Pedro Redondo

Background Multiple, large or giant congenital melanocytic nevi (CMN) are uncommon and affected patients can show progressive growth and thickening, associate neurocutaneous melanocytosis or develop melanoma. Current treatment modalities are mostly complex surgeries that frequently do not solve the disease and its risks completely. Thus, investigation on new treatment options for CMN and its complications must continue. MAPK pathway inhibitors are being investigated, also targeting PI3K‐AKT. Omipalisib (PI3K inhibitor, with no indications approved yet) has been studied for CMN in vitro and in mice with promising results. However, alpelisib, a PI3K inhibitor approved with an adequate safety profile for patients with severe manifestations of PROS (PIK3CA‐Related Overgrowth Spectrum), had not yet been tested for CMN. Objective To evaluate the effect of alpelisib in nevocytes of congenital melanocytic nevi. Methods Nevomelanocytic tissue samples of 10 patients were collected prospectively and, following a previously reported preclinical ex vivo model, explants were placed in organotypic culture for 5 days, with or without alpelisib. Consecutively, tissue sections were stained and using scanned images with Qupath and ImageJ softwares, representative regions from the dermis were analysed (using Wilcoxon test and Spearman's correlation). Results When comparing alpelisib‐treated explants with respect to control explants, we found a decrease in cell density ( p = 0.0273), in density of SOX10 + ‐cells ( p = 0.0391) and also in the % of S‐100 + area ( p = 0.0078), in alpelisib samples. The three markers showed a positive correlation ( p < 0.05). Conclusions This study provides first‐time evidence that alpelisib induces nevocyte reduction in CMN from patient‐derived explants, probably inducted by autophagy. Alpelisib is an approved drug with an adequate safety profile used in another mosaicism affecting PI3K (PROS). Further studies are needed to evaluate its efficacy in treating CMN and potentially, their complications, either with local or systemic administration, alone or in combination.