Single-cell transcriptomic landscape deciphers intratumoral heterogeneity and subtypes of acral and mucosal melanoma.

Purpose: To identify the specific intratumoral and microenvironmental heterogeneity of acral (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 samples (28 AM, 11 MM, and 3 non-acral cutaneous melanoma [CM]), supplemented by in vitro and in vivo validation. Tumor and stromal cells were profiled using scRNA-seq, 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 (EMT) potential. MM displayed elevated neutrophil infiltration and CXCL3⁺ tumor-associated macrophages, while AM was enriched with PI16⁺ cancer-associated fibroblasts (CAFs) promoting tumor proliferation. Molecular classification revealed MM subtypes: an antigen-presenting subtype linked to favorable outcomes and a proliferative subtype associated with recurrence. TIGIT⁺ Treg cells were enriched in AM, suggesting targeted inhibition potential. Genomic analysis connected BRAF/NRAS mutations to ALDOA⁺ stem-like tumor cells and identified PTGDS as a therapeutic target in triple-WT 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, CXCL3⁺ macrophages in MM) and propose a framework for precision therapies, biomarker-driven trials, and risk stratification to improve outcomes in these aggressive melanomas.