FOXP3 and neoplasm: We observed that the majority of Tregs (CD3+FOXP3+) in ICI-resistant AYA melanomas were localized in the stromal side of the tumor invasive margin (peritumor region; Fig. 3a), as shown by the significantly higher peritumoral Treg cell density compared to the intratumoral (Fig. 3b; median = 99.4 vs 17.3 cells/mm2, P = 0.0008).