Clinical Trial of Atezolizumab With Paclitaxel, Trastuzumab, and Pertuzumab in Patients With Metastatic HER-2 Positive Breast Cancer

This is a single arm, Phase IIA clinical trial assessing the safety and efficacy of atezolizumab in combination with paclitaxel, trastuzumab, and pertuzumab in 50 patients with locally advanced, unresectable, or metastatic HER2-overexpressing breast cancer. Due to concerns that corticosteroids may have a negative effect on tumor immunity expected with addition of atezolizumab to the standard of care regimen, patients will receive premedication with dexamethasone only for weeks 1 and 2 of the weekly paclitaxel, and then corticosteroid premedication will be discontinued subsequently. Patients must have pathologically confirmed HER2-overexpressing breast cancer that is locally recurrent, unresectable, or metastatic, with measurable disease as defined by RECIST v1.1. Tumor measurements and bone scans will be performed every 9 weeks while patients are on study.