Morphogenesis and development of superficial spreading tumor of the colon and rectum

The aim of this study was to clarify the morphogenesis and mechanism of a wide intramucosal extension of a superficial spreading (epithelial) tumor (SST; defined as an epithelial tumor with wide intramucosal spreading involving a diameter of 30 mm or more) in the colon and rectum. For this purpose favorable sites, histological components, and histological growth patterns were compared between 95 cases of SST (16 adenomas and 79 carcinomas) and 2356 non-SST cases, which served as controls. The frequency of SST was significantly higher in the cecum and rectum, and lower in the sigmoid colon when compared to the locations of the control. Among the SST cases, 82.3% of superficial spreading carcinoma (SSC) had an adenomatous component and 96.2% had a cytologically low-grade carcinoma (CAL). In intramucosal SSC, the adenomatous and/or CAL component was predominant, and the proportion of high-grade carcinoma (CAH) was significantly smaller in intramucosal SSC in comparison with the control group. In the mucosal spreading area of SST, 78.9% were tubulovillous in histological type and 86.3% showed a replacing growth pattern. These results indicate that an SST initially develops as an adenoma in at least 85.3% of cases and CAL in 14.7% cases at most; spreads superficially in the mucosa by a replacing growth mechanism that forms a tubulovillous and villous structure; and is affected by intestinal peristalsis less than non-SST.