PDCD1 and esophageal squamous cell carcinoma: Similarly, several investigations were not able to find any association between PD-1 rs2227982 variant and susceptibility or protection to BC (Hua et al., 2011), esophageal cancer (ESCC) (Qiu et al., 2014) and non-small cell lung cancer (NSCLC) (Ma et al., 2015).