Carcinosarcoma (malignant mixed müllerian (mesodermal) tumor) of the female genital tract: immunohistochemical and ultrastructural analysis of 28 cases.

In an attempt to clarify the histogenesis of carcinosarcoma (malignant mixed müllerian tumor) of the female genital tract, 20 uterine and eight ovarian tumors were studied by light microscopy, transmission electron microscopy, and immunohistochemistry. Cytokeratins (MAK-6 and AE1:AE3) and epithelial membrane antigen were detected in the epithelial component of all tumors and in the stromal component of 15 cases (55%). Vimentin was detected in the stromal component of all cases and was focally positive in the epithelial component of 18 cases (69%). Tumors showing rhabdomyosarcomatous or chondrosarcomatous differentiation were positive for myoglobin and S-100 protein, respectively. At the ultrastructural level epithelial cells were observed in tight clusters (usually surrounded by a basal lamina), in loose aggregates, and singly (sometimes spindle shaped), and were surrounded by cells displaying variable differentiation. The closest examples of "hybrid" epithelial/stromal cells were those with a prominent rough endoplasmic reticulum, cytoplasmic projections, poorly formed intercellular junctions, and an incomplete basal lamina. The observations support the view that carcinosarcomas of the female genital tract could represent examples of biphasic (metaplastic) carcinomas.