Ulcerated CRTC1::TRIM11 cutaneous tumor with metastases

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.

Update on cutaneous mesenchymal tumors in the 5th edition of WHO classification of skin tumors with an emphasis on new fusion-associated neoplasms

The section on mesenchymal tumors in the 5th edition of WHO classification of skin tumors has undergone several changes, the most important of which is the inclusion of newly identified tumor entities, which will be the main focus of this review article. These specifically include three novel cutaneous mesenchymal tumors with melanocytic differentiation, and rearrangements of the CRTC1::TRIM11, ACTIN::MITF, and MITF::CREM genes as well as EWSR1::SMAD3-rearranged fibroblastic tumors, superficial CD34-positive fibroblastic tumors, and NTRK-rearranged spindle cell neoplasms. Some of the other most important changes will be briefly mentioned as well.