The Impact of Molecular Characteristics on the Efficacy of Frontline Immune Checkpoint Inhibitor Therapy in Patients with Metastatic Melanoma

Background: Metastatic melanoma in East Asian populations is enriched for acral and mucosal subtypes and harbors a distinct molecular landscape compared with Western cutaneous melanoma. However, data on the efficacy of first-line immune checkpoint inhibitor (ICI) therapy and on the impact of molecular characteristics on treatment effect in this population remain limited. We aimed to characterize the genomic landscape of an East Asian metastatic melanoma cohort and to evaluate the predictive values of molecular markers for first-line ICI therapy. Methods: This study included 135 patients with metastatic melanoma who received first-line ICI at Samsung Medical Center between January 2022 and December 2025. Of these, 108 with paired next-generation sequencing (NGS) data were included in the molecular analysis. Survival outcomes were estimated by the Kaplan–Meier method, and the prognostic value of molecular subtype was assessed using univariable and multivariable Cox proportional hazards models. Results: Mucosal melanoma was the most common primary site (58, 43.0%), followed by acral melanoma (31, 23.0%) and cutaneous melanoma (25, 18.5%); 4 (3.0%) had uveal melanoma and 17 (12.6%) had melanoma of other or unknown primary origin. The overall objective response rate to first-line ICI was 37.8% (51 of 135), and median progression-free survival (PFS) was 6.2 months (95% confidence interval [CI] 4.0–9.6). Using the hierarchical classification, 108 patients were classified into five molecular subtypes: BRAF-altered (n = 17, 15.7%), RAS-altered (n = 17, 15.7%), KIT-altered (n = 15, 13.9%), and NF1-altered (n = 7, 6.5%), and quadruple–wild-type (n = 52, 48.1%). TMB-high status (10.2%) showed no significant association with outcomes. Molecular subtype was significantly associated with PFS (log-rank p = 0.009). After multivariable adjustment, BRAF fusion (hazard ratio [HR] 5.05, 95% CI 1.70–14.98, p = 0.003) and KIT-altered status (HR 2.91, 95% CI 1.46–5.77, p = 0.002) emerged as independent adverse prognostic factors, whereas BRAF V600 single-nucleotide variants did not differ significantly from quadruple–wild-type. Conclusions: In this East Asian metastatic melanoma cohort, BRAF fusion and KIT alterations were independent adverse prognostic factors for first-line ICI. These findings suggest that BRAF fusion and KIT-altered tumors may represent distinct subgroups that warrant further investigation.