To unveil the roots of serum tumor markers, we selected AFP, CEA (encoded by CEACAM5)19 and PSA (encoded by KLK3)20, which are widely used in hepatocellular carcinoma (LIHC), colorectal cancer (COAD, READ) and prostate cancer (PRAD), respectively. This evidence concerns the gene KLK3 and colon adenocarcinoma.