COLORECTAL CANCER SCREENING
Colorectal Cancer Screening
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
In the UK there are currently two types of screening for colorectal cancer: faecal occult blood testing followed by colonoscopy, or flexible sigmoidoscopy. There are, additionally, other alternatives that have been studied.
Faecal occult blood testing
Faecal occult blood testing has been shown in a randomized controlled trial to result in a 15% reduction in mortality from colorectal cancer. When a positive test is obtained as part of screening it is recommended that the patient undergo a colonoscopy to examine the colon.
Colonoscopy remains the most accurate test for CRC. However, it is recognised that polyps (abnormal growths of tissue) can be missed, as may cancers occasionally. Colonoscopy is also associated with a higher risk of complications than other tests. Serious harm from colonoscopy appears to be about ten times more common (3.1 per 1000 procedures) than with flexible sigmoidoscopy (3.4 per 10,000 procedures).
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%.
CT virtual colonoscopy [CTVC]
Published reports on CT virtual colonoscopy (CTVC) screening suggest at least comparable sensitivity to colonoscopy for CRC and large polyps (10 mm or larger). CTVC also allows screening for other intra-abdominal abnormalities, but at the expense of a radiation dose.
Faecal Immunochemical Test (FIT)
FIT is a stool test that detects very small amounts of blood in faeces. It is more sensitive than FOBT and is replacing it as part of the National Bowel Cancer Screening Program.
National recommendations United Kingdom
The NHS Bowel Cancer Screening Programme http://www.cancerscreening.nhs.uk/bowel/ 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).