Myxofibrosarcoma with an infiltrative growth pattern: a case report.

Myxofibrosarcoma, also known as a myxoid variant of malignant fibrous histiocytoma, is one of the most common sarcomas in the extremities of elderly people and is characterized by a high frequency of local recurrence. We report a case of myxofibrosarcoma, intermediate grade, involving the thigh along the fascial plane and between the muscles without the formation of an apparent nodular lesion. On microscopic examination, the tumor lacked areas of necrosis and pronounced cellular pleomorphism, but it was highly cellular with proliferation of spindle cells which contained large elongated, hyperchromatic and irregularly shaped nuclei, slightly eosinophilic cytoplasm and indistinct cell margins, arranged in both interlacing fascicles and a storiform pattern. Immunohistochemically, many of the tumor cells showed intense reactivity to vimentin and CD34. More than 20% of the cells were positive for p53 protein and the MIB-1 labeling index was approximately 30%. Desmin, alpha-smooth muscle actin, muscle-specific actin, S-100 protein, cytokeratin, epithelial membrane antigen, bcl-2 protein and neurofilament were negative. The absence of a discrete mass lesion and diffuse infiltrative nature precluded early recognition of tumor. Seven years after hindquarter amputation, the patient has been alive without evidence of local recurrence or distant metastasis. This case indicates that myxofibrosarcoma can demonstrate a highly infiltrative growth pattern. It is possible that this infiltrative nature is associated with a high rate of local recurrence of the tumor. A careful radiological examination of the extension of the tumor prior to surgery is mandatory considering the infiltrative nature of myxofibrosarcoma.