Background. Colorectal cancer incidence rates vary widely internationally, by race and gender, and have changed over time. Investigation of the patterns by subsite within the colorectum may suggest clues of possible etiologic significance for further study.
Methods. Using population-based data on more than 120,000 cases diagnosed 1976-1987 in the United States Surveillance, Epidemiology, and End Results program, colorectal cancer incidence was evaluated by subsite of origin.
Results. Little racial variation was evident for cecum and ascending colon cancers; rates were higher among blacks than whites for transverse and descending colon cancers but lower for sigmoid, rectosigmoid, and rectal cancers. Rates generally increased over time for most colon sites, especially sigmoid colon among white men, but declined slightly for rectal cancer among whites. The sex ratio increased among whites monotonically from 1.12 for cecum to 1.71 for rectal cancers. The distal colon cancer excess among men was most notable at older ages, contrasting with slightly higher rates among women at younger ages. Geographic differences were particularly notable for transverse and rectosigmoid colon cancers.
Conclusions. It may be fruitful for future studies to evaluate factors affecting colorectal carcinogenesis by subsite of origin.