Colorectal cancer is one of the commonest cancers in Australia with a cumulative life time risk of 6%. The average age of diagnosis is 65 years of age and 80% of cases occur in people without identifiable risk factors. Early diagnosis is important as prognosis is directly related to the stage of the disease. Fortunately, colorectal cancer arises from a defined precursor lesion that is detectable on screening tests. The two most commonly used screening tests in Australia are faecal occult blood testing (FOBT) and colonoscopy.
Annual FOBT (3 samples on separate days) has good evidence for decreasing mortality from colorectal carcinoma with a detection rate of approximately 75%. The newer immunochemical tests utlilse antibodies to human haemoglobin so don’t require the previous dietary restrictions.
Colonoscopy is the most accurate procedure for detecting early stage colorectal cancer and adenomatous polyps, with the added ability of biopsy or polypectomy during the examination. For an average risk patient older than 50 years old, if colonoscopy is the chosen screening method, it should be repeated every 5 years. A history of multiple adenomas, large size (>10mm), previous colorectal carcinoma, extensive inflammatory bowel disease or a strong family history of carcinoma, requires more frequent colonoscopy and referral to a gastroenterologist for long term care.