Screening for colorectal cancer
Globally, colorectal cancer (CRC) is the fourth most common cancer in men and the third most common in women, accounting for approximately one million new cases per year The five year survival rate for early stage CRC is greater than 90%, whereas the five year survival rate for those diagnosed with widespread cancer is less than 10%. The natural history of CRC provides an important window of opportunity to diagnose CRC at an early [even pre-malignant] stage. Screening for CRC is an effective method of reducing incidence and mortality rates.
Types of screening
Faecal occult blood testing.
A randomised controlled trial of population screening by faecal occult blood testing in Nottingham has demonstrated a 15% reduction in mortality.
Faecal DNA testing
Clinical accuracy data on faecal DNA tests is still too limited to support population screening.
The UK Flexible Sigmoidoscopy Screening Trial offered screening by a single flexible sigmoidoscopy to patients aged 55 to 64 years. The study, which was reported in The Lancet in 2010 showed that the incidence of colorectal cancer in people attending screening was reduced by 33% and mortality by 43%.
While colonoscopy remains the most accurate screening test for CRC at a single application, it is recognised that colonoscopy misses polyps (an abnormal growth of tissue) and may also miss CRC. Colonoscopy also presents a higher risk of complications than other tests. Serious harm from colonoscopy appears to be about ten times more common with colonoscopy (estimate 3.1 per 1000 procedures) than with flexible sigmoidoscopy (estimate 3.4 per 10,000 procedures).
CT virtual colonoscopy [CTVC]
Published reports on CT virtual colonoscopy (CTVC) screening suggest at least comparable sensitivity to colonoscopy for CRC and large adenomas (benign tumor - 10 mm or larger). CTVC also allows screening for other intra-abdominal abnormalities, but at the expense of a radiation dose.
The NHS Bowel Cancer Screening Programme offers screening every two years to all men and women aged 60 to 69 by faecal occult blood testing. Around 2 in 100 people will receive an abnormal result. They will be referred for further investigation and usually offered a colonoscopy.
For a population of patients >50 years undergoing screening colonoscopy 5-6% can be expected to be found to have cancer or an advanced colonic polyp (an abnormal growth of tissue).