(Also called AFP.) The liver of the fetus usually produces this plasma protein. Alpha-fetoprotein levels in the blood typically go down after birth, and by year one, the serum is virtually undetectable. The protein can reappear in the adult during some pathological stages. The alpha-fetoprotein level in the blood can be used as early detection for some cancer forms, most prominently hepatocellular carcinoma. It is elevated in liver tumors, hepatoblastoma, hemangioendothelioma, and hepatocellular carcinoma. The level produced by liver tumors allows for the response of the treatment of the tumors to be monitored.