RAF1 Gene Fusions as a Possible Driver Mechanism in Rare BAP1-Inactivated Melanocytic Tumors: A Report of 2 Cases

Abstract: BRCA1-associated protein ( BAP1 )-inactivated melanocytic tumor (BIMT) is a group of epithelioid melanocytic neoplasms characterized by the loss of function of BAP1 , a tumor suppressor gene located on chromosome 3p21. They occur sporadically or in the setting of an autosomal-dominant cancer susceptibility syndrome that predisposes to the development of different internal malignancies. Most of these cutaneous lesions are associated with a BRAF -mutated melanocytic nevus and therefore are included in the group of combined nevi in the last WHO classification of skin tumors. Apart from a BRAF mutation, an NRAS mutation has been reported in rare cases, whereas in some lesions no driver mutation has been detected. Here, we report 2 cases of BIMTs with a BAP1 mutation and a RAF1 fusion. Both lesions proved to be BRAF and NRAS wild type and were associated with a conventional melanocytic nevus with dysplastic junctional features. We suggest that RAF1 fusions can represent an underlying driver genetic event in these cases. Our study extends the morphological and molecular spectrum in BIMTs.