Tumor markers are proteins found in blood the levels of which correlates with the type and activity of some cancers. Some tumor markers are antigens, others are enzymes. Some common tumor markers are: carcinoembryonic antigen (CEA) prostate-specific antigen (PSA) prostatic acid phosphatase (PAP) CA 125 alpha-fetoprotein (AFP) human chorionic gonadotropin (HCG) lactate dehydrogenase (LDH) neuron-specific enolase carbohydrate antigen 15-3 carbohydrate cntigen 19-4 cathepsin D