FOXP3 and melanoma: Comparison between the response groups showed that both ICI-resistant and non-resistant AYA melanomas harbored higher densities of FOXP3+ Tregs compared to resistant (median = 72.8 and 122 vs 9.38 cells/mm2, P = 0.0006 and 0.001) and non-resistant (median = 15.1 cells/mm2, P = 0.0048 and 0.0069) adult melanomas (Supplementary Fig. 2c).