Cancer Epidemiology and Prevention

Intro to Cancer Epidemiology - Numbers & Trends Game

• Cancer Epidemiology: Study of cancer distribution & determinants in populations.
• Key Metrics:
  • Incidence: New cases/defined pop/time. (Measures risk)
  • Prevalence: Total existing cases (new+old)/pop/point in time. (Measures burden)
  • Mortality Rate: Deaths from cancer/pop/time.
  • Survival Rate: % alive for period (e.g., 5-yr) post-diagnosis.
• Important Rates:
  • Crude Rates: Observed rates in a pop.
  • Age-Standardized Rates (ASR): Age-adjusted for fair comparison across pops.
• Data Source: GLOBOCAN (IARC): Global stats.
• General Trends: ↑ global incidence; improving survival for many.

⭐ Lung cancer: most common diagnosis in males & leading cause of cancer death globally.

Cancer Risk Factors & Etiology - The Usual Suspects

• Chemicals:
  • Tobacco (Polycyclic Aromatic Hydrocarbons, Nitrosamines): Lung, oral, bladder.
  • Aflatoxin $B_1$ (Aspergillus): Hepatocellular carcinoma (HCC).
  • Asbestos: Lung, mesothelioma, laryngeal.
  • Arsenic: Skin (palms/soles), lung, bladder.
  • Benzene: Leukemia.
  • Vinyl chloride: Liver angiosarcoma.
• Radiation:
  • Ionizing (X-rays, radon): Leukemia, thyroid.
  • UV (Sunlight - UVB): Skin (melanoma, BCC, SCC).
• Infections:
  • Viruses: HPV (cervical, anal, oropharyngeal), HBV/HCV (HCC), EBV (Burkitt's, nasopharyngeal), HTLV-1 (ATL), HHV-8 (Kaposi).
  • Bacteria: H. pylori (gastric adenocarcinoma, MALToma).
  • Parasites: Schistosoma haematobium (bladder SCC), Clonorchis sinensis (cholangiocarcinoma).
• Lifestyle/Heredity:
  • Alcohol (synergistic with tobacco).
  • Diet (↑fat/↓fiber, obesity).
  • Genetics (BRCA, Lynch).

⭐ Tobacco smoke is the single most important environmental carcinogen, implicated in ~30% of all cancer deaths in developed countries.

Indian Cancer Scenario - India's Cancer Atlas

• Source: National Centre for Disease Informatics and Research (NCDIR-ICMR).
• Leading Cancers (India): Lung, Breast, Cervical, Oral, Colorectal.
• Common Cancers by Gender:
  • Males: Lung, Oral cavity, Prostate, Stomach, Colorectal.
  • Females: Breast, Cervix uteri, Ovary, Colorectal, Lung.
• Regional Hotspots:
  • Northeast: ↑ Oesophageal, Stomach cancers.
  • Gangetic belt: ↑ Gallbladder cancer (females).
• Notable Trends:
  • ↑ Breast cancer (especially urban).
  • ↑ Colorectal cancer.
  • ↓ Cervical cancer (variable, improved screening).
• High burden of tobacco-related cancers (TRCs).

⭐ Tobacco-related cancers (TRCs) constitute about 30% of the cancer burden in males and 10-12% in females in India.

Cancer Prevention & Screening - Shield & Scope

• Levels of Prevention:
  • Primary: Prevent cancer onset.
    • Lifestyle: Healthy diet, exercise, no tobacco/alcohol.
    • Vaccines: HPV (Cervical, H&N), HBV (Liver).
    • Chemoprevention: Tamoxifen (Breast), Aspirin (CRC).
  • Secondary (Screening): Early detection.
    • Cervical: Pap smear (Age 30-65 yrs, q3-5 yrs); VIA/VILI.
    • Breast: SBE, CBE, Mammography (Age >50 yrs, or >40 high-risk).
    • Oral: OVE (tobacco users).
    • Colorectal: FOBT/Colonoscopy (Age >50 yrs).
  • Tertiary: Limit complications post-diagnosis (rehab, palliative).

⭐ Screening is justified if benefits (early detection, improved outcomes) outweigh harms (overdiagnosis, cost, anxiety) - core of Wilson-Jungner criteria.

High‑Yield Points - ⚡ Biggest Takeaways

• Tobacco is the leading preventable cause of cancer mortality in India.
• Key oncogenic infections: HPV (cervical), HBV/HCV (liver), H. pylori (stomach).
• Early detection via screening for cervical, breast, and oral cancers is vital.
• Lifestyle modifications: ↑fruits/vegetables, regular exercise, ↓alcohol significantly reduce risk.
• Occupational carcinogens like asbestos (mesothelioma) and benzene (leukemia) are important.
• Common cancers in India: Men - Lung/Oral; Women - Breast/Cervical.