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. Here, KLK3 is linked to hepatocellular carcinoma.