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 t he disease have a high risk of developing colorectal carcinoma. Colono scopic surveillance to detect precancerous tissue and/or cancer in the se 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 Ridd ell's classification, mainly because the intramucosal carcinomas diagn osed by Japanese histopathologists are included in the category of hig h-grade dysplasia in Riddell's classification. Based on the results of a meticulous slide review carried out by seven histopathologists in t his study, a new classification is proposed: UC-I, inflammatory change ; UC-II, indefinite; UC-IIa, probably inflammatory; UC-IIb, probably n eoplastic; UC-III, neoplastic but not carcinomatous; and UC-IV, carcin oma. Intramucosal carcinoma is included in the category UC-IV. We cons ider that the diagnosis of intramucosal carcinoma is to be made when t here is a high grade of cytological and structural atypia consistent w ith carcinoma. Interobserver and intraobserver variability with this c lassification was acceptable. We believe this new classification will be widely use in cancer surveillance in ulcerative colitis in Japan.