INTERPRETATION OF RESULTS FOR TUMOR-MARKERS ON THE BASIS OF ANALYTICAL IMPRECISION AND BIOLOGICAL VARIATION

Interpretation of results for CA 15.3, carcinoembryonic antigen (CEA), and tissue polypeptide antigen (TPA) during breast cancer monitoring requires data on intra- (CV(P)) and inter- (CV(G)) individual biologic al variation, analytical imprecision (CV(A)), and indices of individua lity. The average CV(P) and CV(G) obtained from 22 healthy women were, respectively, 6.2% and 62.9% (CA 15.3), 9.3% and 86.8% (CEA), and 28. 3% and 133% (TPA). The indices of individuality were all < 0.6: 0.2 (C A 15.3), 0.15 (CEA), and 0.2 (TPA). CV(A) depended on the concentratio n of the analytes. CV(P) and CV(A) determine what constitutes a signif icant difference between sequential results. Assuming a CV(A) of 11.2% (CA 15.3), 9.5% (CEA), or 11.9% (TPA), results must differ by 30%, 31 %, or 72%, respectively, for P less-than-or-equal-to 0.05. We found th at CV(P) and CV(A) contribute considerably to the variation during bre ast cancer monitoring. Consequently, both CV(P) and CV(A) should be co nsidered in criteria for marker evaluation. Because of low indices of individuality, conventional cutoff limits are inappropriate both for i nitial identification and for follow-up of breast cancer.