Clear cell tumor with melanocytic differentiation and MITF-CREM translocation: a novel entity similar to clear cell sarcoma.

The presence of melanocytic differentiation in tumors of non-melanocyte origin is uncommon and is typically associated with the overexpression of MITF, the master regulator of melanin synthesis, or another member of the MIT/TFE3 family. In clear cell sarcoma, the presence of either an EWSR1-ATF1 or EWSR1-CREB1 translocation-derived fusion protein is thought to drive melanocytic differentiation by directly stimulating the expression of MITF. Here, we describe a clear cell neoplasm with melanocytic differentiation that is characterized by a novel MITF-CREM gene fusion. CREM is the third member of the ATF1/CREB1/CREM family, and the nature of the MITF-CREM fusion appears analogous to the EWSR1-ATF1 and EWSR1-CREB1 fusions. Thus, this MITF-CREM-rearranged clear cell tumor represents a novel entity with morphologic, immunohistochemical, and molecular similarity to clear cell sarcoma.