Malignant tumors have been known for many years to release proteins or polypeptides into the circulation (for review,seeref.1 ). Some of these molecules have biological activity, resulting in endocrinologic manifestations of malignancy referred to as paraneoplastic syndromes. In contrast, others do not cause clinical symptoms, but rather serve as markers to aid in diagnosis, monitoring of tumor response, and selection of patients for adjuvant treatment. In this latter category are prostate-specific antigen (PSA), carcinoembryonic antigen (CEA), β-human chorionic gonadotropin (β-HCG), and CA-125. Tumor markers may be specific for certain tumors, such as PSA for prostate cancer, or more generally expressed, such as CEA.
