BTLA and esophageal squamous cell carcinoma: A total of 721 ESCC patients and 1208 matched non‐cancer controls were included in this research, and four tagging BTLA polymorphisms (rs2171513 G > A, rs3112270 A > G, rs1982809 G > A, and rs16859629 T > C) were selected and genotyped using SNPscanTM Assays.