Alpha-fetoprotein (AFP) is a major plasma protein expressed at high concentrations during fetal development; however, concentrations decrease drastically after birth. When hepatocytes regenerate or proliferate, as seen in liver disease or cancer, AFP expression is activated again, and concentrations increase. Increased serum AFP levels have been used as a clinical biomarker for liver cancer detection, specifically hepatocellular carcinoma (HCC) and germ cell (nonseminoma) carcinoma, since the 1980s. Serum AFP can be fractionated in three forms (AFP-L1, AFP-L2, AFP-L3), with the AFP-L3 fraction being most important in the diagnosis and prognosis of hepatocellular carcinoma.