[Reassessment of the pathological diagnosis in 33 cases of malignant fibrous histiocytoma].

OBJECTIVE: Since malignant fibrous histiocytoma (MFH) may be taken as an undifferentiated pleomorphic sarcoma (UPS), this study was conducted to reassess 33 previously diagnosed MFH cases in the past 10 years based on the latest WHO concept. And then to search for the clinicopathological features, probably tumorigenesis, and the line of differentiation of the remaining MFH/UPS cases.

METHODS: Thirty-three cases in tissue microarray were studied by immunohistochemistry with panels of neurogenic, myogenic, and lipogenic antibodies. Three expertise pathologists reevaluated the slides separately.

RESULTS: Among the 33 cases, 17 cases (51.5%) of MFH had their diagnoses changed, including 5 leiomyosarcomas, 3 malignant peripheral nerve sheath tumors, 1 fibrosarcoma, 1 inflammatory myofibrosarcoma, 1 giant cell tumor and 1 angiomatoid fibrous histiocytoma. The remaining 16 cases (48.5%) were finally diagnosed as MFH/UPS, among which patients were mainly old adults (median age: 63 years; range: 38 to 76 years). The median tumor size was 6.0 cm (range: 3.0 to 14.0 cm), 8 cases (50%) located in lower limb and 5 cases (31.3%) located in thigh. These tumors had marked cytological and nuclear pleomorphism. Immunohistochemistry showed that Vimentin was strongly positive in all 16 MFH/UPS (100%), Muscle-specific actin was variously positive in 8 cases (50%) and 1 case focally expressed Desmin. Eleven cases (68.8%) variously expressed CD68 (KP1) and 7 cases (43.8%) expressed CD68 (PG-M1), which were much higher than leiomyosarcoma, malignant peripheral nerve sheath tumor and liposarcoma with significant difference. Moreover, Ki67 expression rates were from 10% to 100%, including 14 cases more than 50% and 11 cases more than 70%. However, only 2 cases (12.5%) showed P53 positive.

CONCLUSION: MFH/UPS often show marked histological pleomorphism, and the diagnosis must be made by exclusion of other definitive sarcomas, especially myogenic and neurogenic sarcoma. Only Vimentin was always expressed in MFH/UPS, while some of the tumors were positive for myogenic antigen and CD68. It was suggested that MFH/UPS might arise from primary mesenchymal cells, and some cases exhibited fibroblastic and/or myofibroblastic features. In addition, histiocytic phenotypic marker did have more expression in MFH/UPS than in other sarcomas. MFH/UPS still had certain clinicopathological characteristics.