VIIa complex

• t-PA (tissue Plasminogen Activator): Converts plasminogen → plasmin → lyses fibrin clot

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5. THROMBOSIS

Virchow's Triad - Three Primary Causes:

        THROMBOSIS
       /    |    \
Endothelial  Stasis/   Hypercoagu-
  Injury    Turbulence  lability

• Physical injury (trauma, surgery, catheterization)
• Atherosclerosis (plaque disruption exposes collagen)
• Hypertension
• Bacterial toxins, cytokines
• Cigarette smoke products
• Hypercholesterolemia, homocysteinemia

• Stasis (slow flow) allows platelets to contact endothelium, prevents dilution of activated clotting factors, impedes inhibitor inflow
• Turbulence damages endothelium, creates areas of stasis downstream
• Examples: Atrial fibrillation (stasis in atria), cardiac aneurysm (stasis), DVT (leg veins, immobility), polycythemia, hyperviscosity

• Prolonged bed rest / immobilization
• Pregnancy (↑ clotting factors, venous stasis)
• Oral contraceptives / HRT (↑ estrogen → ↑ coagulation factors, ↓ Protein C/S)
• Malignancy (tumor cells produce procoagulants; Trousseau syndrome)
• Antiphospholipid antibody syndrome (lupus anticoagulant)
• Heparin-induced thrombocytopenia (HIT) - paradoxical!
• Nephrotic syndrome (loss of antithrombin III in urine)

Morphology of Thrombi:

• Mural thrombus: Attached to heart/aorta wall (doesn't occlude completely); LV wall after MI, atrium in A-fib
• Occlusive thrombus: Completely blocks vessel; common in small/medium arteries and veins
• Vegetations: Thrombi on heart valves; in infective endocarditis, non-bacterial thrombotic endocarditis (marantic)

Fate of Thrombi (5 Ds):

1. Dissolution (Lysis): Fibrinolytic system dissolves small/fresh thrombi (t-PA)
2. Propagation: Thrombus grows, accumulates more platelets/fibrin, may occlude
3. Embolization: Fragments break off → embolus
4. Organization and Recanalization: Thrombus invaded by endothelial cells, smooth muscle cells, fibroblasts → becomes organized connective tissue; new channels reform through clot (recanalization) → partial flow restoration
5. Resolution: Complete dissolution and removal

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6. DISSEMINATED INTRAVASCULAR COAGULATION (DIC)

Key Concept: "Consumption coagulopathy"

• Clotting factors and platelets consumed → bleeding despite thrombosis

Causes:

Pathogenesis:

1. Trigger → release of Tissue Factor (TF) or thromboplastic substances
2. Systemic activation of coagulation → fibrin microthrombi everywhere
3. Consumption of platelets, fibrinogen, factors V and VIII
4. Activation of fibrinolytic system → increased D-dimers (fibrin degradation products)
5. Result: Bleeding (thrombocytopenia + factor deficiency) + ischemia (from microthrombi)

Lab findings in DIC:

Clinical features:

• Spontaneous bleeding from multiple sites (IV sites, gums, GI tract, skin petechiae)
• Organ dysfunction from microthrombi (renal cortical necrosis, adrenal hemorrhage [Waterhouse-Friderichsen], pulmonary infarcts)
• Shock

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7. EMBOLISM

Types of Emboli:

A. Pulmonary Thromboembolism (PTE)

• Hemorrhagic, wedge-shaped (base on pleura)
• Red (hemorrhagic) infarction due to dual blood supply
• 60% of emboli → NO infarction (dual blood supply protects)
• Infarction more likely if: pre-existing cardiac/pulmonary compromise

• Sudden onset dyspnea, pleuritic chest pain, hemoptysis
• Massive PTE: Sudden death (obstructive shock), hypoxemia, hypotension, tachycardia
• "Saddle embolus" - large embolus straddling pulmonary artery bifurcation

B. Systemic (Arterial) Thromboembolism

• Source: 80% from intracardiac mural thrombi
  • 2/3 from left ventricle infarcts
  • 25% from dilated left atria (mitral valve disease, A-fib)
  • Others: aortic aneurysms, atherosclerotic plaques, paradoxical emboli
• Sites: Lower extremities (75%), CNS (10%), intestines, kidneys, spleen
• Usually causes infarction (end-arteries with no collateral)

C. Fat Embolism

• Fat globules enter circulation from disrupted marrow sinusoids
• Small emboli: common incidental finding (CPR), usually clinically silent
• Fat embolism syndrome (1-3 days after fracture):

1. Pulmonary insufficiency (respiratory failure, hypoxemia)
2. Neurologic symptoms (confusion, seizures, coma)
3. Petechial rash (classic - on upper body, axillae, conjunctivae)

