MMP9 and gastric cancer: The higher expression levels of both CXCL8 and MMP9 in a gastric cancer sample were also confirmed in the TCGA data when compared with a normal sample (Figure 3) analyzed with GEPIA (Tang et al., 2017), and it was further found that the correlation between CXCL8 and MMP9 expressions was R = 0.49 (Figure 4, p = 0).