MITF Pathway-Activated Cutaneous Neoplasms.

Over the past few years, several fusion genes have been reported in dermal-based tumors, resulting in the activation of the microphthalmia (MITF) signalling pathway and a melanocytic phenotype by immunohistochemistry. The best-studied example of these tumors is clear cell sarcoma, which rarely may present as a primary dermal tumor. These tumors are characterized by EWSR1 gene rearrangements, typically with ATF1 and less commonly CREB1. More recently reported cutaneous tumors show gene fusions involving CRTC1::TRIM11, ACTIN::MITF, MITF::CREM, and MED15::ATF1. While the entities in this tumor group share many features, they show subtle distinguishing features, including clinical presentation, histopathologic features, immunophenotype, and outcome. The following overview provides a detailed discussion of these rare tumors with emphasis on differentiating features and differential diagnosis.