In Vivo Melanoma Cell Morphology Reflects Molecular Signature and Tumor Aggressiveness

Melanoma is the deadliest type of skin cancer characterized by high cellular heterogeneity, which contributes to therapy resistance and unpredictable disease outcome. Recently, by correlating reflectance confocal microscopy morphology with histopathological type, we identified four distinct melanoma subtypes: dendritic cell, round cell, dermal nest, and combined-type melanomas. In this study, each reflectance confocal microscopy melanoma subtype expressed a specific biomolecular profile and biological behavior in vitro. Markers of tumor aggressiveness, including Ki-67, MERTK, nestin, and stemness markers were highest in the most invasive combined-type and dermal nest melanomas than in dendritic cell and round cell melanomas. This was also confirmed in multicellular tumor spheroids. Transcriptomic analysis showed modulation of cancer progression-associated genes from dendritic cell to combined-type melanomas. The switch from E- to N-cadherin expression proved the epithelial-to-mesenchymal transition from dendritic cell to combined-type subtypes. The dermal nest melanoma was predominantly located in the dermis, as also shown in skin reconstructs. It displayed a unique behavior and a molecular profile associated with a high degree of aggressiveness. Altogether, our results show that each reflectance confocal microscopy melanoma subtype has a distinct biological and gene expression profile related to tumor aggressiveness, confirming that reflectance confocal microscopy can be a dependable tool for in vivo detection of different types of melanoma and for early diagnostic screening.