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Background: Despite significant survival improvement in human epidermal growth factor receptor 2 (HER2) blockade for HER2-positive breast cancer, resistance to anti-HER2 remains inevitable. Subsequent anti-HER2 with continuing trastuzumab beyond progression is acceptable with limited efficacy when other anti-HER2 treatment is unavailable. This single-arm, phase II study (SYSUCC-005) aimed to explore the efficacy of switching mode for HER2-positive refractory metastatic breast cancer.Methods: Patients with HER2-positive metastatic breast cancer rapidly progressing during pre-trastuzumab from six hospitals in China were designed to switch to lapatinib 1,250 mg orally once per day continuously plus capecitabine (1,000 mg/m2 orally twice per day on days 1-14) or vinorelbine (25 mg/m2 intravenously once per day on days 1 and 8) of each 21-day cycle. The primary endpoint was progression-free survival (PFS).Results: Between January 5, 2015 and May 31, 2020, 159 patients were eligible in this study. The median follow-up was 33.1 months, a median PFS of 8.5 months was achieved. Brain metastases (hazard ratio [HR] = 1.582, 95% confidence interval [CI] 1.019- 2.453, P = 0.041) and ≥ 2 metastatic sites (HR = 1.679, 95% CI 1.151-2.450, P = 0.007) were independent prognostic factors for PFS. The most common grade ≥ 3 adverse events were diarrhea (3.8%) and hand-foot syndrome (9.4%).Conclusion: The switching mode showed predominant efficacy, which might be a prior therapeutic option over continuing mode in subsequent anti-HER2 therapy for patients with HER2-positive refractory metastatic breast cancer.Trial Registration: This trial was registered on ClinicalTrials.gov ( NCT02362958 ) on 13/02/2015. [ABSTRACT FROM AUTHOR]