Gene fusions in melanocytic lesions: an updated comprehensive review

The scope of gene fusions in melanocytic neoplasms is broader than previously recognized, extending well beyond the Spitz-lineage neoplasms where kinase fusions involving ALK, ROS1, NTRK1/2/3, RET, MET, BRAF, and MAP3K8 define biologically and morphologically distinct tumors. Emerging studies demonstrate that a meaningful proportion of conventional non-Spitz lineage melanomas harbor oncogenic fusions. Such fusions may impact clinical behavior, histopathologic presentation and provide opportunities for targeted therapy. The World Health Organization classification of skin tumors, 5th edition, now incorporates fusion status into taxonomy and risk stratification, yet some important questions remain for further investigation: fusion-associated neoplasms can mimic non-melanocytic neoplasm; Spitz-type fusions appear in non-Spitz lesions; and melanocytic differentiation may occur in some other fusion-driven lesions. Broad-panel next-generation sequencing (including RNAseq), together with targeted fluorescence in situ hybridization and immunohistochemistry enhances detection of known and novel fusion partners. Early clinical evidence of TRK, ALK, and ROS1 inhibitor efficacy underscores the translational promise of fusion testing and opens avenues for personalized therapy. This review synthesizes current knowledge on the genomics, histopathology, diagnosis, and therapeutic implications of fusion-driven melanocytic neoplasms, highlighting consensus points and remaining controversies.