MYXOFIBROSARCOMA - CLINICOPATHOLOGICAL ANALYSIS OF 75 CASES WITH EMPHASIS ON THE LOW-GRADE VARIANT

Myxofibrosarsoma is one of the most common sarcomas in the extremities of elderly patients. We analysed the clinicopathologic features in a series of 75 patients. All patients were adults (range, 22-91 years; m edian, 66 years) with an approximately equal incidence in men and wome n. Thirty-five tumors arose in the lower and 25 in the upper extremiti es, nine on the trunk, two each in the retroperitoneum and the head an d neck region, and one each in the pelvis and penis. Forty-eight cases (69.5%) were located in dermal or subcutaneous tissues. Distinctive h istologic features included the following: a commonly nodular growth p attern; a myxoid matrix containing elongated, curvilinear capillaries; and fusiform, round or stellate tumor cells with indistinct cell marg ins, slightly eosinophilic cytoplasm, and hyperchromatic atypical nucl ei. These lesions varied from a hypocellular, mainly myxoid, and purel y spindle-cell appearance (low-grade neoplasms) to high-grade, pleomor phic (malignant fibrous histiocytoma-like) lesions with multinucleated giant cells, high mitotic activity, and areas of necrosis. Immunohist ochemistry in 44 cases revealed only vimentin and occasional actin pos itivity. Ultrastructurally, tumor cells had a fibroblastic phenotype. DNA flow cytometry and proliferation analysis showed an association be tween aneuploidy and histologic grade. An average follow-up of 45 mont hs (range, 5-300 months) in 60 cases has revealed local recurrence in 33 cases (54%). Thirteen patients developed metastases, and 13 tumor-r elated deaths occurred. A short interval to first local recurrence was associated with poor clinical outcome. The rate of local recurrence w as independent of histologic grade, but only intermediate and high-gra de neoplasms metastasized. The depth of the primary lesion did not inf luence the incidence of local recurrence. However, in deep-seated neop lasms, the incidence of metastases was higher and the percentage of tu mor-related deaths was twice as high as in superficially located lesio ns, reflecting the fact that deep-seated lesions tended to be higher-g rade, larger tumors. Myxofibrosarcoma tends to become progressively hi gher grade in recurrences, as demonstrated in five cases in our series . The poorly recognized low-grade myxofibrosarcoma is emphasized, as p roper diagnosis and treatment and scrupulous follow-up are mandatory t o avoid local recurrence and gradual tumor progression to a higher-gra de neoplasm that may then metastasize.