Case-control study of screening colonoscopy in relatives of patients with colorectal cancer

The efficacy of colonoscopic screening and polypectomy for the prevention of colorectal cancer (CRC) is well accepted but has never been documented in a prospective, controlled study. Screening by sigmoidoscopy has been found to reduce mortality from cancer of the rectum and distal colon. Case-control studies provide an alternative method for determining the efficacy of screening methods.

Between 1998 and 2000, a total of 40 subjects were found to have CRC (study group) and 160 had a normal colon (control group) among asymptomatic individuals participating in a screening colonoscopy program for a high-risk population of first-degree relatives of CRC patients. We compared these groups for screening by fecal occult blood testing, flexible sigmoidoscopy, barium enema, and colonoscopy in the 10-yr period before the index colonoscopy.

Screening colonoscopy was performed in only 2.5% of the case subjects and 48.7% of controls (p < 0.0001), and all screening procedures in 12.5% and 73.7%, respectively (p < 0.0001). A statistically significant difference was also found for screening with fecal occult blood test, but not for flexible sigmoidoscopy or barium enema. Significant adenomatous polyps >1 cm in diameter were detected and removed in 19% of the control group within 10 yr of the index colonoscopy. Six (15%) of the patients in the study group died of CRC.

Screening by colonoscopy can prevent progression to CRC from adenomatous polyps and may reduce the mortality associated with this devastating disease.