A 66-year-old woman had noticed a nodule on her light groin 15 years ago. The nodule was excised two times because of recurrence. She came to our hospital because of a 3rd recurrence occurred. The nodule was widely excised with 5cm margins. Histopathologically, the tumor was mainly composed of spindle-shaped cells. In some areas of the lesion, the tumor cells were arranged in a storiform pattern, and in other areas myxoid changes were seen. Immunohistochemical study revealed that the tumor cells were positive for vimentin, factor XIII a, but negative for keratin, α-SMA, tdesmin, S-100, factor VIII, CD34 and EMA. Ultrastructurally, the tumor cells had a fibroblastic phenotype. Thus we diagnosed this tumor as malignant fibrous histiocytoma, myxoid type. Subsequently, a nodule had appeared on her forehead 2 years after the operation. Histopathologically, the nodule was diagnosed as myxoma, whereas the tumor which recurred about l year after the first operation was diagnosed as myxoid-MFH. One year later the tumor has recurred again; no systemic metastasis was detected. Recently it has been emphasized that, in most cases originally diagnosed as MFH, a specific line of differentiation is evident, and relatively few cases have to be classified as MFH or not otherwise specified. We assume that this case is myxofibrosarcoma rather than myxoid-MFH, because ultrastracturally, the tumor cells of this case were composed of only fibroblastic phenotype, and generally MFH reveals a more aggressive course than this case. [Skin Cancer (Japan) 2003; 18: 259-265]
