Here we report a phase I study that evaluated the safety, activity, and biomarkers of LZM005, a HER2 antibody, used as a monotherapy or in combination with trastuzumab plus docetaxel in patients with HER2-positive MBC….In phase Ia, partial response (PR) was achieved in one case (1/14, overall response rate [ORR]: 7.1%); the disease control rate was 42.90% (6/14). In phase Ib, 11 patients (55.0%) achieved PR, and eight (40.0%) had stable disease. The ORR was 100% (6/6) in trastuzumab-naive and 35.7% (5/14) in trastuzumab-pretreated patients.