Pleomorphic dermal sarcoma: adverse histologic features predict aggressive behavior and allow distinction from atypical fibroxanthoma.

The behavior of atypical fibroxanthoma is benign, if strict diagnostic criteria are applied. Tumors with similar pathologic features but deep subcutaneous invasion, necrosis, and/or lymphovascular or perineural invasion are thought to be associated with adverse outcome and are better regarded as pleomorphic dermal sarcoma or undifferentiated pleomorphic sarcoma of skin. This tumor group is not well documented in the literature, and its characteristics are only poorly defined. To study the clinical and pathologic spectrum more comprehensively, we retrieved 32 pleomorphic dermal sarcomas from our departmental files. The tumors were large (median: 25 mm) and exclusively presented on sun-damaged skin with a strong predilection for the head. Typically, elderly men were affected (median age: 81 y). Histologically, these often ulcerated tumors were poorly marginated, asymmetrical, and deeply invasive into deep subcutaneous, muscular, and/or fascial tissues. The tumors were cellular and composed of pleomorphic epithelioid cells, atypical spindle cells, and multinucleated tumor giant cells in varying proportions. Mitotic count was brisk and often atypical. Tumor necrosis was observed in 53%, lymphovascular invasion in 26%, and perineural infiltration in 29%. The majority of tumors showed a predominance of atypical spindle cells in a fascicular arrangement. A sheet-like growth of pleomorphic epithelioid cells or mixed spindle and epithelioid cell features were less frequently observed. Myxoid and keloidal change, a desmoplastic stromal response, pseudoangiomatous and storiform growth patterns, and admixed osteoclast-like giant cells were additional morphologic features in some cases. No immunoreactivity was noted for multiple cytokeratins, S100, HMB-45, desmin, and CD34. Smooth muscle actin was expressed in 70%, CD31 in 48%, epithelial membrane antigen in 16%, Melan A in 6%, and p63 in 1 case. CD10 was expressed in all cases stained. Follow-up (available for 29 patients; median: 24 mo) showed local recurrence in 28% and a metastatic rate of 10%, mainly in the skin. Progressive metastatic disease was observed in 2 patients. Remission was achieved in 1 patient using systemic chemotherapy. The second patient died in the setting of advanced-stage non-Hodgkin lymphoma. No disease-related mortality was noted. Our data underscore the importance of recognizing adverse histologic features in tumors otherwise resembling atypical fibroxanthoma. Deep subcutaneous invasion, tumor necrosis, and perineural and/or lymphovascular invasion confers at least low-grade malignant potential.