Described herein methods of using antigen-binding constructs to treat HER2+ tumors in a subject such as breast, lung, or head and neck tumors. In some aspects, the tumor volume in the subject after receiving at least seven doses of the antigen binding construct is less than the tumor volume of a control subject receiving an equivalent amount of trastuzumab. In some aspects, the survival of the subject receiving the antigen binding construct is increased as compared to a control subject receiving an equivalent amount of a non-specific control antibody or as compared to a control subject not receiving treatment.
