Purpose

This trial studies the best dose and side effects of utomilumab (4-1BB agonist monoclonal antibody PF-05082566) with trastuzumab emtansine or trastuzumab in treating patients with HER2-positive breast cancer that has spread to other places in the body. Monoclonal antibodies, such as utomilumab, trastuzumab emtansine, and trastuzumab may interfere with the ability of tumor cells to grow and spread.