Fibroblastic/myofibroblastic sarcoma of the skin: a report of five cases

BACKGROUND: A number of malignant soft tissue tumors, particularly those of fibroblastic and fibrohistiocytic derivation, have been found to display myofibroblastic differentiation focally. The term myofibroblastic sarcoma, a controversial presumably distinctive entity, defines a malignant soft tissue tumor in which myofibroblasts are quantitatively the predominant cell type. METHODS: Five cases of cutaneous spindle-cell sarcomas showing fibroblastic-myofibroblastic differentiation with predominance of fibroblasts were retrieved from the files of three large centers of dermatopathology. Tumors were analyzed histopathologically, immunophenotypically, and, in two cases, ultrastructurally. Results were compared with those previously reported in fibrosarcoma, malignant fibrous histiocytoma, and myofibroblastic sarcoma. RESULTS: Immunophenotypic and ultrastructural profiles of the cases analyzed in this series were closer to fibrosarcoma and to malignant fibrous histiocytoma than to myofibroblastic sarcoma by virtue of quantitative predominance of fibroblasts over myofibroblasts. On the other hand, histopathologic findings were in keeping with those reported in myofibroblastic sarcoma. CONCLUSIONS: Our series highlights the intrinsic problems in attaching certain cutaneous sarcomas with fibroblastic-myofibroblastic differentiation to one of the recognized entities and gives support to the hypothesis that fibrosarcoma, malignant fibrous histiocytoma, and myofibroblastic sarcoma are related histogenetically.