NRAS mutation in melanoma: Association of codon-specific changes on patient outcomes.

e21545 Background: NRAS mutant melanoma is an aggressive subtype making up 20-30% of cutaneous melanoma cases without specific treatment options beyond immune checkpoint inhibition (ICI). Previous studies have suggested specific NRAS codon mutations are associated with unique signaling pathways. To test the hypothesis that NRAS codon mutations in cutaneous melanoma may drive a preferential response to ICI, we evaluated specific genetic subsets of NRAS mutant melanoma based on the Q61 and G12/G13 codons. Methods: Cutaneous melanoma samples (n = 4091) were analyzed by NGS at Caris Life Sciences. Samples were stratified by NRAS status and subdivided into NRAS Q61 , NRAS G12/13 , and NRAS-wildtype. PD-L1 expression was assessed using IHC (positive ≥ 1%). TMB-high was defined as ≥ 10 mutations/Mb. Transcriptomic signatures of MAPK pathway activation and T-cell signatures were calculated. Real-world overall survival (rwOS) information was obtained from insurance claims data, with Kaplan-Meier estimates calculated from time on ICI until last date of contact. Mann-Whitney U, Chi-square, and Fisher exact tests were applied as appropriate, with p-values adjusted for multiple comparisons. Results: Cutaneous melanoma samples were comprised of 22% NRAS Q61 (n = 902), 3.1% NRAS G12/13 (n = 125) and 74.8% NRAS WT (n = 3064), with the most common NRAS mutation being Q61R. Patients harboring NRAS G12/13 codon changes were associated with concurrent mutations in BRAF (21.0 vs 6.4%, p< 0.0001), NF1 (50.5% vs 8.7%, p< 0.0001), KIT (3.2% vs 0.2%, p< 0.001), ARID2 (22.1% vs 11.3%, p< 0.01), MAP2K1 (7.2% vs 2.6%, p = 0.022) compared to NRAS Q61 . NRAS G12/13 tumors were more frequently TMB-high compared to NRAS Q61 or NRAS WT (83.1% vs 62.1% vs 55.1%, p = 0.0001), but no difference was observed in the prevalence of dMMR/MSI-H or PD-L1 expression. Transcriptomic analysis showed that NRAS Q61 mutants had a significantly higher MPAS compared to NRAS G12/13 or NRAS WT cohorts (Median: 1.16 vs 0.67 vs 0.46, p = 0.0147), while T-cell-inflamed scores were significantly higher in NRAS WT compared to NRAS Q61 (Median: 4 vs -40, p = 0.00492) but not to NRAS G12/13 (Median: 4 vs -13.5, p = 0.674). No difference in rwOS was identified in NRAS G12/13 and NRAS Q61 melanoma treated with ICI (HR: 0.753, 95% CI: 0.43 – 1.31, p = 0.316). Conclusions: Patients with NRAS-mutated cutaneous melanoma exhibit codon-specific ( NRAS Q61 vs NRAS G12/13 ) signaling and prevalence of immunotherapy-related biomarkers. Our findings indicate that melanoma samples with NRAS G12/13 mutation tend to exhibit immune richness suggesting they could be viewed as a distinct group that might potentially benefit from immune therapies. This observation offers valuable insight into codon-specific tumor subsets, differential response to therapy, resistance mechanisms, and the potential development of combination therapies to enhance survival outcomes of patients with NRAS mutant melanoma.