Epithelioid variant of myxofibrosarcoma: expanding the clinicomorphologic spectrum of myxofibrosarcoma in a series of 17 cases.

Myxofibrosarcoma (MFS) is one of the most common soft tissue sarcomas of elderly patients and has a predilection for the limbs. Herein, we report a previously undescribed variant of MFS showing epithelioid morphology. Seventeen cases diagnosed as epithelioid MFS were retrieved from the authors' files from among 570 cases of MFS. Hematoxylin and eosin-stained sections were reexamined and immunostains for pan-keratin (15 cases), S-100 protein (15), desmin (15), and alpha-smooth muscle actin (13) were performed. Nine patients were men and 8 were women (age range 43 to 89 y; median 63.5). Fifteen patients presented with a mass, and in 2 of these there was also pain. Duration of symptoms varied from 1 to 24 months (median 3). Tumor size ranged from 2 to 15 cm (median 6.75). In 10 cases, the tumor was located in subcutaneous tissue and in 6 cases it was subfascial. The majority of the tumors were located on the limbs (8 lower extremities and 6 upper extremities) followed by neck (1), scalp (1), and trunk (1). Follow-up was available for 14 patients (range 2 to 240 mo; median 16). Twelve patients were treated by surgery followed by chemotherapy and/or radiation (8 cases). One patient received chemotherapy after an incisional biopsy and 1 patient was treated by surgery alone. Ten patients (71.4%) developed local recurrences. Seven patients (50%) developed metastases to lungs or retroperitoneum. Five patients (35.7%) have died of disease so far. Two patients were lost to follow-up. Morphologically, 14 cases were high grade, 2 were intermediate, and 1 was low grade. Tumors were characterized by a multinodular, infiltrating growth pattern with alternation of hypercellular and hypocellular myxoid areas; the latter showed prominent curvilinear vessels. Neoplastic cells were arranged singly and in small clusters in the myxoid areas or formed sheets in the hypercellular areas, where they showed epithelioid morphology with round nuclei, vesicular chromatin, prominent nucleoli, and moderate amounts of eosinophilic cytoplasm. The epithelioid areas were generally multifocal with admixed areas of conventional MFS. Immunostains were negative for all markers studied. Differential diagnosis included carcinoma, melanoma, myoepithelial carcinoma, pleomorphic liposarcoma, and pleomorphic rhabdomyosarcoma. In conclusion, epithelioid MFS is a rare variant of MFS, accounting for <3% of MFS in consultation material. Its natural history seems more aggressive than usual high-grade MFS, with approximately 70% local recurrence and 50% metastases, even within a relatively short follow-up period.