Screening for colorectal cancer.

Considerable indirect evidence, based on the natural history of colorectal cancer and the ability of tests to detect adenomas and invasive cancers, suggests that screening for colorectal cancer reduces mortality. Without screening, a 50-year-old person at average risk has approximately a 530-in-10,000 chance of developing invasive colorectal cancer in the rest of his or her life and approximately a 250-in-10,000 chance of dying from it. Analysis of indirect evidence with a mathematic model indicates that screening persons for 25 years, from the age of 50 to the age of 75 years should reduce the chance of developing or dying from colorectal cancer by 10% to 75%, depending on which screening tests are used and how often screening is done. Screening for colorectal cancer is optional. A possible recommendation is that annual fecal occult blood tests and 65-cm flexible sigmoidoscopy every 3 to 5 years be done for average-risk men and women who are between 50 and 75 years of age. In addition to having annual fecal occult blood tests, persons with first-degree relatives with colorectal cancer can be offered barium enemas instead of sigmoidoscopies every 3 to 5 years.