Cancer Epidemiology & Prevention

Cancer is now the second leading cause of death globally and a fast-rising non-communicable disease (NCD) burden in India. For NEET PG, this topic is a fertile ground for one-liner questions: leading sites by gender, tobacco-attributable cancers, the Bethesda/CIN classification of Pap smears, screening intervals, and the components of the NPCDCS programme. The emphasis is overwhelmingly on secondary prevention (screening) and descriptive epidemiology (registry data).

Magnitude of the problem & registry sources

India records roughly 14–15 lakh new cancer cases and ~9 lakh deaths annually (GLOBOCAN/National Cancer Registry Programme estimates), with the lifetime risk of developing cancer about 1 in 9. Cancer surveillance in India runs through the National Cancer Registry Programme (NCRP), established in 1981 by the ICMR, now coordinated by the National Centre for Disease Informatics and Research (NCDIR), Bengaluru.

Registries are of two types:

• Population-Based Cancer Registries (PBCR) — denominator is the whole population of a defined geographic area; gives incidence rates. This is the gold standard for measuring cancer burden in a community.
• Hospital-Based Cancer Registries (HBCR) — patients attending a hospital; useful for clinical care and patterns of care but cannot give incidence rates (no defined population denominator).

High-yield: PBCR gives incidence; HBCR cannot give incidence because it has no population denominator. NCRP began in 1981 under ICMR.

The crude incidence rate is rising due to ageing, lifestyle/tobacco, and improved detection. Cancer is expressed using the Age-Adjusted Rate (AAR) per 100,000, which removes the confounding effect of differing age structures and allows valid inter-population comparison.

Leading cancer sites in India (NCRP)

This is the single most examined fact in this topic.

Rank	Males	Females
1	Lung (& oral cavity — high overall)	Breast
2	Mouth / oral cavity	Cervix uteri
3	Oesophagus / Stomach	Ovary
4	Stomach	Oral cavity / Lung

• In males, the dominant theme is tobacco-related cancers — lung, mouth, oesophagus, larynx, stomach. In aggregate, head & neck (oral) cancers form the largest group in Indian men.
• In females, breast cancer has overtaken cervical cancer as the commonest cancer in India (a major epidemiological transition; breast > cervix nationally). In rural areas, cervical cancer may still lead, while breast leads in urban registries.
• Childhood cancers: Leukaemia (ALL) is the commonest, followed by lymphomas and CNS tumours.

High-yield: Commonest cancer in Indian females = Breast (overall), having overtaken cervix. Commonest in males = Lung/Oral (tobacco-related). Commonest childhood malignancy = Acute lymphoblastic leukaemia.

Mnemonic for tobacco-attributable cancers — "LOOK BPC PMS": Lung, Oral, Oesophagus, Kidney, Bladder, Pancreas, Cervix, Pharanx/larynx, Myeloid leukaemia, Stomach. About 40% of all cancers in India are tobacco-related — the largest single avoidable cause.

Risk factors & levels of prevention

Cancer epidemiology classically uses the Doll & Peto estimates of attributable fractions; the two biggest avoidable causes are tobacco (~30%) and diet (~35%).

Level	Aim	Cancer examples
Primary	Remove/reduce exposure to risk factors	Tobacco cessation, HPV vaccine, HBV vaccine, occupational hygiene, dietary modification
Secondary	Early detection — screen & treat pre-clinical disease	Pap smear/VIA, mammography, FOBT/colonoscopy, oral visual exam
Tertiary	Limit disability, rehabilitation, palliation	Reconstructive surgery, pain relief/morphine, hospice

High-yield: Vaccination = primary prevention. HPV vaccine (cervical), Hepatitis B vaccine (hepatocellular carcinoma). Screening = secondary prevention.

Established carcinogen associations frequently tested:

• HPV 16 & 18 → cervical cancer (also anal, oropharyngeal). HPV 16/18 cause ~70% of cervical cancers.
• Hepatitis B & C, aflatoxin (Aspergillus flavus) → hepatocellular carcinoma.
• EBV → nasopharyngeal carcinoma, Burkitt lymphoma.
• H. pylori → gastric carcinoma and MALT lymphoma (a Group 1 carcinogen).
• Schistosoma haematobium → squamous cell bladder cancer.
• Aniline dyes / beta-naphthylamine → bladder (transitional cell) cancer.
• Vinyl chloride → hepatic angiosarcoma; asbestos → mesothelioma & lung; arsenic → skin/lung.

Principles of screening (Wilson & Jungner)

A test is offered to apparently healthy, asymptomatic people to detect disease in the detectable pre-clinical phase (DPCP). Screening is justified only when the lead time is long and early treatment improves outcome.

Criteria (Wilson & Jungner, 1968): disease important & common; recognizable latent/early stage; suitable, acceptable, safe test; facility for diagnosis & treatment available; agreed treatment policy; cost-effective; continuous process.

