Malignant fibrous histiocytoma of the heart.

An autopsied case of malignant fibrous histiocytoma (MFH) in the left atrium of the heart of a 29-year-old Japanese woman was reported light and electron microscopically, and immunohistochemically. Metastasis was found in the adrenal, jejunum, and cervical regions. This is the fourth case of MFH of the heart in the literature. The tumor consisted of undifferentiated mesenchymal cells and histiocytoid cells, including giant cells and xanthomatous cells. Dense patches were commonly detected in all tumor cells. On frozen sections, histiocytoid cells formed EA and EAC rosettes, while fibroblastic cells formed EA rosettes only. Difference between them was also recognized in activity or amount of marker enzymes of histiocytes. These analyses suggested that MFH is a mesenchymal cell tumor with binary differentiation into histiocytoid cells and fibroblastic cells.