Kinetics of serum tumor marker concentrations and usefulness in clinical monitoring.

Only a few markers have been instrumental in the diagnosis of cancer. In contrast, tumor markers play a critical role in the monitoring of patients. The patient's clinical status and response to treatment can be evaluated rapidly using the tumor marker half-life (t(1/2)) and the tumor marker doubling time (DT). This report reviews the interest of determining these kinetic parameters for prostate-specific antigen, human chorionic gonadotropin, alpha-fetoprotein, carcinoembryonic antigen, cancer antigen (CA) 125, and CA 15-3. A rise in tumor markers (DT) is a yardstick with which benign diseases can be distinguished from metastatic disease, and the DT can be used to assess the efficacy of treatments. A decline in the tumor marker concentration (t(1/2)) is a predictor of possible residual disease if the timing of blood sampling is soon after therapy. The discrepancies in results obtained by different groups may be attributable to the multiplicity of immunoassays, the intrinsic characteristics of each marker (e.g., antigen specificity, molecular heterogeneity, and associated forms), individual factors (e.g., nonspecific increases and renal and hepatic diseases) and methods used to calculate kinetics (e.g., exponential models and timing of blood sampling). This kinetic approach could be of interest to optimize patient management.