Endometrial stromal sarcoma with sex cord-like areas and focal rhabdoid differentiation.

An unusual uterine lesion is described in a patient with postmenopausal bleeding. Grossly, a yellow, polypoid mass projected into the uterine cavity. Histological examination showed a distinct biphasic pattern with areas of typical low-grade endometrial stromal sarcoma and areas where tumour cells were arranged in cords and trabeculae, resulting in a sex cord-like pattern. In these areas the cells assumed a rhabdoid morphology with eccentric vesicular nuclei, prominent nucleoli and eosinophilic hyaline cytoplasmic inclusions. Immunohistochemistry showed positive cytoplasmic staining of both components for vimentin, desmin and the cytokeratin marker CAM 5.2, but no staining for CEA and EMA. Electronmicroscopy revealed prominent paranuclear arrays of intermediate filaments. This is the second reported case of endometrial stromal sarcoma with rhabdoid differentiation and the first documented example of rhabdoid cells in sex cord-like areas. The report adds to the list of diverse neoplasms which may display a characteristic rhabdoid morphology and supports the hypothesis that extrarenal rhabdoid tumours are not a distinct clinicopathological entity. A diagnosis of malignant rhabdoid tumour of the uterus should be considered only when extensive sampling fails to disclose areas with an appearance typical of an endometrial stromal lesion.