Colorectal

# Colorectal Cancer: Rising Threat in Young Adults

## Introduction: The Changing Epidemiology
Colorectal cancer (CRC) presents a disturbing trend: incidence in adults under 50 has increased by 2% annually since 1990. This malignancy develops through a **stepwise adenoma-carcinoma sequence** over 10-15 years, providing a crucial window for prevention. The lifetime risk is 4.3% for men and 4.0% for women, with significant geographic variation (highest in developed nations). Screening advancements have reduced mortality by 55% in screened populations.

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## Causes and Risk Factors: Diet, Genes and Microbiome

### Modifiable Risks
- **Dietary Factors**: Processed meats (IARC Group 1 carcinogen), low fiber intake
- **Obesity**: BMI >30 increases risk 1.3×
- **Vitamin D Deficiency**: <20ng/ml serum level
- **Microbiome Dysbiosis**: Fusobacterium nucleatum association

### Non-Modifiable Risks
- **Inherited Syndromes**: Lynch syndrome (60-80% lifetime risk), FAP
- **Inflammatory Bowel Disease**: UC patients have 2.4× risk after 20 years

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## Prevention Strategies: Screening and Beyond

### Evidence-Based Approaches
- **Screening Modalities**:
  - Colonoscopy (gold standard): Every 10 years from age 45
  - FIT-DNA test (Cologuard): 92% sensitivity for cancer
  - CT Colonography: Alternative for incomplete colonoscopy

- **Chemoprevention**:
  - Aspirin: 40% reduction in Lynch syndrome carriers
  - Metformin: 31% risk reduction in diabetics

### Surgical Prevention
- Prophylactic colectomy for FAP patients