Alpha-fetoprotein (AFP) is a glycoprotein that is normally expressed in fetal liver and yolk sac endoderm. It can be used to mark hepatocellular carcinoma and a variety of germ cell tumors, such as yolk sac tumors of testis and ovaries. In the diagnosis of hepatocellular carcinoma, AFP has low sensitivity but high specificity, so it can be used in combination with other antibodies in the diagnosis of hepatocellular carcinoma.