Single-Cell Transcriptomic Landscape Deciphers Intratumoral Heterogeneity and Subtypes of Acral and Mucosal Melanomas

Purpose: To identify the specific intratumoral and microenvironmental heterogeneity of acral melanoma (AM) and mucosal melanoma (MM), we aimed to delineate their distinct cellular compositions, evolutionary trajectories, and subtype-specific therapeutic strategies. Experimental Design: Single-cell transcriptomic and genomic landscapes were analyzed across 42 melanoma (28 AM, 11 MM, and 3 nonacral cutaneous melanoma) samples, supplemented by in vitro and in vivo validation. Tumor and stromal cells were profiled using single-cell RNA sequencing, whole-exome sequencing, and functional assays, including transwell migration, co-culture systems, and xenograft models. Results: Tumor cells exhibited divergent evolutionary routes, with MM dominated by MGP⁺/PCOLCE⁺ subpopulations showing high epithelial-to-mesenchymal transition potential. MM displayed elevated neutrophil infiltration and CXCL3⁺ tumor-associated macrophages, whereas AM was enriched with PI16⁺ cancerassociated fibroblasts promoting tumor proliferation. Molecular classification revealed MM subtypes: an antigen-presenting subtype linked to favorable outcomes and a proliferative subtype associated with recurrence. TIGIT⁺ regulatory T cells were enriched in AM, suggesting targeted inhibition potential. Genomic analysis connected BRAF/NRAS mutations to ALDOA⁺ stem-like tumor cells and identified prostaglandin D2 synthetase as a therapeutic target in triple–wild-type/melanomas. Conclusions: Our study provides a comprehensive comparison of AM and MM, uncovering subtype-specific stromal– immune interactions and molecular programs. The findings highlight actionable targets (e.g., TIGIT in AM and CXCL3⁺ macrophages in MM) and propose a framework for precision therapies, biomarker-driven trials, and risk stratification to improve outcomes in these aggressive melanomas.