Endometrial intraepithelial neoplasia classification

Overview
The EIN diagnostic schema is intended to replace the previous "endometrial hyperplasia" classification as defined by the World Health Organization in 1994, which have been separated into benign (benign endometrial hyperplasia) and premalignant (EIN) classes in accordance with their behavior and clinical management. EIN should not be confused with an unrelated entity, serous intraepithelial carcinoma ("serous EIC"), which is an early stage of a different tumor type known as papillary serous adenocarcinoma that also occurs in the same location within the uterus.

Disease classes that need to be distinguished from EIN
The spectrum of disease which must be distinguished from EIN (Table II) includes benign endometrial hyperplasia and carcinoma: Table II: Disease classes that need to be distinguished from EIN.