[Epithelioid smooth muscle tumor of the uterus, of unknown malignant potential]

A uterine smooth muscle tumor belonging to the category of unknown malignant potential in a 20-year-old woman is reported. The major axis of the tumor was 5 cm, and the tumor was soft and homogeneous. Histologically, it was composed of cellular groups, arranged in an epithelioid pattern, with hyaline bands dissecting the groups, moderate nuclear hyperchromasia and pleomorphism, and mitotic index of 2 per 10 high power fields; the tumor had infiltrating margins and tumoral vascular invasions were found. Immunohistochemically, the tumor was positive for vimentin, and negative for keratins, desmin, actin, and S 100 protein. Epithelioid smooth muscle tumors of the uterus should be classified as tumors of unknown malignant potential under the following conditions: if they are larger than 5 cm, if they show at least moderate cellular pleomorphism, if their mitotic index is at least 1 per 10 high power fields, or if they show cellular necrosis. The present immunohistochemical findings suggest more a fibroblastic than a smooth muscle cell origin of this neoplasm.