Endometrioid proliferative and low malignant potential tumors of the ovary. A clinicopathologic study of 46 cases

We evaluated 41 endometrioid neoplasms with features intermediate between a benign endometrioid tumor and endometrioid carcinoma. Although these tumors showed various degrees of epithelial proliferation, they lacked the destructive stromal invasion of carcinoma. Intermediate endometrioid tumors were subdivided into proliferative endometrioid tumors (PET), endometrioid tumors of low malignant potential (ETLMP), and ETLMP with microscopic areas of invasion. PET were adenofibromas with solid aggregates of epithelial proliferation not exceeding 5 mm in any dimension, whereas ETLMP either had noninvasive cytologically malignant epithelium or aggregates of atypical epithelium measuring at least 5 mm in any dimension uninterrupted by fibromatous stroma. Of the seven PET, five were purely adenofibromatous, while two were mixtures of adenofibromatous and papillary components. Of the 31 ETLMP, 12 were adenofibromatous and 19 were either purely papillary or had mixtures of papillary and adenofibromatous components. An additional three ETLMP had one or more areas of microscopic invasion of the stroma in the form of an irregular or cribriform infiltration by atypical glands, often with squamous differentiation. These three neoplasms were designated 'ETLMP with microinvasive carcinoma'. The only neoplasm with extraovarian implantation at presentation, however, was an ETLMP with mixed adenofibromatous and papillary features, without microinvasion. None of the other patients with ETLMP had a metastasis or developed one within a follow-up period of between 0.8 and 11.2 years. Because they are very low-grade neoplasms, ETLMP should be separated from endometrioid carcinoma and not confused with PET, because PET have no malignant potential.