Kinetics of Serum Tumor Marker Concentrations and Usefulness in Clinical Monitoring‪.‬

Only a few markers have been instrumental in the diagnosis of cancer; they include [alpha]-fetoprotein (AFP), (9) human chorionic gonadotropin (hCG), and calcitonin. Although the concentration of an isolated tumor marker before any treatment may have a prognostic value, they are not widely used in comparison to conventional prognostic factors. In contrast, tumor markers play a critical role in the monitoring of patients. However, recourse to tumor markers as a yardstick of treatment or to signal the emergence of a recurrence or a metastasis has been based only on a succession of values with no regard for knowledge of the exponential nature of tumor growth, which is a theoretical and practical basis of cancer therapy. In an economy-conscious environment in which cost-effective medicine is an overriding concern, physicians treating cancer patients need convenient, efficient methods to rapidly evaluate response to therapy and to offer alternative treatment when appropriate (1-4). A challenging approach to rapid evaluation of clinical response and monitoring is the determination of tumor marker half-life ([t.sub.1/2]) and tumor marker doubling time (DT), kinetic parameters associated with changes in marker concentrations. The [t.sub.1/2] is calculated according to the formula dt/log([tm.sub.1]/[tm.sub.2]), where [tm.sub.1] and [tm.sub.2] are the tumor marker values at times 1 and 2, respectively, and dt the interval between the two dates. The DT is determined according to the interval required to double the serum concentration. This report reviews the interest of determining kinetic parameters of the tumor markers that are the most relevant for the monitoring of patients. The main characteristics of prostate-specific antigen (PSA), hCG, AFP, carcinoembryonic antigen (CEA), cancer antigen (CA)125, and CA 15-3, are presented in Table 1. Dynamic Aspects of Tumor Markers