Primary malignant fibrous histiocytoma of the pleura. A case report.

A rare primary malignant fibrous histiocytoma of the pleura is described. The tumor was found in an elderly male and was followed for more than ten years without treatment. At the terminal stage, the patient developed a malignant pleural effusion, which contained mainly histiocytelike, rounded forms with many bizarre and multinucleated giant tumor cells. The main tumor mass was characterized by dual fibroblastlike and histiocytelike cellular components and a storiform growth pattern. In the solid areas, the tumor cells were mainly fibroblastlike spindle-shaped forms, which produced collagen. The tumor cells in the loose, vascular areas and in the effusion were predominantly histiocytelike, with some exhibiting phagocytic activity. We believe that this is the first reported case of a malignant fibrous histiocytoma of the pleura with a malignant effusion showing a preferential histiocytelike differentiation of tumor cells in the fluid environment.