Variants of in situ carcinoma of the endometrium: Clear cell and gastrointestinal types, with a review of the literature.

Two precursor lesions are commonly associated with endometrial carcinoma. Atypical endometrial hyperplasia/endometrial intraepithelial neoplasia is a known precursor lesion of endometrial endometrioid carcinoma, while endometrial intraepithelial carcinoma, is a recognized precursor lesion of endometrial high-grade serous carcinoma. Other than these two recognized entities, other rare precursor lesions for endometrial carcinoma do exist, although reported cases are relatively few and not universally recognized. This therefore poses diagnostic challenges in clinical practice. Here, we describe a series of rare precursor lesions of the endometrium identified at our institution, including clear cell and gastrointestinal variants, their morphologic and immunohistochemical characteristics, and review current literature regarding these variants. The information provided may guide the proper diagnosis and ultimately lead to effective clinical management in every-day practice.