CDKN1A and esophageal squamous cell carcinoma: When the p21 rs3176352 GG homozygote genotype was used as the reference group, the GC genotype was not associated with the risk for ESCC; the CC genotype was associated with a significantly increased risk for ESCC (CC vs. GG: adjusted OR = 1.61, 95% CI = 1.18–2.20, p = 0.0030).