Alpha-Fetoprotein and its Receptor: More Than Oncofoetal Antigens

Oncofetal antigens are proteins which are typically present only during fetal development. However, they are also found in adults with certain kinds of cancer. These proteins are often measurable in blood of individuals with cancer and may be used to both diagnose and follow treatment of the tumors. Oncofetal antigens and clinical tumor markers include alpha-fetoprotein (AFP), carcinoembryonic antigen, beta-human chorionic gonadotropin, trophoblast glycoprotein precursor, immature laminin receptor protein, etc. AFP is produced by hepatocellular carcinoma and some germ cell tumors (its level increases during pregnancy in cases of spina bifida and other fetal malformations) 1. Carcinoembryonic antigen is produced by colon/rectum cancer, pancreas, breast, ovary or lung cancer. Beta-human chorionic gonadotropin is produced by germ cell tumors, testicular cancers and neuroendocrine islet cell tumors. Oncofetal antigens in the human body are synthesized for a different purpose, but they prove to be very convenient in detection, diagnosis, and management of some types of cancer or pregnancy defects. The most important two of the tumor markers are AFP and alpha-fetoprotein receptor (AFPR), which serve as nutrient delivery system to embryo and cancer cells. AFP originated from embryo yolk sac and liver can grab small molecules and essential nutrients from mothers' blood and deliver them through placenta specifically into the AFPR-positive cells in a shuttle manner 2. AFP was found only in few tumors (in liver, gonads and in cases of embryonic carcinoma). On the contrary, AFPR is present in over 80% of cancers (breast, lung, prostate, ovarian, stomach, etc.). Although it is not a “universal” tumor marker 3, AFPR has higher presence in cancer than any other oncofetal protein. That is why AFPR should be considered as the number 1 oncofetal protein. AFPR-positive embryo and cancer cells have definite benefits of targeted nutrient delivery.