PDCD1 and esophageal squamous cell carcinoma: The NCT04140500 and NCT04785820 studies aimed to explore the efficacy and safety of anti-LAG-3 and anti-PD-1 combination therapy, while the NCT03708328 and NCT04785820 are designed to investigate the efficacy and safety of anti-TIM-3 and anti-PD-1 combination therapy for patients with ESCC.