Malignant fibrous histiocytoma of bone. A clinico-pathological and electronmicroscopical study

The clinicopathological and ultrastructural features of seven Malignant Fibrous Histiocytomas reported to the Spanish Registry of Bone Tumors were studied. Two patients were females (20 and 60 years old) and the other five males (15, 37, 67, 38 and 17 years old). The tumors were located in the lower femur (3 cases), upper tibia, upper humerus, rib and iliac bone. The past medical history revealed previous fracture in one patient and previous radiation of the affected bone in another; in a third patient the tumor associated to a bone infarct. Microscopically all tumors presented a storiform pattern composed of neoplastic fibroblasts, histiocytes, and malignant multinucleated giant cells. There was no evidence of osteoid or bone tissue formation by the tumor cells. Five cases were studied with electronmicroscopy; the tumor cells had features of fibroblasts, myofibroblasts, histiocytes and multinucleated histiocytes. Primary and secondary lysosomes, along with lipid vacuoles were common findings in the tumor cells. The value of the electron-microscopy in the differential diagnosis of this tumor is emphasized.