Mixed mesodermal tumor of the ovary: immunohistochemical study with histogenetic consideration

The clinical, histological and immunohistochemical features of three cases of ovarian mixed mesodermal tumor (MMT) were examined. The epithelial component was serous papillary cystadenocarcinoma in case 1 and 3, and endometrioid adenocarcinoma in case 2. In case 1, undifferentiated adenocarcinoma was also seen. The mesenchymal component was fibrosarcomatous and chondrosarcomatous in case 1 and 2. In case 3, only fibrosarcomatous area was seen. No endometriosis was observed. Immunohistochemically, the epithelial component showed positivity for epithelial membrane antigen in all three cases. S-100 protein was positive in two cases with chondrosarcomatous differentiation. The fibrosarcomatous area showed positivity for vimentin in all three cases. However desmin, myosin and myoglobin were negative. The antibodies thought to be epithelial or mesenchymal markers unexpectedly reacted positively in some cells; for example, EMA was positive in fibrosarcomatous and chondrosarcomatous cells. Therefore, it was speculated that because the undifferentiated tumor cells had a biphasic character, MMT might originate from immature multipotential cells of surface epithelium and subcapsular connective tissue of the ovary.