HER2-positive breast cancers account for 15%-20% of all breast cancers. Despite trastuzumab has significantly improved the survival of patients with HER2-positivie metastatic breast cancer as the first-line standard treatment, the selection of drugs after trastuzumab treatment failure remains difficulty and challenge. Inetetamab, a new antibody to optimize the ADCC effect, has shown great effectiveness in treating HER2-positive metastatic breast cancer, but therapies subsequent to trastuzumab progression are still controversial. Pyrotinib, another second-line HER2 targeted drug, is a typical representative of TKI drugs, which not only has a strong HER2 antagonistic effect but also can synergize with monoclonal antibodies to amplify the ADCC effect. Here, investigators studied the efficacy and safety of inetetamb combined with pyrotinib and vinorelbine as first-line to third-line treatment after trastuzumab progression, so as to provide new ideas for the treatment of patients with HER2-positive metastatic breast cancer.