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Botany 3% exam weight

Nutritional Diseases

Part of the INI CET (AIIMS PG) study roadmap. Botany topic pathol-010 of Botany.

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Neoplasia: Carcinogenesis and Tumor Biology covers carcinogenesis and tumor biology for INI CET (AIIMS PG).

Carcinogenesis: Multi-step process from normal cell to malignant tumor.

Hallmarks of Cancer (Hanahan & Weinberg):

  1. Self-sufficiency in growth signals — cancer cells produce their own growth signals (autocrine signaling)
  2. Insensitivity to growth inhibitory signals — loss of tumor suppressors (RB, p53)
  3. Evasion of apoptosis — loss of p53, Bcl-2 overexpression
  4. Limitless replicative potential — telomerase activation
  5. Sustained angiogenesis — VEGF, FGF secretion
  6. Invasion and metastasis — EMT (epithelial-mesenchymal transition), loss of E-cadherin
  7. Reprogramming energy metabolism — Warburg effect (aerobic glycolysis)
  8. Evading immune destruction — PD-L1 expression

Carcinogenic Agents:

  • Chemical carcinogens:
    • Direct acting (no metabolic activation): Alkylating agents, chemotherapeutic drugs (cyclophosphamide)
    • Indirect acting (require metabolic activation): Polycyclic aromatic hydrocarbons (benzo[a]pyrene — tobacco smoke), aflatoxin B1 (liver cancer), nitrosamines
    • Initiation + Promotion: Initiation (irreversible mutation) → Promotion (clonal expansion)
  • Radiation: UV light (skin cancer, melanoma), ionizing radiation (leukemia, solid tumors)
  • Viral oncogenesis:
    • HPV → cervical cancer, oropharyngeal cancer (E6/E7 proteins inactivate p53/RB)
    • HBV/HCV → hepatocellular carcinoma
    • EBV → Burkitt lymphoma, nasopharyngeal carcinoma
    • HTLV-1 → Adult T-cell leukemia/lymphoma

Oncogenes and Tumor Suppressors:

  • Oncogenes (gain of function): HER2/neu (breast cancer), RAS (many cancers), BCR-ABL (CML — Philadelphia chromosome t(9;22)), MYC (Burkitt lymphoma)
  • Tumor suppressors (loss of function): p53 (most frequently mutated — Li-Fraumeni), RB (retinoblastoma), APC (familial adenomatous polyposis), BRCA1/2 (breast/ovarian cancer)
  • Knudson two-hit hypothesis: Both alleles must be inactivated for tumor suppressor to function (retinoblastoma model)

Tumor Microenvironment (TME):

  • Cancer cells recruit fibroblasts (CAFs — cancer-associated fibroblasts)
  • Immunosuppressive cells (T-regs, MDSCs)
  • Angiogenic factors (VEGF, PDGF)

Metastasis:

  1. Invasion of basement membrane (loss of E-cadherin)
  2. Intravasation (entry into lymphatics or blood vessels)
  3. Survival in circulation (immune evasion — CTCs)
  4. Extravasation at distant site
  5. Colonization (seed and soil hypothesis — some organs more receptive)

⚡ Exam Tip for INI CET (AIIMS PG): p53 = “Guardian of the genome” — most commonly mutated gene in human cancer (~50% of all cancers). BRCA1/2 = DNA repair genes — mutations cause hereditary breast/ovarian cancer.