Malignant melanoma (MM) is the deadliest type of skin cancer due to its aggressiveness and resistance to current therapies. Reflectance confocal microscopy (RCM) analyses features of the tumors at nearly histological resolution. RCM allows the identification of four MM subtypes: dendritic-cell (DC), round cell (RN), dermal-nest (DN) and combined-type (CT). The aim of this project was to study the biological behaviour of MM RCM-subtypes. 100 MM were evaluated by RCM and characterized by clinical, dermoscopic and histopatological analyses. DC and RC melanoma were generally Radial Growth Phase in stage I and II, while CT and DN were Vertical Growth Phase in stage III and IV. Ki67, as shown by immunohistochemistry, was significantly more expressed in epidermis in DC and RC (p<0.01). On the contrary, this marker was more expressed in the dermis in DN, indicating a greater invasive ability of this tumor type (p<0.01). Nestin expression increased from DC to CT (p<0.01), correlating with an increase in tumor aggressiveness. The expression of CD271 increased from DC to RC (p<0.01) and decreased from RC to CT (0.01<p<0.05). This correlates with our previously published concept that CD271 has a “switch on-off” function in melanoma progression. Co-expression of BMF and BRAFv660E was observed in CT, while inversely correlated in DC, RC and DN (p<0.01). Nestin and Sox2 were highly co-expressed in CT and DN, indicating an increase in aggressiveness from DC to CT-DN (p<0.01). SOX2 was inversely correlated with CD271 in all RCM-subtypes (p<0.01). Finally, RNA extracted from paraffin-embedded melanoma tissues were analysed for the expression of 770 genes by NanoString technology. This analysis revealed significant differences in the expression of genes involved in chemotaxis, inflammation, cell-cell adhesion, cell motility and angiogenesis. Taken together, these results show a progressive aggressiveness from DC to CT MM subtypes, while DN seems to have a unique behaviour.

Aggressiveness of melanoma subtypes selected by reflectance confocal microscopy