To explore a possible relationship between the expression of PTGS2 and CA9 in colon carcinoma and head and neck carcinoma, we used correlation analysis in GEPIA2 which showed no correlation between the expression of these two genes in COAD and HNSC datasets as the value of correlation coefficients was around 0 (0.062 and -0.018, respectively). Here, CA9 is linked to head and neck carcinoma.