Expression of glial fibrillary acidic protein by neoplastic cells of Müllerian origin

Immunocytochemical studies of malignant mixed Mullerian tumors revealed the presence of neoplastic cells showing strong immunoreactivity for glial fibrillary acidic protein, a protein specific for astrocytes, in 9 of 13 cases. Undifferentiated malignant tumor cells of endometrial stromal sarcoma and astrocytes in glioma of the uterus also demonstrate GFAP immunoreactivity. GFAP immunostaining in these neoplastic cells is highly specific and shows no cross-reactivity with cytokeratin, actin, myoglobin, epithelial membrane antigen or factor VIII. It is postulated that the GFAP immunostaining within neoplastic cells of Mullerian origin may be (a) a reflection of the phenotypic diversity of intermediate filament proteins that can be expressed by malignant neoplastic cells, (b) that the polypeptides of GFAP may be heterogeneous, (c) that there may be an ontogenic relationship between the cells of Mullerian origin and neuroectodermal cells, or (d) that this may represent neometaplasia of Mullerian cells.