Abstract
Extrarenal malignant rhabdoid tumors have been reported in a variety of anatomic sites but infrequently in the female genital tract. In the uterus, they have been described as a pure tumor, in association with endometrial stromal sarcomas, and as a component of a malignant mullerian mixed tumor. This study reports an unusual uterine neoplasm in a 49-year-old woman, in which a malignant rhabdoid tumor occurred as a collision tumor with a well-differentiated endometrioid adenocarcinoma. The tumor was a 14-cm polypoid mass that filled the endometrial cavity. The two neoplastic components were distinct on microscopic and immunohistochemical examination. Ultrastructural examination confirmed the rhabdoid phenotype of the sarcomatous component. The patient died of disease 4 months after diagnosis with progression of the malignant rhabdoid tumor. The highly aggressive behavior of the rhabdoid (i.e., nonepithelial) component in this collision tumor lends support for a distinction of this neoplasm from a malignant mullerian mixed tumor, with which it may be confused.