PDCD1 and esophageal squamous cell carcinoma: Meanwhile, due to few studies on esophageal cancer, it remains controversial about the prognostic and predictive value of PD-L1 expression in ESCC, as some studies associate high PD-L1 expression with poor differentiation of tumor and poor prognosis, while others postulate better response to PD-1/PD-L1 blockade with high PD-L1 expression.