Topalian et al. observed an objective response (either CR or PR) in 36% of patients with PD-L1–positive tumors and in none with PD-L1–negative tumors [25], while a systematic review of 20 trials in metastatic melanoma, NSCLC, and RCC patients receiving anti–PD-1/PD-L1 antibodies showed a significant decrease (53%) in the risk of mortality in patients with malignant melanoma positive for PD-L1, but no such response relationship was observed for NSCLC or RCC [26]. Here, PDCD1 is linked to metastatic melanoma.