Tumor markers: hormones, antigens, and enzymes in malignant disease.

Tumor markers (TM) represent a critical area of clinical investigation in cancer management. The mechanism of TM production and release are discussed for the three classes of TM: non-endocrine tumor produced hormones, tumor associated antigens, and tumor related enzymes. The concept of TM as a means of screening large patient populations for detection of early cancer has not been worthwhile, related in part to the uncommon occurrence of elevated levels of circulating TM, and in part to the fact that TM are generally abnormally elevated in patients with advanced and clinically detectable disease. Tumor markers as sequential monitors or quantitative measures of disease and response to therapy have similarly demonstrated limited utility, related to the heterogeneity of the tumors and to the lack of a precise quantitative relationship between circulating TM levels and tumor volume or mass.