Markers produced by cancers include enzymes and isoenzymes, hormones, oncofetal antigens, carbohydrate epitopes recognized by monoclonal antibodies, receptors, and oncogene products.Enzymes were of the first groups of tumor markers identified. Their elevated activities were used to indicate the presence of cancer.Hormones as tumor markers were used for the detection and monitoring of cancer.Oncofetal antigens were discovered using conventional antisera...