Mucinous metaplasias of the endometrium: Biologically meaningful subsets for the practicing surgical pathologist

Mucinous endometrial metaplasias can be divided into three biologically meaningful subsets based on degree of architectural complexity and cytologic atypia. Type A includes mucin containing epithelial cells which are present singly or in small tufts within architecturally benign glands. Type B is defined as mucin containing epithelial cells forming small pseudoglands with rigid, punched out spaces and no supporting stroma. Type C describes endometrium with conspicuous cytologic atypia or architectural features such as filiform growth pattern. Excluding those cases with coexisting precancerous lesions, endometrial carcinomas were found in 0%, 64.7%, and 100% of follow-up endometrial specimens subclassified into types A, B, and C, respectively.