Watch for these biases that wrongly make screening look beneficial:

• Lead-time bias — survival appears longer only because diagnosis is earlier, without changing date of death.
• Length bias — screening preferentially detects slow-growing, indolent (better-prognosis) tumours.
• Overdiagnosis — detecting cancers that would never have caused harm.

High-yield: Best test characteristic for a screening test = high sensitivity (don't miss cases). A confirmatory/diagnostic test should be highly specific. Sensitivity + specificity are intrinsic to the test; PPV/NPV vary with prevalence.

Cervical cancer screening — Pap smear, Bethesda & CIN

This is the highest-yield sub-topic. Cervical cancer is unique because it has a long detectable pre-clinical phase and a well-defined precursor lesion, making screening extremely effective.

Pap smear (Papanicolaou): exfoliative cytology of the squamocolumnar junction / transformation zone (the site of dysplasia). Conventional smear vs liquid-based cytology (LBC) — LBC reduces unsatisfactory smears and allows reflex HPV testing.

CIN (histology) vs Bethesda (cytology)

Histology (CIN)	Old dysplasia term	Bethesda cytology
CIN 1 (lower 1/3 epithelium)	Mild dysplasia	LSIL
CIN 2 (lower 2/3)	Moderate dysplasia	HSIL
CIN 3 / Carcinoma-in-situ (full thickness)	Severe dysplasia / CIS	HSIL
—	—	ASC-US (atypical squamous cells of undetermined significance)

High-yield: The Bethesda system is for reporting cytology (Pap smear) and uses LSIL/HSIL/ASC-US. The CIN grading is histological (biopsy). CIN 1 = LSIL; CIN 2/3 = HSIL.

Screening pathway: Pap/HPV test (screen) → if abnormal → colposcopy (with acetic acid 3–5%; aceto-white areas) → biopsy (confirms diagnosis) → treat (cryotherapy/LEEP/conization).

Stepwise flow: Asymptomatic woman → Pap smear / HPV DNA (screen) → abnormal → Colposcopy → directed Biopsy (gold standard for diagnosis) → CIN grading → Treatment (cryo/LEEP) → follow-up.

Screening recommendations (Bethesda/USPSTF-type, often asked):

• Begin at age 21 (or 25 in some guidelines); cytology every 3 years (21–29 y).
• Age 30–65 y: cytology + HPV co-testing every 5 years, or HPV alone every 5 years, or cytology alone every 3 years.
• HPV DNA testing is the most sensitive primary screen.

High-yield (resource-poor / India): VIA — Visual Inspection with Acetic acid is the recommended screening method under the national programme — cheap, single-visit "screen-and-treat", no lab needed, done by trained health workers. VILI uses Lugol's iodine.

HPV vaccine (primary prevention): quadrivalent (6,11,16,18), bivalent (16,18), nonavalent. India's indigenous CERVAVAC is quadrivalent. Ideal age 9–14 years (before sexual debut) — a two-dose schedule under 15 years; three doses if older/immunocompromised.

Breast cancer screening — mammography

Mammography is the screening modality of choice for breast cancer; it detects clinically occult lesions (microcalcifications). Reported using BI-RADS (0–6).

Modality	Use
Mammography	Primary screening, age 40/50–74, every 1–2 years
Clinical Breast Examination (CBE)	Practical screen in low-resource India
Breast self-examination (BSE)	Awareness only — NOT shown to reduce mortality
MRI	High-risk (BRCA1/2) supplemental screening

High-yield: Screening modality for breast cancer = Mammography. BSE has no proven mortality benefit and is no longer recommended as a screening test — a favourite distractor. In India, CBE is the feasible population strategy.

USPSTF: biennial mammography 40–74 years (recently lowered start to 40). BRCA1/2 mutations → high risk → consider MRI + earlier surveillance ± risk-reducing mastectomy.

Colorectal cancer screening — FOBT

Colorectal cancer screening targets the adenoma → carcinoma sequence, so removing polyps prevents cancer.

Test	Interval	Note
gFOBT / FIT (faecal occult blood)	Annually	Non-invasive, first-line population screen
Flexible sigmoidoscopy	Every 5 years
Colonoscopy	Every 10 years	Gold standard; both screens & removes polyps
FIT-DNA (Cologuard)	Every 1–3 years

High-yield: Begin colorectal screening at age 45 (recently lowered from 50). FOBT annually; colonoscopy every 10 years and is the gold-standard. Annual FOBT positive → colonoscopy.

