Prevalence of distal colonic neoplasia associated with proximal colon cancers

The number, size, and histologic features of distal colorectal adenomatous polyps have been reported to correlate with the risk of developing proximal colon cancer. To investigate this putative relationship further, we evaluated the frequency of distal colorectal neoplastic polyps in patients with colon cancer located proximal to the splenic flexure.

All cases of colorectal adenocarcinomas treated at a tertiary referral center and Veterans Affairs hospital between 1979 and 1992 were identified by International Classification of Diseases coding and review of pathology and colonoscopy reports. The medical records of patients with documented cancers proximal to the splenic flexure were examined for the presence, location, size, and histopathologic features of synchronous neoplastic lesions found at colonoscopy.

Among 634 patients with colorectal cancer identifiable by location, 172 had proximally located tumors. Of these, 60 patients were excluded because of lack of complete colonoscopy or because surgical resection was performed elsewhere. Forty percent of the remaining 112 patients for whom data could be evaluated demonstrated neoplastic lesions in addition to the proximal cancer. The colon was devoid of "sentinel" neoplasia distal to the splenic flexure and descending colon-sigmoid colon junction in 69% and 72% of patients, respectively.

The majority of proximal colon cancers are not associated with distal sentinel lesions. We surmise that flexible sigmoidoscopy will fail to find evidence of neoplasia in at least 25% of patients with prevalent colon cancers.