Comprehensive genomic and immune profiling of non-V600 BRAF-mutated melanomas: Implications for therapeutic strategies beyond BRAF/MEK inhibitors.

Abstract

e21544 Background: The development of targeted therapies ( BRAF plus MEK inhibitors) and immune checkpoint inhibitors (ICIs) has significantly improved the outcomes of patients with advanced melanoma, particularly those harboring BRAF V600 mutations (Class 1). However, melanomas with non-V600 BRAF mutations (classes 2 and 3) remain a subset where effective therapeutic options beyond ICIs are lacking. In this study, we investigated the distinct genomic and immune profile of non-V600 BRAF melanomas to further understand the mechanism of resistance to BRAF/MEK inhibitors and explore other pathways of potential therapeutic targets. Methods: A retrospective cohort of 175 melanoma samples was evaluated by comprehensive genomic and immune profiling, including tumor mutational burden (TMB) and the expression of 395 immune genes. Tumor specimens were classified as BRAFClass1, BRAFClass2, and BRAFClass3. TMB (high ≥10 Mut/Mb) was obtained by DNA sequencing. Gene expression signatures of tumor inflammation and cell proliferation were determined by targeted RNA-sequencing. We used chi-square and Wilcoxon rank-sum tests to determine the association of BRAF mutational status to genomic and immune correlates. Results: The median age of diagnosis was 69 years, with 57% of patients being male. A total of 152 (86.9%), 13 (7.4%), and 10 (5.7%) patients had BRAFClass1, BRAFClass2, and BRAFClass3 alterations, respectively. Genomic alterations in TP53, NF1, MET and ROS1 were more prevalent in BRAFClass2 and BRAFClass3 as opposed to BRAFClass1. BRAFClass2 and BRAFClass3 tumors combined had significantly higher tumor inflammation (median = 55.38; p < 0.05) compared to BRAFClass1 (median = 41.79) as well as higher TMB (median = 54.8; p < 0.001) compared to BRAFClass1 (median = 9.75). BRAFClass3 tumors showed significantly higher cellular proliferation (median = 47.5; p < 0.05) compared to BRAFClass1 (median = 33.5) and BRAFClass2 (median = 31.8) tumors, as well as higher TMB (median = 71.5; p < 0.01) compared to BRAFClass1 (median = 10.9). When looking at differentially expressed genes, CDK1 was upregulated in BRAFClass3 compared to BRAFClass1 and BRAFClass2, and IL12B was upregulated in BRAFClass2 compared to BRAFClass1. Conclusions: Our study showed that the non-Class 1 BRAF (V600E or K) mutated tumors have higher immune response suggesting a favorable response to ICIs. Additionally, we found that BRAFClass2 and BRAFClass3 tumors more commonly harbor alterations in NF1 and TP53, supporting the prior understanding that BRAF non-V600 tumors have a more aggressive clinical course. Comprehensive molecular analysis offers insight into the immunogenicity and distinct oncogenic drivers associated with unfavorable clinical outcomes, which could guide therapeutic development beyond BRAF and MEK inhibitors in BRAF non-V600 melanomas.