Oral & other cancers

• Oral cancer: screen by visual inspection of the oral cavity by a trained worker — cheap, high-yield in India given tobacco use. Premalignant lesions: leukoplakia, erythroplakia (highest malignant potential), oral submucous fibrosis (linked to areca/betel nut).
• Stomach: mass endoscopic screening only cost-effective in high-incidence countries (Japan).
• Hepatocellular carcinoma: surveillance with USG + AFP every 6 months in cirrhotics/chronic HBV.
• Lung: Low-dose CT in heavy smokers (55–80 y, 30 pack-years) — chest X-ray and sputum cytology are not effective screens.

NPCDCS / NP-NCD programme

The relevant national programme is the National Programme for Prevention and Control of Cancer, Diabetes, Cardiovascular diseases and Stroke (NPCDCS), launched in 2010, now folded into the broader National Programme for Non-Communicable Diseases (NP-NCD) and delivered through Ayushman Bharat Health & Wellness Centres (HWCs).

Key components:

• Population-Based Screening (PBS) of all adults ≥ 30 years for 5 conditions: hypertension, diabetes, and 3 common cancers — oral, breast, and cervical.
• Screening tools: oral visual examination, clinical breast examination (CBE), and VIA for cervix.
• Three-tier infrastructure: NCD clinics at CHC/District Hospital level; Tertiary Cancer Centres (TCC) and State Cancer Institutes (SCI) for treatment.
• Uses CBAC (Community Based Assessment Checklist) by ASHA/ANM for risk stratification.

High-yield: Under NPCDCS, population screening starts at age 30 and covers oral, breast, and cervical cancers using oral visual exam, CBE, and VIA respectively. This is a classic single-best-answer question.

Other relevant schemes: National Cancer Control Programme (NCCP, 1975/1984–85) — the original programme emphasising tobacco control and pain relief; Tertiary Care Cancer Centre scheme; and the HBCR/NCRP for surveillance. Tobacco control is legally backed by COTPA 2003 and India is a party to the WHO FCTC.

Complications & burden of late presentation

The majority of Indian cancers present in stage III/IV, reflecting poor awareness, lack of screening uptake, and access barriers. Consequences: lower 5-year survival, higher treatment cost, greater need for palliation. Palliative care and morphine availability (tertiary prevention) remain inadequate — a recognised public-health gap and the rationale for the WHO analgesic ladder and the NCCP's pain-relief emphasis.

Key differentials / commonly confused pairs

• CIN vs Bethesda — histology vs cytology (most confused).
• PBCR vs HBCR — incidence vs no incidence.
• Sensitivity vs PPV — intrinsic vs prevalence-dependent.
• Primary vs secondary prevention — vaccine (primary) vs screening (secondary).
• VIA vs VILI — acetic acid vs Lugol's iodine.
• Incidence vs prevalence — for rapidly fatal cancers (e.g., pancreas), incidence ≈ prevalence; for slow cancers, prevalence accumulates.

Recently asked / exam angle

• "Commonest cancer in Indian women" → Breast (overtaken cervix nationally; cervix still leads in some rural registries).
• "Bethesda system is used for" → Cervical cytology reporting (Pap smear).
• "CIN 2 corresponds to" → HSIL / moderate dysplasia.
• "Screening test for cervical cancer in a primary health centre (low resource)" → VIA (acetic acid).
• "BSE / breast self-examination reduces mortality?" → No (distractor; favourite trap).
• "Screening method for colorectal cancer" → FOBT (annual) / colonoscopy (gold standard).
• "NPCDCS screens for which cancers at age 30" → Oral, breast, cervical.
• "Type of registry giving incidence" → Population-based cancer registry (PBCR).
• "Vaccine that prevents cancer" → HPV (cervical), Hepatitis B (liver).
• "Best characteristic of a screening test" → High sensitivity.
• "Lead-time bias" → apparent ↑ survival from earlier diagnosis without delaying death.

Rapid revision

1. NCRP started 1981 under ICMR, coordinated by NCDIR Bengaluru.
2. PBCR → incidence; HBCR → no incidence (no denominator).
3. Commonest cancer: Indian females = Breast; males = Lung/Oral (tobacco); childhood = ALL.
4. ~40% of Indian cancers are tobacco-attributable — the largest avoidable cause.
5. Bethesda = cytology (LSIL/HSIL/ASC-US); CIN = histology. CIN 1 = LSIL; CIN 2/3 = HSIL.
6. Pap smear samples the transformation zone (SCJ); biopsy after colposcopy = gold standard.
7. VIA (acetic acid) is the national low-resource cervical screen; VILI uses Lugol's iodine.
8. HPV vaccine at 9–14 y, 2 doses; CERVAVAC is India's quadrivalent vaccine.
9. Mammography screens breast (40–74 y); BSE has NO mortality benefit; CBE used in India.
10. Colorectal: start age 45, FOBT annually, colonoscopy every 10 years (gold standard).
11. NPCDCS (2010): screens ≥30 y for HTN, DM, and oral, breast, cervical cancers.
12. Screening = high sensitivity; vaccine = primary prevention; screening = secondary prevention.