Colorectal cancer (CRC) — cancer of the colon or rectum — is the third most commonly diagnosed cancer and the second leading cause of cancer death worldwide. In the United States alone, approximately 153,000 new cases are diagnosed annually. The critical fact about colorectal cancer is its preventability: when detected at an early, localised stage, the five-year survival rate exceeds 90%. Yet approximately 30% of eligible adults remain unscreened — a gap that screening programmes are urgently working to close.
Why Screening Saves Lives
Most colorectal cancers develop slowly from benign polyps — small growths on the colon's inner lining — over a period of 10–15 years. Screening can detect and remove these polyps before they become malignant, making colorectal cancer one of the few cancers that is genuinely preventable through screening, not merely detectable earlier. The US Preventive Services Task Force recommends beginning screening at age 45 for average-risk adults; those with inflammatory bowel disease, a family history of CRC, or hereditary syndromes (Lynch syndrome, familial adenomatous polyposis) require earlier and more frequent surveillance.
Screening Methods
Colonoscopy is the gold standard — a flexible camera directly examines the entire colon; polyps can be removed during the same procedure. Recommended every 10 years in average-risk adults with normal findings. Faecal immunochemical test (FIT) detects blood in stool — annual testing; positive results require follow-up colonoscopy. Stool DNA test (Cologuard) detects both blood and abnormal DNA from tumour cells — every 1–3 years; higher sensitivity but also higher false-positive rate than FIT alone. CT colonography (virtual colonoscopy) provides detailed imaging of the colon without sedation but requires bowel preparation and cannot remove polyps. The "best" screening test is the one the patient will actually complete.
Symptoms and Risk Factors
Early CRC is usually asymptomatic — reinforcing why screening (not symptom-driven investigation) is the critical detection strategy. Symptoms suggesting established disease include blood in or on the stool, a persistent change in bowel habits (new constipation, diarrhoea, or narrowing of stool), abdominal cramping, unexplained weight loss, or fatigue from occult bleeding-associated anaemia. Risk factors beyond age include family history of CRC or polyps, inflammatory bowel disease (Crohn's disease, ulcerative colitis), obesity, physical inactivity, heavy alcohol consumption, processed and red meat consumption, and smoking.
Frequently Asked Questions
Is colonoscopy preparation really necessary?
Yes — adequate bowel preparation (clearing the colon of stool with laxatives and dietary restriction beforehand) is essential for the endoscopist to see the entire colon lining. Inadequate preparation leads to missed polyps and may necessitate repeat procedures. Split-dose preparations (half the evening before, half the morning of the procedure) are better tolerated and more effective than single-dose regimens.
Does diet affect colorectal cancer risk?
Yes. The World Cancer Research Fund estimates that approximately 47% of colorectal cancers are attributable to modifiable lifestyle factors. Processed meat (bacon, sausages, hot dogs) is classified as Group 1 carcinogenic for CRC; red meat as Group 2A (probably carcinogenic). Conversely, dietary fibre from whole grains, legumes, and vegetables is associated with a dose-dependent reduction in CRC risk.
Sources
- USPSTF. Colorectal Cancer Screening Recommendation. 2021.
- World Cancer Research Fund. CRC evidence summary. 2018.
- American Cancer Society. Colorectal Cancer Facts & Figures 2023–2025.