Background: It is often difficult to discriminate between osteosarcoma and malignant fibrous histiocytoma (MFH) of bone, especially in older patients because of the clinical similarities, including the lytic radiologic appearance. A histologic analysis of MFH-like osteosarcoma, which closely resembles MFH of bone both clinically and radiologically, has not yet been conducted thoroughly, and therefore this issue remains controversial.
Methods: Using clinicopathologic and immunohistochemical techniques, the authors studied 24 cases of osteosarcoma arising in patients older than 40 years of age and compared them with 20 cases of MFH of bone from similarly aged patients.
Results: Radiography revealed that 68.2% of the osteosarcoma cases were predominantly lytic, whereas all cases of MFH of bone showed either a predominantly or purely lytic pattern. Histologically, osteosarcoma was subclassified as conventional osteoblastic (54.2%), MFH-like (29.2%) containing various amounts of tumor osteoid and/or bone in each of the cases, and conventional fibroblastic (4.2%), whereas all the cases of MFH of bone had a storiform-pleomorphic pattern. Immunohistochemically, no overexpression of p53 protein was found in MFH-like osteosarcoma, whereas it tended to occur more frequently in osteoblastic osteosarcoma (66.7%) and MFH of bone (50.0%). The Ki-67 labeling index was significantly lower in MFH-like osteosarcoma than in MFH of bone. The 5-year survival rate was 18.2% in patients with osteoblastic osteosarcoma, 66.7% in patients with MFH-like osteosarcoma, and 21.5% in patients with MFH of bone. A significant difference in the survival curve was observed between osteoblastic and MFH-like osteosarcoma.
Conclusions: It is proposed that MFH-like osteosarcoma, which shows characteristically different clinical and histologic features from that of conventional osteosarcoma, thus may be considered a variant of osteosarcoma.