However, the result of many studies revealed that PD-1 rs2227982 variant was a risk factor in several cancers including, leukemia(Ramzi et al., 2018), gastric cardia adenocarcinoma (Tang et al., 2017), esophageal squamous cell carcinoma (Zhou et al., 2016) and ovarian cancer (Tan et al., 2018). Here, PDCD1 is linked to esophageal squamous cell carcinoma.