Evidence supporting colorectal screening, aside from randomised trials of faecal occult blood testing, comes mainly from observational studies. In the linked paper (doi:10.1136/bmj.b1846) interim results of the Norwegian Colorectal Cancer Prevention (NORCCAP) trial are presented.1 NORCCAP is one of three ongoing trials of once only screening sigmoidoscopy.1 2 3 The findings suggest that the intervention may be effective in reducing mortality from colorectal cancer.

The NORCCAP trial randomised 55 736 people aged 55-64 years to usual care or to once only flexible sigmoidoscopy with or without a single round of immunochemical faecal occult blood testing. The primary outcome for this first report is 7 year cumulative incidence of colorectal cancer (anywhere in the colon); the secondary outcome is 6 year mortality from colorectal cancer. Colonoscopy, which was done in 21% of patients screened, was recommended for people with a positive screening result, defined as any polyp 10 mm or larger in diameter, any histologically verified adenoma or carcinoma, or a positive faecal occult blood test. Follow-up was obtained from the Cancer Registry of Norway and the Norwegian Cause of Death Registry, both of which …