Colorectal Cancer Epidemiology Quiz

Colorectal Cancer Epidemiology

• Commonality: Fourth most common cancer in the USA, second most common cause of cancer death. Overall incidence declining.
• Age: 90% diagnosed after 50. Highest risk is 50-54 years, with approximately 7x higher risk than 20-24 year olds.
• Race: Higher incidence and mortality in African Americans (especially non-Hispanic Blacks).
• Sex: About 30% higher incidence and 44% higher mortality in men than in women.
• Socioeconomic Status: Lower socioeconomic status associated with higher colorectal cancer risk.
• Prior Polyps: 24% chance of malignancy in untreated polyps over 20 years. Early polypectomy associated with 80-90% lower incidence.
• Prior Colon Cancer: 3% five-year risk of recurrence after resection.
• Inflammatory Bowel Disease (IBD): ~1% of new CRC cases annually. 2-4 times higher risk in IBD patients. Incidence in IBD population decreasing. IBD also linked to inflammatory polyps. Typically diagnosed 15-20 years after IBD onset. Patients with IBD diagnosed before 30 have a higher risk. Colorectal cancer accounts for 10% all-cause mortality in ulcerative colitis (UC) and 15% in Crohn's disease.

Ulcerative Colitis (UC) - Specific Risk

• Duration: Cancer risk increases with disease duration.
  • 2% risk at 10 years.
  • 10% at 20 years.
  • 20% at 30 years.
• Pattern: Pancolitis highest risk pattern.
• Associated Conditions: Higher risk, especially in the right colon if primary sclerosing cholangitis is present.
• Site: Most common cancer sites are sigmoid colon and rectum.
• Mortality: UC-associated CRC accounts for ~10% of all-cause mortality in UC.
• Molecular Differences: UC-associated CRC more frequent CIMP, earlier TP53 mutations, and less MSI and KRAS.

Crohn's Disease - Specific Risk

• Risk Factors: Risk related to location, extent, and duration of the disease.
• Severity: Isolated colon involvement has 7x greater risk. Ileal and colon involvement has 3x greater risk. Isolated ileal involvement lowest risk pattern. Left-sided colitis associated with higher risk than right-sided colitis.
• Mortality: Crohn's disease-associated CRC accounts for ~15% of all-cause mortality.

Other Risk Factors

• Smoking: 12% of CRC associated with smoking. Smoking linked to BRAF mutations, high MSI, and CIMP. 60% increased risk in smokers (vs. non-smokers). 60% increased risk correlates with 29 pack-years of smoking. Left-sided colon cancer more common in male smokers; right-sided in female smokers. Poorer prognosis in active smokers.
• Alcohol: 13% of CRC associated with alcohol use. >24g/day consumption linked to 25% increased risk; >50g/day to 50% increased risk. More common in males (due to mean alcohol consumption).
• Meat Consumption: Red meat and processed meats linked to increased risk. Mechanisms may include alkylating damage and KRAS mutations. 20% increased risk per 50g/day of processed meat; 10% per 100g/day red meat.
• Diabetes Mellitus: ~38% increased risk of colon cancer diagnosis, ~20% increased risk of colon cancer mortality. Possible link to liver/lymph node metastases. Metformin linked to decreased risk and better outcomes.
• Exercise: Sedentary lifestyle associated with 25-50% greater risk. Long-term physical activity linked to decreased colon cancer risk, but not rectal cancer. Lifestyle change after diagnosis linked to 40% reduced death risk. 150-300 minutes of moderate or 75-150 minutes of vigorous activity recommended.
• Metabolic Syndrome: Associated with early onset (<50) of colon cancer, especially linked to obesity. Increased incidence and mortality in both men and women.
• Obesity: Males with obesity have 50% greater risk of colon cancer; 25% greater risk of rectal cancer. Females with obesity have 10% higher risk of colon cancer, no effect on rectal cancer risk. Higher waist-to-hip ratio is an independent risk factor.