Study design and participants
Tumors
ONCOLOGY, METASTATIC BREAST CANCER, TUMORS
This was an investigator-initiated, single-arm, phase 2 trial conducted at 16 sites in China. Patients were included if they were females aged 18–70 years; had pathologically confirmed HER2-positive (score 3 + by immunohistochemistry, or 2 + with positive results of fluorescence in-situ hybridization) locally advanced or metastatic breast cancer; had primary resistance to trastuzumab; had an Eastern Cooperative Oncology Group performance status of 0 or 1; had known hormone receptor status; had an expected survival of ≥ 3 months; had at least one measurable lesion according to the Response Evaluation Criteria In Solid Tumors (RECIST), version 1.1 [The study was conducted in accordance with the Declarations of Helsinki and Good Clinical Practice and was approved by the ethics committee of each participating center. Written informed consent was obtained from each patient. The study was registered with ClinicalTrials.gov, NCT04001621.