Trastuzumab is an important agent for the treatment of patients with HER2-positive metastatic breast cancer. However, a considerable number of patients will develop resistance to trastuzumab treatment. Previous studies have shown that multiple mechanisms mediate trastuzumab resistance, such as abnormal extracellular domain of the HER2 receptor, HER3 mutation and activation of bypass signaling pathway. To overcome these resistance mechanisms, the combination of trastuzumab with HER2-targeting tyrosine kinase inhibitor (TKI) is an effective strategy. In this phase 2 single-arm clinical trial, 30 patients with HER2-positive metastatic breast cancer after progression on trastuzumab are enrolled and receive treatment of Inetetamab plus Pyrotinib plus Oral Vinorelbine. The study aimed to access the efficacy and safety of Inetetamab combined with Pyrotinib and Oral Vinorelbine in HER2-positive metastatic breast cancer patients after progression on trastuzumab. The primary end point is Progressive-free Survival (PFS). The secondary end points are Overall Survival (OS), Overall Response Rate (ORR), Clinical Benefit Rate (CBR) and safety.
