Detection and prevention of colon cancer by colonoscopy.

It is widely accepted that most carcinomas of the colon and rectum develop through the adenoma-to-carcinoma sequence. A recent review characterizes the various relationships between colorectal polyps and carcinoma. Tierney and Associates list several studies that show the frequent coexistence of adenomatous polyps with carcinoma of the colon or rectum. The incidence of polyps in patients with carcinoma of the colon and rectum ranges from 12.9% to 62%. Retrospective reports show a lower incidence of polyps in patients with carcinoma of the colon or rectum (13.7% to 23%). However, colon segments resected for carcinoma of the colon have a significant incidence of associated adenomatous polyps (15% to 28%). In patients with carcinoma of the colon or rectum undergoing preoperative fiberoptic colonoscopy there is a percentage of polyps larger than 5mm in diameter ranging between 36% and 62%. There is also a higher rate of both synchronous and metachronous carcinomas in patients in whom polyps coexist with the primary malignant lesion. The rate of metachronous carcinomas in patients with associated polyps at the time the first tumor was discovered is reported to be twice as great as for patients who did not have polyps (2.6% versus 1.14%, respectively). Synchronous malignant lesions were detected in 11% of patients with polyps but in only 0.7% of patients without polyps. In patients with multiple polyps coexistent with the original carcinoma, synchronous malignant lesions are found in 14.6% of patients and metachronous malignant lesions developed in 12.4%.(ABSTRACT TRUNCATED AT 250 WORDS)