Giant cell tumor of the ovary. Immunohistochemical evidence of origin from stromal ovarian cells.

Giant cell tumor (GCT) of the ovary is a rare condition, found almost invariably in the context of a mucinous tumor and presenting a microscopic picture indistinguishable from GCT of bone. We describe a case of GCT in the wall of a serous cyst of the ovary. An immunohistochemical study was performed using a panel of antibodies to epithelial, mesenchymal and leukocyte antigens. Mononuclear and giant tumor cells were positive for vimentin; CD 68 and LCA were found only in giant cells whereas actin was only found in mononuclear tumor cells. The immunophenotypic profile of the stromal cells of the residual ovary was identical to that of mononuclear tumor cells. The presented data suggest that GCT of the ovary is probably a non-neoplastic lesion of the mesenchymal stromal cells that react against substances of the associated tumor or cyst.