• Plus: anemia, thrombocytopenia, fever, tachycardia

D. Amniotic Fluid Embolism

• Rare but catastrophic complication of late pregnancy/delivery/postpartum
• Amniotic fluid + fetal material enter maternal circulation via uterine vein tears
• Sudden onset: Dyspnea → cyanosis → hypotensive shock → DIC → seizures
• Histology: Squamous cells, mucin, lanugo hair, vernix in pulmonary vessels
• Mortality: 20-40% (high); one of the leading causes of maternal mortality
• Mechanism: Amniotic fluid activates both complement system and coagulation → DIC

E. Air Embolism

• Decompression sickness ("The Bends"): Rapid ascent from deep sea → dissolved N₂ comes out of solution as bubbles
  • Small bubbles: Joint/muscle pain ("bends"), skin mottling
  • Large bubbles: Stroke-like symptoms, pulmonary edema
  • Treatment: Hyperbaric O₂ chamber
  • Caisson disease: Chronic form - ischemic necrosis of bones (femoral head)
• Iatrogenic: Air entry during IV lines, surgery (especially neurosurgery in sitting position), central line placement

• 100 mL air needed to cause death (obstructs right heart outflow)

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8. INFARCTION

Types:

Factors Influencing Infarct Development:

1. Nature of blood supply:
   • Single (end-artery) supply → infarction more likely (kidney, spleen, heart)
   • Dual blood supply → protected (liver, lung, forearm/leg muscles with dual arteries)
2. Rate of occlusion:
   • Slowly developing → collaterals can form → may prevent infarction
   • Sudden occlusion → infarction
3. Tissue vulnerability to hypoxia:
   • Most sensitive: Neurons (3-5 minutes), myocardial cells (20-30 minutes)
   • Most resistant: Fibrous tissue, skeletal muscle (hours)
4. Blood O₂ content:
   • Anemia, cyanosis, CHF → marginal zone becomes infarcted

Morphology:

• Coagulative necrosis in most organs (except brain → liquefactive necrosis)
• Initial: Ischemic coagulative necrosis, cell outlines preserved (ghost cells)
• 12-24 hours: PMN infiltration begins
• Days 3-7: Macrophages (phagocyte dead cells), granulation tissue begins
• Weeks: Scar formation (fibrous replacement)
• Brain infarct: Liquefactive necrosis → fluid-filled cavity (cyst)
• Lung infarct: Hemorrhagic (red), wedge-shaped, pleural friction rub

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9. SHOCK

Types of Shock:

Pathogenesis of Septic Shock (most complex):

• LPS (lipopolysaccharide) → binds TLR4 (Toll-like receptor) on macrophages, endothelial cells → TNF, IL-1, IL-6 release
• TNF-α and IL-1: Fever, neutrophil activation, ↑ coagulation, ↓ anticoagulants → DIC; vasodilation
• NO (nitric oxide): Vasodilation → ↓ SVR → distributive shock
• PAF (platelet-activating factor): Platelet aggregation + vasoconstriction at some sites + ↑ vascular permeability
• Superantigens (Staph toxic shock): Massive polyclonal T-cell activation → cytokine storm

• Vasodilation → hypotension
• ↑ Vascular permeability → edema, fluid loss
• DIC → consumption coagulopathy + microvascular thrombosis
• Metabolic derangements (lactic acidosis)
• Multi-organ dysfunction syndrome (MODS)

Stages of Shock (All Types):

• Neurohumoral mechanisms maintain perfusion
• ↑ HR (tachycardia), ↑ SVR (peripheral vasoconstriction)
• Activation of renin-angiotensin-aldosterone system (RAAS)
• ADH release → water retention
• Vitals: BP maintained or mildly ↓; signs: cool, clammy skin; oliguria begins
• Reversible with treatment

• Compensatory mechanisms overwhelmed
• Widespread tissue hypoxia → anaerobic glycolysis → lactic acidosis
• Acidosis + hypoxia impair cardiac function → further ↓ CO
• Endothelial injury → increased vascular permeability → more fluid loss → worsening shock
• Vital signs deteriorate: Hypotension, tachycardia, altered consciousness
• May still be reversible with aggressive treatment

• Severe, irreversible cell and tissue injury despite treatment
• Loss of lysosomal membranes → release of digestive enzymes → cell autolysis
• Intestinal barrier breakdown → bacterial translocation → worsens sepsis
• Multi-organ dysfunction syndrome (MODS):
  • Kidney: Acute tubular necrosis (ATN) → oliguria/anuria
  • Lung: ARDS (acute respiratory distress syndrome) - "Shock lung"
  • Liver: Centrilobular necrosis
  • Brain: Hypoxic encephalopathy
  • Adrenals: Hemorrhage (Waterhouse-Friderichsen in meningococcemia)
  • GI: "Stress ulcers" (Curling ulcers in burns, Cushing ulcers in brain injury)
• Death is inevitable despite treatment

Morphological Changes in Shock:

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10. KEY DIFFERENCES - HIGH YIELD COMPARISONS

Hyperemia vs Congestion:

Transudate vs Exudate:

Antemortem vs Postmortem Clot:

Red vs White Infarct:

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HIGH-YIELD SUMMARY POINTS

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