One hundred and twenty-two patients in whom the CA 15-3 level showed either a decline (92 patients) or an acute surge followed by a decline (30 patients) after chemotherapy were included. The clinical characteristics between the two groups and the CA 15-3 kinetics using receiver operating characteristic curves were analyzed. Patients with a surge had a significantly higher risk of disease progression than patients without a surge (P = 0.004; odds ratio 2.62; 95% CI 1.45-4.72). The clinicopathologic characteristics were significantly different between the two groups with respect to the distribution of ER, PR, and HER2 status, relapse-free survival, and the severity and extent of the involved organs. For patients with a surge, a CA 15-3 slope threshold > -0.0038 was chosen with a sensitivity of 80.0% and a specificity of 80.4%. The area under the curve was 0.847 (95% CI 0.771-0.906; P = 0.0001). A significant correlation between PFS and CA 15-3 slope was shown with Cox-regression modeling (P = 0.036; hazard ratio [HR], 2.1; 95% CI 1.01-4.14).These kinetics may serve as a good predictive marker of treatment response and response duration.