Epithelioid endometrial and endometrioid stromal tumors: a report of four cases emphasizing their distinction from epithelioid smooth muscle tumors and other oxyphilic uterine and extrauterine tumors.

Three endometrial and one extrauterine endometrioid stromal tumors (three sarcomas and one stromal nodule) with a prominent component of epithelioid cells with abundant eosinophilic cytoplasm are described. The patients were 39, 48, 56 and 86 years of age. The endometrial sarcomas were described grossly as an ill-defined tan nodule and "ragged and papillary," respectively, and had the typical infiltrative pattern of low-grade endometrial stromal sarcoma. The stromal nodule was a 13-cm, well circumscribed, yellow, fleshy mass. The extrauterine tumor was probably primary in the sigmoid colon. Oval to polygonal epithelioid cells with abundant eosinophilic cytoplasm accounted for 50% to 90% of the tumor cells. The cytoplasm was granular in one case. None of the tumors contained cells with a rhabdoid appearance. Nuclear and other features did not differ from those of usual endometrial-endometrioid stromal tumors except in one case in which there was greater nuclear pleomorphism. There was strong diffuse cytoplasmic immunoreactivity of all four tumors for vimentin and for CD10 in three of three tumors tested, as well as extensive and moderate reactivity for NK1/C3 and focal weak reactivity for CD68 in two of three tumors tested. Muscle actin positivity was very focal to extensive and weak to strong in all three tumors tested, mainly in the epithelioid areas; alpha-smooth muscle actin was focally to extensively positive in the epithelioid areas of two of three tumors tested; and focal strong desmin positivity (interpreted as indicating smooth muscle metaplasia) was found in the epithelioid areas of one of four tumors. A vaginal recurrence in one case had similar cytologic features to the primary tumor but when examined initially in the absence of adequate history posed diagnostic difficulty, as did evaluation of the uterine tumor in two other cases and the extrauterine tumor in the final case. The differential in these cases is primarily with an epithelioid smooth muscle tumor when they are uterine primaries. The typical infiltration facilitates this distinction in the cases of endometrial stromal sarcomas, but this feature is usually only evident in hysterectomy specimens. In limited samples such as biopsy or curettage specimens, and in some cases of recurrent tumor, awareness that endometrial-endometrioid stromal tumors can have epithelioid cells is crucial in the formulation of the differential diagnosis. Diverse oxyphilic tumors, including deciduoid malignant mesothelioma, can potentially be in the differential diagnosis with extrauterine (endometrioid) stromal sarcomas with epithelioid cells. Immunohistochemical evaluation may potentially provide major aid in diagnosis.