PRSS8 and esophageal squamous cell carcinoma: To determine whether the reduction of PRSS8 in ESCC tissues and cell lines was caused by hypermethylation in PRSS8 promoter region, we used the methylation CpG island prediction software [22] and identified one CpG island in PRSS8 promoter region (−4238 to -4116) (Figure 3A).