PDCD1 and acral lentiginous melanoma: A systematic review of immune checkpoint inhibitors used in advanced ALM showed that the objective response rate of anti-CTLA-4 monotherapy was 11.4–25% (median OS > 7.16 months) compared to an objective response rate of 14–42% (median OS >14 months) for anti-PD-1 monotherapy; a single study investigating combination therapy showed an increased objective response rate of 42.9% [69].