In a small study at Johns Hopkins, women were treated with partial breast irradiation and chemotherapy given at the same time. We are now testing in a bigger study whether giving partial breast irradiation and chemotherapy at the same time (our new method) has the same side effects and outcomes as giving partial breast irradiation and chemotherapy at different times(older method). In this study women who had their breast cancer removed but need radiation to the breast will be randomized to partial breast irradiation at the same time as chemotherapy or partial breast radiation at a different time than chemotherapy. Randomization is like flipping a coin but in this study about 2 of every 3 women will get the new method.

To compare how often cancer recurs (comes back) after 3 weeks of radiation compared to 5 weeks of radiation in patients who receive radiation therapy delivered to the lymph nodes near the breast. The side effects that can develop during or after radiation treatment, including how often arm swelling (edema) happens, will also be studied

This study will evaluate the efficacy, safety, and pharmacokinetics of adjuvant atezolizumabwhen given in combination with trastuzumab emtansine compared with placebo andtrastuzumab emtansine for patients with residual invasive HER2-positive breast cancerfollowing neoadjuvant taxane-based and HER2-targeted therapy including trastuzumab, whoare at high risk of disease recurrence. The primary endpoint for this study is invasivedisease-free survival (IDFS).