Late development of metachronous colorectal cancer.

The incidence of metachronous colorectal cancer has been reported to be 1 to 5 percent, with most of the cases being discovered within ten years of the initial cancer. A retrospective review of all colorectal cancer patients was conducted at the Southern Illinois University Affiliated Hospitals to determine the incidence of metachronous colorectal cancer at the authors' institution. In this study, a metachronous cancer was defined as a second colorectal primary occurring at least three years following discovery of the initial lesion. Between 1978 and 1984, there were 24 patients with metachronous colorectal cancer identified in an operative series of 707 patients for a frequency of 3.4 percent. These metachronous cancers were discovered at intervals ranging from 3 to 35 years. Sixteen (67%) metachronous lesions occurred 11 years of more after the original cancer. Synchronous or interval adenomatous colorectal polyps were noted in 17 (71 percent) of the patients. Thirteen of the metachronous cancers appeared in the right colon, while six were distributed throughout the transverse and descending colon, and five were in the rectosigmoid region. The incidence of late-appearing metachronous colorectal cancers and the propensity to occur in the right colon underscores the need for evaluation of the entire colon as part of lifelong follow-up of the colorectal cancer patient.