Periodic health examination, 1994 update: 2. Screening strategies for colorectal cancer. Canadian Task Force on the Periodic Health Examination.

OBJECTIVE

To make recommendations on the effectiveness of screening for colorectal cancer in asymptomatic patients over 40 years of age.

OPTIONS

Multiphase screening that begins with test for fecal occult blood, uniphase screening with sigmoidoscopy and uniphase screening with colonoscopy. Options included screening repeated at different intervals and different procedures for patients with selected risk factors.

OUTCOMES

Rates of death, death from cancer and cancer detection; compliance, feasibility and accuracy of each manoeuvre.

EVIDENCE

A MEDLINE search for articles published between January 1966 and June 1993 with the use of MeSH terms "screening" and "colorectal neoplasia," a check with the reference sections of review articles published before June 1993 and a survey of content experts. Articles were weighted according to the Canadian Task Force on the Periodic Health Examination levels of evidence.

VALUES

The highest value was assigned to manoeuvres that lowered the rate of death from cancer and had a low rate of false-positive results and acceptable cost and compliance. Recommendations were determined by consensus of the authors, members of the task force and colorectal cancer experts.

BENEFITS, HARMS AND COSTS: There is evidence that annual fecal occult blood testing with the use of the rehydrated Hemoccult test has a small but significant benefit in lowering the rate of death from cancer after more than 10 years of screening; however, the high rate of false-positive results (9.8%) and the poor sensitivity of annual (49%) and biennial (38%) screening make this a poor method for detecting colorectal cancer. There is fair evidence that screening with sigmoidoscopy may improve survival rates; however, this may be due to volunteer bias. The high cost of and poor compliance with colonoscopic screening make this an unfeasible strategy.