CD274 and esophageal squamous cell carcinoma: In 2021, KEYNOTE-590, a randomized, placebo-controlled, phase 3 study, revealed that pembrolizumab + chemotherapy was superior to placebo + chemotherapy in terms of the OS in all randomized patients regardless of their CPS (12.4 months vs. 9.8 months, P < 0.001) and in patients with ESCC (P = 0.0006), PD-L1CPS ≥ 10 (P < 0.0001), and ESCC PD-L1 ≥ 10 (P < 0.0001) [13].