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Histological classification of the neoplastic changes arising in ulcerative colitis: a new proposal in Japan.

Patients with total ulcerative colitis with a longstanding course of the disease have a high risk of developing colorectal carcinoma. Colonoscopic surveillance to detect precancerous tissue and/or cancer in these patients has been carried out in countries with a high incidence of ulcerative colitis. Riddell's classification has been widely used for the interpretation of biopsy specimens obtained from the colonoscopic surveillance. In Japan, however, there are problems in accepting Riddell's classification, mainly because the intramucosal carcinomas diagnosed by Japanese histopathologists are included in the category of high-grade dysplasia in Riddell's classification. Based on the results of a meticulous slide review carried out by seven histopathologists in this study, a new classification is proposed: UC-I, inflammatory change; UC-II, indefinite; UC-IIa, probably inflammatory; UC-IIb, probably neoplastic; UC-III, neoplastic but not carcinomatous; and UC-IV, carcinoma. Intramucosal carcinomas is included in the category UC-IV. We consider that the diagnosis of intramucosal carcinoma is to be made when there is a high grade of cytological and structural atypia consistent with carcinoma. Interobserver and intraobserver variability with this classification was acceptable. We believe this new classification will be widely use in cancer surveillance in ulcerative colitis in Japan.