EMA+ cells in dermatofibrosarcoma protuberans. A study of 11 tumors suggesting perineurial cell differentiation

Expression of epithelial membrane antigen (EMA) was found in 11 of 57 (19%) cases of dermatofibrosarcoma protuberans (DFSP). These tumors with EMA+ cells showed the following histological features: classical storiform pattern in all 11 cases, myxoid areas in three cases, Bednar tumor pattern in one case, and fibrosarcoma-like areas in one case. The EMA+ cells had a tendency to occur in moderately cellular and collagen-rich areas with parallel cell arrangement (4 cases) and in perivascular areas (3 cases). In such parts, a nuclear palisading and a wavy appearance of the nuclei were seen focally. One tumor contained perineurioma-like areas with whorled cell arrangement and EMA+ cells. The EMA+ cells were also found in ordinary storiform areas (6 cases), but here they were isolated and scarce. In two cases, the EMA+ cells were juxtaneural; therefore their origin from a sheath of preexisting nerves can not be excluded. Expression of EMA may reflect true perineurial cell differentiation in DFSP, as suggested previously in several ultrastructural and cytogenetic studies. The knowledge of occasional EMA positivity in DFSP is needed for a differential diagnosis between DFSP and other EMA+ soft tissue lesions.