Primary tumor of spleen with morphologic features of malignant fibrous histiocytoma. Immunohistochemical evidence for a macrophage origin.

We report a case of primary splenic malignant fibrous histiocytoma that occurred in a 41-year-old man. Adjacent to the tumor there was a large calcified intrasplenic cyst. Despite splenectomy, postoperative radiation, and systemic chemotherapy, the patient died with metastatic tumor 6 months after diagnosis. Electron microscopic analysis of the tumor demonstrated subpopulations of tumor cells with fibroblastic or histiocytic features. Immunoperoxidase studies of frozen tumor tissue showed positive staining of both spindle and histiocytelike tumor cells with a large panel of monoclonal antibodies against antigens associated with the mononuclear phagocyte system. Expression of these antigens by the tumor supports a mononuclear phagocyte origin.