Cancer & Environmental

Cancer Biochemistry & Environmental Factors

Cancer is a group of diseases characterized by uncontrolled cell proliferation, invasion, and metastasis. It results from accumulated genetic and epigenetic alterations in cell growth control genes.

Molecular Basis of Cancer

  • Proto-oncogenes → Oncogenes: Normal genes promoting growth become overactive. Activation by: point mutation (Ras), amplification (HER2/neu, MYCN), translocation (BCR-ABL in CML, c-Myc in Burkitt lymphoma). Oncogenes are gain-of-function (one mutant allele sufficient).
  • Tumor Suppressor Genes (TSGs)→ loss of growth restriction: Both alleles must be lost (Knudson's Two-Hit Hypothesis). Examples: p53 (mutated in 50% of all cancers; "guardian of the genome"), Rb (retinoblastoma), APC (colon cancer), BRCA1/2, VHL, NF1/2, PTEN.
  • DNA repair gene mutations: MLH1, MSH2 (Lynch syndrome), BRCA1/2 (breast/ovarian). Allow accumulation of further mutations.
  • Apoptosis evasion: BCL-2 overexpression (t(14;18) in follicular lymphoma) blocks apoptosis.
  • Telomere maintenance: Telomerase reactivated in ~85% of cancers → allows unlimited proliferation.

Hallmarks of Cancer (Hanahan & Weinberg)

  1. Sustaining proliferative signaling (growth factors, receptor mutations)
  2. Evading growth suppressors (loss of Rb, p53)
  3. Resisting cell death (BCL-2 overexpression)
  4. Enabling replicative immortality (telomerase)
  5. Inducing angiogenesis (VEGF overexpression)
  6. Activating invasion and metastasis (MMPs, EMT)
  7. Reprogramming energy metabolism (Warburg effect)
  8. Evading immune destruction

Warburg Effect (Aerobic Glycolysis)

Cancer cells preferentially use glycolysis even in the presence of O₂ (aerobic glycolysis). Produces 2 ATP per glucose vs 30–32 ATP (OXPHOS) — apparently inefficient but: ① Faster rate; ② Provides biosynthetic precursors (ribose-5-P for nucleotides, NADPH, amino acid precursors); ③ Creates acidic tumor microenvironment inhibiting immune cells. Basis of PET scan: ¹⁸F-FDG (glucose analog) taken up by metabolically active tumor cells → detected.

Carcinogens

  • Chemical: PAHs (tobacco smoke, charred meat), Aflatoxin B1 (p53 mutation, hepatocellular carcinoma), Nitrosamines, Vinyl chloride (angiosarcoma), Benzene (leukemia), Asbestos (mesothelioma, lung), Arsenic (skin, bladder)
  • Radiation: UV (pyrimidine dimers → NER defect → skin cancer), X-rays/γ-rays (DSBs → leukemia, thyroid), Radon (lung cancer)
  • Viral: HPV 16/18 (E6/E7 inactivate p53/Rb → cervical, head/neck cancer), HBV/HCV (HCC), EBV (Burkitt lymphoma, NPC), HTLV-1 (T-cell leukemia), Helicobacter pylori (gastric MALT lymphoma, adenocarcinoma)

Tumor Markers (Biochemistry)

  • PSA (Prostate-specific antigen): Prostate cancer screening
  • AFP (α-fetoprotein): HCC, testicular germ cell tumors
  • β-hCG: Choriocarcinoma, gestational trophoblastic disease
  • CEA (Carcinoembryonic antigen): Colon, pancreas cancer (monitoring recurrence)
  • CA-125: Ovarian cancer
  • LDH: Lymphoma, testicular cancer
  • Calcitonin: Medullary thyroid carcinoma

Quiz - Exam Preparation Strategy

When studying Quiz for your final board exams, it is critical to focus on the core concepts and fundamental formulas. Relying strictly on NCERT textbook solutions and practicing previous year questions (PYQs) is the proven methodology for scoring high marks. Avoid rote memorization and instead focus on the logical application of the theories presented in this chapter.

⚠️ Common Mistakes to Avoid

❓ Frequently Asked Questions

How can I quickly memorize the concepts of Quiz?

The most effective way is to create short, handwritten revision notes and continuously test your knowledge using our interactive Mock Tests. Spaced repetition and active recall are much better than passive reading.

What type of questions are most commonly asked from Quiz?

Board exams tend to favor conceptual application questions and direct formula-based derivations from the NCERT syllabus. Ensure you have solved every single exercise in the official textbook.

Is reading the NCERT book enough for this chapter?

Yes, the NCERT textbook is the absolute gold standard for board exams. However, to improve your speed and accuracy during the actual exam, you must supplement your reading by solving timed mock tests and objective questions.