CD274 and esophageal squamous cell carcinoma: Among the five identified studies in advanced ESCC, four reported survival benefit that correlated with PD-L1 expression level whereby PD-L1-positive (≥1%) patients achieved greater benefit than PD-L1-negative (<1%) patients, and patients with intermediate/high PD-L1 (≥10%) benefited more than those with low/no PD-L1 expression (<10%).