CA 15-3 is a tumour marker that is frequently indicated and examined, particularly as part of breast cancer treatment. In our study we evaluate the diagnostic effectivenes of the examination and also the analytical response of eight routinely employed immunoassay sets for the determination of CA 15-3 in serum: six closed automated systems (AxSYM, Centaur, ECi Vitros, Elecsys 2010, Immulite 2000 and Kryptor), and two IRMA kits (ELSA CIS and IRMA-mat Byk-Sangtec). Low incidence of CA 15-3 in early (non-metastatic) breast cancer does not guarantee a sufficient sensitivity of this method for the preclinical diagnosis of tumour recurrence. Unfortunately, currently available treatment for recurrent breast cancer is not satisfactorily effective; thus early treatment of suspected recurrence based on the elevation of the tumour markers has not been proved to be of practical value. On the other hand, multivariate analysis demonstrated that the pre- and postoperative values of CA 15-3 are independent predictors of survival and disease-free interval.Patients with CA 15-3 < 30 kU/l at the time of the first recurrence have a longer survival time than patients with CA 15-3 > 30 kU/l. Using all analytical systems, we have measured identical groups of clinical samples. Even though the cut-off values differ among various systems, no similar clinical efficacy appears to be attained. In the region of cut-off values, the highest specificity that was set as standard was found for AxSYM analyser, while the sensitivity was highest for Elecsys 2010. Data from Bland-Altman differential plots suggest the presence of significant individual differences between individual samples, mainly in the region of high concentrations of CA 15-3. The parameters of Passing-Bablok regression show significant systematic differences among some of the analytical systems as well as an increase of the differences with increasing CA 15-3 concentrations. The effect of the combination of antibodies used on the extent of differences between results obtained with individual systems is more obvious than the effect of the matrix of analysed materials.

        Klíčová slova: CA 15-3 immunoassays, effectiveness, comparability, heterogeneity.