Alpha Fetoprotein (AFP) is a major plasma protein produced by the fetal yolk sac and liver. Alpha-fetoprotein expression in adults is often associated with hepatoma or teratoma. However, hereditary persistance of alpha-fetoprotein may also be found in individuals with no obvious pathology. The level of alpha-fetoprotein in amniotic fluid is used to measure renal loss of protein to screen for spina bifida and anencephaly. In immunohistochemistry, antibodies to AFP have cytoplasmic positivity in hepatocellular carcinomas, embryonal carcinomas and yolk sac and other germ cell tumors. In normal tissue, AFP is positive in the placenta, shows cytoplasmic positivity in the liver, and can be found in extracellular secretions. References: Cancers (Basel). 2018 Apr; 10(4): 108, PMID: 29621151; Molecular and Clinical Oncology. 2013. 1.4: 593-598, DOI: 10.3892/mco.2013.119; International Journal of Hepatology. 2012. Vol 2012(893103), DOI:10.1155/2012/893103