Which antigens are referred to as oncofetal antigens?

• A. AFP and CEA
• B. hCG and AFP
• C. CA 19-9 and CEA
• D. CA 125 and CA 27.29

Answer: (A)

Oncofetal antigens are proteins that are present in fetal tissues and later re-expressed by certain cancers, making them useful tumor markers. Alpha-fetoprotein is produced by the fetal liver and yolk sac; after birth it remains very low, but it rises in hepatocellular carcinoma and some germ cell tumors. Carcinoembryonic antigen is formed in the fetal gut; in adults it’s usually low but can be elevated in colorectal cancer and other malignancies. Because both AFP and CEA fit this pattern of fetal expression and cancer re-expression, they are classic oncofetal antigens.

Other options mix markers that are not classically oncofetal. hCG is a pregnancy hormone and a tumor marker in certain germ cell tumors, but it’s not grouped with oncofetal antigens. CA 19-9, CA 125, and CA 27.29 are cancer-associated markers linked to specific cancers, not fetal antigens re-expressed in cancer.