Malignant fibrous histiocytoma of the lung.

Two malignant fibrous histiocytomas arising primarily in the lung are described. The first was a large tumor of the right lower lobe in a 53-year-old man. The other tumor was found incidentally on routine roentgenograms in a 25-year-old woman and involved the left main pulmonary artery. The lesions could be resected but both patients developed early cerebral metastases. The neoplasms were predominantly fibroblastic, had a characteristic storiform pattern, and included large histiocytes with bizarre nuclei and a vacuolated cytoplasm. The ultrastructure of the cells in the fibroblastic areas was characterized by irregular nuclei and a cytoplasm with a well-developed endoplasmic reticulum and dilated cisternae. Some cells lacked the prominent endoplasmic reticulum of fibroblasts and others were characteristic histiocytes with numerous cytoplasmic lysosomes. The cases appear to be the first reported primary malignant fibrous histiocytomas of the lung.