[Clinical usefulness of circulating tumor markers]

There are many molecular tumor markers for diagnosing and monitoring cancer patients. Especially, quantitative assay for serum levels of tumor markers; such as AFP, CEA, PSA, hCG, CA 19-9 and CA 125, are frequently used in daily practice because of their relative specificities and usefulness to the common cancers. Though not suitable for early diagnosis, but they are used in monitoring patients with advanced caner, especially after treatments. Two of them, AFP and PSA, are also used in the screening and monitoring of high-risk groups, namely patients with chronic viral hepatitis and old male, who are the high risk for hepatoma and proste cancer respectively. Problems in using serum markers are; relatively low specificity and low sensitivity to cancer, confusing naming for similar markers that recognize almost the same molecule of cancer. Users must understand that CA 19-9, CA 50, KM-O 1 and SPAN-1 are in the same sialylated Lewis A group, and CA 125, CA 130 and CA 602; in the mucin antigen group, and STN, CA 54/61 and CA 72-4; in the sialyl Tn antigen group. Combination of two or more markers may inform us the biological characteristics of the cancer. For example, a germ-cell tumors may produce hCG and placental marker. That is of the choriocarcinoma type. Those with hCG and fetal antigens are the ordinal type of germ cell tumors, and those with AFP, CEA and cytokeratin are teratoma, and those with LDH and ALP only but negative for hCG and AFP must be seminoma. For the bronchial and alveolar carcinomas, CEA, SCC, NSE and cytokeratin 19 fragments are useful. Combination may be difficult for beginners but once understood, it will be an art in clinical oncology.