PTGER4 and gastric cancer: PUD risk alleles resulted in increased levels of EFNA1 and reduced levels of PTGER4, whereas GC risk alleles were associated with a decreased level of EFNA1 and an increased level of PTGER4. This suggested that the risk alleles of variants at EFNA1 and PTGER4 for GC (nonrisk alleles for PUD) potentially benefited peptic ulcer healing while imposing an increased risk for GC through upregulated cell proliferation and angiogenesis.