Relevance of detection of RAF fusion transcripts in pan-negative melanoma in routine practice.

Abstract

Pan-negative melanomas account for 30% of melanomas. In case of immunotherapy failure, therapeutic options are limited. Oncogene fusions represent a target of interest in many solid cancers. In melanoma, the frequency of oncogene fusion is not well documented and not routinely investigated. We conducted a single-center retrospective study. The objective was to determine the frequency of oncogene fusion detected by RNA sequencing, in patients with advanced or metastatic pan-negative melanoma. In parallel, an extended molecular alteration search was performed using extended targeted next-generation sequencing. We identified 59 patients with advanced pan-negative melanoma between January 2021 and January 2023. It was a cutaneous melanoma in 71.1% of the cases, a mucous melanoma in 15.2% of the cases. We identified nine patients with a RAF fusion, including seven BRAF gene fusion and two RAF1 fusion. Of the other molecular alterations, NF1 mutation was the most frequent molecular alteration identified. Among the nine patients with RAF fusions, all the patients initially received treatment with anti-PD1 ± anti-CTLA4 immunotherapy. After immunotherapy failure, five patients benefited from second-line targeted therapy (two with BRAF and MEK inhibitors combination, three MEK inhibitors alone). The response rate was 20%. In a population of pan-negative melanoma, we detected 15.2% of RAF fusion. Fusion detection allowed the introduction of a second line of targeted therapy, in the absence of a validated therapeutic option in 55.5% of cases. This study suggests the relevance of detecting RAF fusion in a selected population.