Background: The prevalence of colorectal lesions in persons 40 to 49 years of age, as identified on colonoscopy, has not been determined. Methods: We reviewed the procedure and pathology reports for 906 consecutive persons 40 to 49 years of age who voluntarily participated in an employer-based screening-colonoscopy program. The histologic features of lesions that were identified and removed on endoscopy were categorized according to those of the most advanced lesion removed proximally (up to the junction of the splenic flexure and the descending colon) and the most advanced lesion removed distally. An advanced lesion was defined as an adenoma at least 1 cm in diameter, a polyp with villous histologic features or severe dysplasia, or a cancer. Results: Among those who underwent colonoscopic screening, 78.9 percent had no detected lesions, 10.0 percent had hyperplastic polyps, 8.7 percent had tubular adenomas, and 3.5 percent had advanced neoplasms, none of which were cancerous (95 percent confidence interval for cancer, 0 to 0.4 percent). Eighteen of 33 advanced neoplasms (55 percent) were located distally and were potentially within reach of a sigmoidoscope. If these results are applicable to the general population, at least 250 persons, and perhaps 1000 or more, would need to be screened to detect one cancer in this age group. Conclusions: Colonoscopic detection of colorectal cancer is uncommon in asymptomatic persons 40 to 49 years of age. The noncancerous lesions are equally distributed proximally and distally. The low yield of screening colonoscopy in this age group is consistent with current recommendations about the age at which to begin screening in persons at average risk.
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