Sigmoidoscopy screening probably works, but how well is still unknown.

The most persuasive scientific evidence for the benefit of a cancer screening test comes from a randomized controlled clinical trial (RCT) where the endpoint is a reduction in mortality from (or incidence of) the disease of interest. There have been three RCTs of a fecal occult blood test (Hemoccult; Beckman Coulter, Palo Alto, CA) for early detection of colorectal cancer involving more than 250 000 people that have shown consistent results (1–5). Unfortunately, for the other colorectal cancer screening methods (i.e., sigmoidoscopy, colonoscopy, virtual colonoscopy, barium enema, and other fecal occult blood tests), there is no adequately completed trial that provides a valid estimate of the effect of screening. RCTs are currently underway to evaluate sigmoidoscopy (6,7), and a pilot study has been implemented to examine the benefits associated with a one-time colonoscopy (8). Of the tests that have not undergone adequate