Evolution of colorectal cancer in schistsosomiasis: transitional mucosal changes adjacent to large intestinal carcinoma in colectomy specimens.

In this study of 454 colorectal carcinoma colectomy specimens, (289 were associated with and 165 were unassociated with schistosomiasis. Schistosome infestation was found to play an etiologic role in bowel malignancy in patients having diffuse involvement of the large intestine and a history of ten years or more of colitic symptoms. Diminutive polyps, pseudopolyps, ectopically proliferating glands, disintegrated muscularis mucosae, denudation, and multicentric carcinoma were frequently encountered in the schistosomiasis-associated (SA) group, whereas papillary and adenomatous polyps were most common in the schistosomiasis nonassociated (SN) group. Pseudopolyposis, ectopically regenerating glands, and multicentricity are thought to be predisposing factors in the development of colorectal cancer. This sequence of events is analogous to the development of carcinoma in ulcerative colitis.