HISTOLOGIC AND IMMUNOHISTOCHEMICAL EVIDENCE FOR CONSIDERING OVARIAN MYXOMA AS A VARIANT OF THE THECOMA-FIBROMA GROUP OF OVARIAN STROMAL TUMORS

Ovarian myxomas recently have been reported as new, distinct pathologi c entities that show a myxoid, moderately cellular proliferation of sp indle and stellate cells interspersed with areas of fibrosis, hemorrha ge, and delicate vascular spaces. These histologic features are freque ntly seen in the thecoma-fibroma group of ovarian stromal tumors. For this reason, we propose that ovarian myxomas are part of the spectrum of differentiation in thecomas-fibromas of the ovary. To provide histo logic and immunohistochemical evidence for this proposal, four ovarian myxomas were compared with 48 primary ovarian stromal tumors in the t hecoma-fibroma group from 46 patients. The thecoma-fibroma group of st romal tumors included 23 thecomas, 23 fibromas, and two sclerosing str omal tumors. We found significant (>25% of histologic appearance) myxo id change in six thecomas and one sclerosing stromal tumor. This myxoi d change resembled the histologic appearance of an ovarian myxoma. Imm unohistochemical studies on paraffin-embedded material showed vimentin immunostaining in all tumors. Smooth-muscle actin was present in all of the myxomas, in two of the two sclerosing stromal tumors, and in 20 (90%) of the 23 thecomas, but it was present in only 11 (48%) of the 23 fibromas. Desmin staining was not present in any of the four ovaria n myxomas or in the two sclerosing stromal tumors, and only three (13% ) of the 23 thecomas showed focal staining for desmin. Nine (39%) of t he 23 fibromas expressed desmin. S100 protein was expressed in one fib roma and one thecoma, weakly. None of the ovarian myxomas or the theco ma-fibroma group of stromal tumors expressed cytokeratins as detected by three different monoclonal antibody cocktails, ie, cytokeratin AE1/ AE3, cytokeratin CAM 5.2, or cytokeratin MAK-6. The ovarian thecoma-fi broma group of stromal tumors form a histologic spectrum of lesions in which clear-cut distinguishing points between various entities are di fficult to define. The myxoid change, present in the thecoma-fibroma g roup of tumors, was indistinguishable histologically and immunohistoch emically from ovarian myxoma. For this reason, we propose that ovarian myxomas may be at one end of the spectrum of differentiation in the t hecoma-fibroma group of tumors, in which no remaining stromal tumor is detectable.