Ovarian
myxomas recently have been reported as new, distinct pathologic entities that show a myxoid, moderately cellular proliferation of spindle and stellate cells interspersed with areas of
fibrosis,
hemorrhage, and delicate vascular spaces. These histologic features are frequently 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 histologic and immunohistochemical evidence for this proposal, four ovarian
myxomas were compared with 48 primary ovarian stromal
tumors in the
thecoma-
fibroma group from 46 patients. The
thecoma-
fibroma group of stromal
tumors included 23
thecomas, 23
fibromas, and two sclerosing stromal
tumors. We found significant (> 25% of histologic appearance) myxoid change in six
thecomas and one sclerosing stromal
tumor. This myxoid change resembled the histologic appearance of an ovarian
myxoma. Immunohistochemical 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 ovarian
myxomas or in the two sclerosing stromal
tumors, and only three (13%) of the 23
thecomas showed focal staining for
desmin. Nine (39%) of the 23
fibromas expressed
desmin.
S100 protein was expressed in one
fibroma and one
thecoma, weakly. None of the ovarian
myxomas or the
thecoma-
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-
fibroma group of stromal
tumors form a histologic spectrum of lesions in which clear-cut distinguishing points between various entities are difficult to define. The myxoid change, present in the
thecoma-
fibroma group of
tumors, was indistinguishable histologically and immunohistochemically from ovarian
myxoma. For this reason, we propose that ovarian
myxomas may be at one end of the spectrum of differentiation in the
thecoma-
fibroma group of
tumors, in which no remaining stromal
tumor is detectable.