Background: Metronomic chemotherapy (MCT) with cyclophosphamide (Cy) and celecoxib (Cel) has therapeutic efficacy and low toxicity profile in advanced breast cancer patients (ABCP), but no reliable biomarkers of response have been found yet that allow patient selection for treatment. AIM: To investigate the potential role as biomarkers of pro- and antiangiogenic parameters and evaluate their response in ABCP receiving metronomic Cy 50 mg p.o./day + Cel 400 mg p.o./day. Materials and Methods: Serum levels of vascular endothelial growth factor-C (VEGF-C), soluble VEGF receptors 2 and 3 (sVEGFR-2, sVEGFR-3), were measured at different time points in 13/15 patients included in a phase II trial of MCT with Cy+Cel. Results: Serum levels of sVEGFR-2 and sVEGFR-3 increased significantly during treatment (P = 0.0392; P = 0.0066, respectively). VEGF-C showed no significant modifications. Previous determinations of VEGF and TSP-1 in the same patients were utilized. VEGF/sVEGFR-2, VEGF/TSP-1, and VEGF-C/sVEGFR-3 ratios decreased significantly along the treatment (P = 0.0092; P = 0.0072; P = 0.0141, respectively). Nonsignificant variations were observed for VEGF-C/sVEGFR-2 ratio. Baseline values of VEGF/sVEGFR-2 and VEGF/TSP-1 ratios were associated with time to progression (TTP) (P = 0.0407; P = 0.0394, respectively) meanwhile baseline VEGF was marginally significant (P = 0.0716). Patients with values lower than the 50 th percentile for both ratios showed longer TTP. Conclusions: We have identified the baseline VEGF/sVEGFR-2 and VEGF/TSP-1 ratios as potential biomarkers of response in ABCP treated metronomically with Cy+Cel. This finding warrants its confirmation in a higher number of patients.