STAT1 and esophageal squamous cell carcinoma: Recent studies have shown that PD-L1 expression in tumor cells, particularly in gastrointestinal malignancies such as oral squamous cell carcinoma, esophageal squamous cell carcinoma, gastric cancer, pancreatic cancer, liver cancer, and colorectal cancer, is regulated via the IFN-γ/STAT1 pathway, with IRF-1 acting as a key downstream mediator.