CD274 and gastroesophageal junction adenocarcinoma: During carcinogenesis, the tumor cells express PD-L1, which causes a reduction of immunogenicity; thus, it is not recognized by the immune system and escapes the immune attack [6]. PD-L1 positivity is seen in cases with advanced pathological features, which suggests its role in the tumorigenesis of gastric and gastroesophageal junction adenocarcinoma [7].