CD274 and esophageal squamous cell carcinoma: The results of phase Ib clinical trial KEYNOTE-028 showed that pembrolizumab demonstrated durable antitumor activity and manageable toxicity in patients with heavily pretreated, PD-L1-positive advanced ESCC [objective response rate (ORR): 30% (95% CI, 13%-53%); DoR: 15 months (range, 6-26 months); OS: 7.0 months (95% CI, 4.3-17.7 months); PFS: 1.8 months (95% CI, 1.7-2.9 months)] (185).