Low-grade myxofibrosarcoma: progression in recurrence.

A case of low-grade myxofibrosarcoma with histologic progression in recurrence occurring in a 51-year-old male is described. The patient had a well-circumscribed encapsulated myxoid mass, which measured 2.5 cm at its greatest diameter, in the subcutis of the left forearm. Microscopically, the tumor was characterized by a proliferation of sparsely distributed spindle or stellate cells, curvilinear small vessels and myxoid stroma. It demonstrated mild pleomorphism without mitotic figures. The patient had the first recurrence at 3 years, which was histologically identical to the primary tumor. The patient had a second recurrence at 11 years, which was predominantly composed of sheets of anaplastic, rounded or oval cells with focal osteoid formation. Immunohistochemically, the tumor cells in the primary and the first recurrent lesions were focally positive for vimentin. In the second recurrence, the tumor cells contained vimentin, alpha-smooth muscle actin and muscle specific actin (HHF35). The primary lesion had a diploid DNA content with low S-phase fractions. The second recurrence showed a polyploidy. The patient was well with no evidence of disease 18 months after the second recurrence. These findings suggest that this neoplasm showed histological progression with an increasing risk of metastasis. Low-grade myxofibrosarcoma, which commonly is misinterpreted as benign, has a tendency for histological and biological progression in local recurrences, underlining the importance of accurate diagnosis and wide surgical excision of the primary lesion.