Fusion-Associated Cutaneous Tumors with Melanocytic Differentiation.

Novel fusion-associated cutaneous dermal tumors with melanocytic differentiation have recently been described, some of which demonstrate morphologic similarities to cutaneous clear cell sarcoma (CCS), Spitz tumors, or other mesenchymal neoplasms of unclear histogenesis. All of these novel fusion-associated tumors demonstrate upregulation in the microphthalmia-associated transcription factor pathway, which likely accounts for their melanocytic differentiation. Despite similarities to clear cell sarcoma (CSS), they appear to behave in a relatively more indolent fashion. This article summarizes the clinical, histologic, immunophenotypic, and molecular features of these cutaneous tumors and compares them to other diagnoses in the histologic differential. The available outcome and treatment data are summarized.