Malignant fibrous histiocytoma with special reference to its differential diagnosis.

The histological diagnosis of malignant fibrous histiocytoma (MFH) seems to have become recently fashionable among pathologists, although its histogenesis and diagnostic criteria are not entirely settled as yet. For practical purposes the differential diagnosis with other easily mistakable mesenchymal tumors should be strictly made with great caution, because of variable histological features of this tumor. The authors attempted to elucidate the differential points from other tumors in a review of 189 cases of malignant soft tissue tumors. Some cases of carcinoma mimicking MFH were also reviewed. No single criterion for making the histological diagnosis of MFH was obtained. Its histological features and differential points from pleomorphic rhabdomyosarcoma and fibrosarcoma were tabulated. The recognition of a true tumor osteoid was emphasized as a single differential point between osteosarcoma and MFH often with fibrous areas mimicking osteoid. Renal cell carcinoma metastasizing to bone, which was misinterpreted as MFH on biopsy tissue, was also described and its differential point was stated.