[Low grade fibromyxoid sarcoma: a clinico-pathologic analysis of 7 cases]

Low-grade fibromyxoid sarcoma (LGFMS) is a malignant soft tissue tumor. Despite bland histologic features, a significant number of these tumors metastasize. We describe the clinicopathologic features of 7 new cases of LGFMS including one case of dedifferentiation in a recurrence.

7 cases obtained from the surgical files of the CHUQ, L'Hôtel-Dieu de Québec or from the consultation files were studied.

The patients' age (5 male and 2 female) ranged from 16 to 55 years old. The tumors were located in the thigh (4), the deltoid muscle (2) and in the mesentery (1). They measured from 2.3 to 15 cm (greatest diameter). Histologically, the tumors were characteristically more fibrous than myxoid. Tumors cells were bland, oval to spindle shape, and arranged, at least in part, in a storiform or whorled growth pattern. Cellularity was most prominent in fibrous areas and there were small, sometimes curvilinear vessels in the myxoid areas. Mitotic figures were uncommon. Follow-up of patients ranged from 3 (1/2) months to 22 years. Four patients showed recurrence. One of them demonstrated an area of dedifferentiation into a high grade pleomorphic sarcoma, malignant fibrous histiocytoma (MFH) type. The same patient also had a pulmonary metastasis.

Differential diagnosis of LGFMS should include intramuscular myxoma, myxoid liposarcoma, myxoid variant of dermatofibrosarcoma protuberans and low grade myxofibrosarcoma. The chimeric FUS/CREB3L2 gene seems to be specific for LGFMS and its expression in the t(7;16)(q33p11) is a useful tool for the differential diagnosis. We report a unique case with areas of high grade sarcoma, MFH type, and areas similar to sclerosing epithelioid fibrosarcoma.