The aim of this study is to test the hypothesis that antiangiogenic treatment with sunitinib consolidation can prolong remissions induced by taxane-based chemotherapy in women with metastatic breast cancer. The method involves a two-arm open-label (2:1 randomization) multicenter, randomized phase II trial evaluating the efficacy of sunitinib (arm A) versus no therapy (arm B) in patients with HER-2-negative metastatic breast cancer who achieved an objective response to taxane-based chemotherapy. The results of this study indicates that the primary endpoint of progression-free survival (PFS) > or =5 months was achieved in 10 of 36 patients (28%) in arm A and 4 of 19 patients (21%) in arm B. The median PFS was 2.8 and 3.1 months, respectively. A protocol amendment to the sunitinib dosing schedule was made because 53% (17/32) of patients treated at a starting dose of 50 mg (4 weeks on/2 weeks off) required dose reduction. Changing the starting dose to sunitinib 37.5 mg continuously resulted in dose reductions in 44% (7/16) of patients. Grades III-IV toxicity occurred in 69% of patients in arm A (fatigue 31%, musculoskeletal pain 11%, neutropenia and thrombopenia 8%) and 11% in arm B. The proof-of-principle study does not confirm the hypothesis that sunitinib consolidation therapy can lead to a predefined clinically relevant proportion of patients with PFS of > or =5 months after an objective response to taxanes. Furthermore, toxicity was significant.