Endometrial intraepithelial neoplasia terminology in practice: 4-year experience at a single institution

An alternative WHO classification system for endometrial precancers and hyperplasia separates a lesion called endometrial intraepithelial neoplasia (EIN) from diffuse hormonal effects and cancer, resulting in a 3-category system. EIN is a localized lesion with objective histologic criteria, characterized by monoclonal growth of mutated cells, and associated with a 45-fold elevated cancer risk. This study summarizes our department's experience with EIN diagnoses in the 4 years since conversion to the new terminology. We identified all reports from endometrial samples diagnosed as EIN or including the terms "gland crowding" or "atypia" since conversion and obtained follow-up information from subsequent pathology specimens or clinic notes (82%). The diagnoses were reported by a mixture of pathologists, the majority of whom are not subspecialized to gynecologic pathology and the slides were not reviewed. Overall, 17.1% of women with EIN had carcinoma and 34.9% had either carcinoma or persistent EIN. The proportion of women with EIN or cancer on follow-up did not trend with years since adoption of EIN terminology. The median age at the time of diagnosis was 55 years in an overall population of women who underwent sampling at a median age of 47 years. The median follow-up time was 4 months. All cancers were of endometrioid histology; all but 2 were International Federation of Gynecology and Obstetrics grade 1. In comparison with a previous reproducibility study among expert pathologists on a comparable population from our department, these results for general pathologists show a higher false positive rate for subsequent cancer.