Notably, the PD-1.5 (rs2227981), PD-1.6 (rs10204525), and PD-1.9 (rs2227982) polymorphisms are associated with several cancers, including lung adenocarcinoma [16], cervical cancer [17], gastric cancer [18], and thyroid cancer [19]. This evidence concerns the gene PDCD1 and lung adenocarcinoma.