Recently, the category of malignant fibrous histiocytoma (MFH) has been under discussion and new entities resembling MFH have appeared. To clarify the recent situation regarding MFH, we reassessed previously diagnosed MFH cases in accordance with the most up-to-date diagnostic criteria, which included allied tumors. We carefully reassessed 428 cases that had been diagnosed in our institute during the past 28 years. Moreover, we searched for clinicopathological prognostic factors among the cases that were finally diagnosed as MFH. Among the 428 cases, 138 cases had their diagnoses changed. The revised cases included 78 leiomyosarcomas (57%; ordinary leiomyosarcoma, 45 cases; pleomorphic leiomyosarcoma, 23 cases; myxoid leiomyosarcoma, 10 cases), 12 liposarcomas (9%; pleomorphic liposarcoma, 11 cases; dedifferentiated liposarcoma, one case), seven dermatofibrosarcoma protuberans (5%), six unclassified sarcomas (4%), five primary or metastatic carcinomas (4%), four low-grade fibromyxoid sarcomas (3%), four inflammatory myofibroblastic tumors (3%), three rhabdomyosarcomas (2%), three malignant peripheral nerve sheath tumors (2%), three acral myxoinflammatory fibroblastic sarcomas (2%) and two atypical fibroxanthomas (1.5%). Among the 1974 soft tissue sarcomas registered in our institute, MFH (428 cases) had been the most common sarcoma, followed by liposarcoma, leiomyosarcoma and rhabdomyosarcoma. However, after reassessment, leiomyosarcoma proved to be the most common soft tissue sarcoma (322 cases), followed by 290 MFH, 273 liposarcomas and 202 rhabdomyosarcomas. Among these 290 cases finally diagnosed as MFH, survival data were available in 189 cases. Tumor location in the abdominal cavity, the retroperitoneum or the head and neck (P = 0.0024), tumor size of 5 cm or more (P < 0.0001), deep tumor location (P < 0.0001), high histological grade (grade 3) based on the French Federation of Cancer Centers' grading system (P = 0.0007), and high stage (stage III or IV) based on the American Joint Committee on Cancer (AJCC) staging system (P < 0.0001) were significantly worse prognostic factors by univariate analysis. In multivariate analysis, deep tumor location and high AJCC stage were independent adverse prognostic factors. We conclude that leiomyosarcoma is the most important differential diagnosis for MFH, especially pleomorphic leiomyosarcoma from storiform-pleomorphic type and myxoid leiomyosarcoma from myxoid type. Tumor depth and AJCC stage are the most important predictive prognostic factors in MFH.
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