PTGS2 and gastric cancer: Another group of biomarkers identified in this review have contradictory functions in cancer development, however, they are consistently overexpressed (COX2, CCL18, CXCL9, CXCL10, CXCL11), underexpressed (MUC5AC) or hypermethylated (TWIST-1) in H. pylori-infected children and adults with H. pylori-induced gastritis and/or GC.