Etiologic insights from surface adjustment of colorectal carcinoma incidences: an analysis of the U.S. SEER data 2000-2004.

Abstract

The subsite-specific comparison of the incidence of carcinoma within the colorectum is complicated because the mucosal surface, and therefore the amount of epithelial cells at risk, varies among the subsites. The aim of this study was to provide the subsite-specific estimates of the colon mucosal surface and the mucosal surface-adjusted carcinoma incidence estimates of colon subsites that allow a more valid comparison of the subsite-specific incidences. We extracted subsite-specific incidence rates of colorectal carcinoma from the Surveillance, Epidemiology, and End Results (SEER) Program of the years 2000-2004. The rates were age-standardized to the U.S. standard population in the year 2000. We estimated the mucosal surface of each segment of the colorectum and calculated the surface-adjusted incidence rates by dividing the observed age-standardized incidence rates by the estimated surface areas. After adjustment for surface area, the incidence relations among the colorectal subsites changed. Within the colon, the surface-adjusted rates tend to be highest in the cecum, followed by the vermiform appendix, ascending colon, and sigmoid colon. The rates of the transverse and descending colon are considerably lower. The surfaced-adjusted incidence of rectal carcinoma is about 12- to 23-fold higher than the rate of carcinoma of the transverse colon. The distribution of the incidence of carcinomas is markedly influenced by the adjustment of surface area of the colorectum. Similar surface-adjusted rates of the vermiform appendix and ascending colon may implicate that these subsites share a similar etiology. Considerable differences of the surface-adjusted rates of the sigmoid colon and rectum may indicate different etiologies of carcinomas of these subsites.