Malignant fibrous histiocytoma of the lung.

A 75-year-old woman was admitted to a hospital for diagnosis of pulmonary infarction and died during treatment. An autopsy revealed a tumor 5 cm in diameter in the hilus of the left lung, spreading into the posterior mediastinum, and a metastasis was also found in the right lung. Histologically, this tumor consisted of two kinds of cells; one of fibroblast-like cells and the other of histiocyte-like cells, showing a storiform pattern. Furthermore, a positive staining for alpha 1-antitrypsin, but negative for CEA, keratin or S-100 protein was seen. Therefore, it was diagnosed as malignant fibrous histiocytoma (MFH) originating in the hilus of the left lung. In addition, many foci of hemorrhagic infarction due to metastasis and infiltration of the tumor into the pulmonary arteries were observed in the right lung. MFH is one of the rarest primary tumors of the lung.