Distribution of colorectal neoplasms. A left to right shift of polyps and cancer.

A 20-year retrospective review was made of all patients undergoing operative procedures for both adenocarcinoma and benign polyps of the colorectum at the two teaching hospitals of the University of South Carolina. A total of 1,112 patients with adenocarcinoma and 429 patients with benign polypoid disease were identified. Classification of each adenocarcinoma according to location showed a 12 per cent increase in the number of right-sided lesions and a 44 per cent decrease in rectosigmoid lesions when compared with historical series. Despite this proximal shift, the rate of association of benign adenomatous polyps contained in cancer resections (13 per cent) is similar to previous series. Furthermore, evaluation of benign adenomatous polyps showed a similar increase of proximal colonic lesions and a decrease of rectosigmoid adenomas. The results of this retrospective study support the concept that adenocarcinoma is occurring with increasing frequency in the right colon. Despite this left to right shift, a constant association of benign polyps within cancer resections was found, supporting the concept of a polyp-cancer sequence. This study identified a similar shift in benign adenomatous polyps alone, supporting the concept that benign neoplasias are premalignant and are probably responsible for the increased incidence of proximally located colonic adenocarcinomas.