M7824 in Treating Patients With Stage II-III HER2 Positive Breast Cancer

PRIMARY OBJECTIVE: I. To evaluate the change in tumor-infiltrating lymphocytes (TIL) percentage pre and post M7824 therapy. SECONDARY OBJECTIVES: I. To evaluate the safety and tolerability of M7824 in early stage breast cancer (stage II/III). II. To evaluate pathological response at the time of surgery after 2 doses of M7824 followed by neoadjuvant (human epidermal growth factor receptor 2) HER2 targeted therapy in combination with chemotherapy of physician's choice. EXPLORATORY OBJECTIVES: I. To evaluate imaging based response to M7824. II. To evaluate potential systemic and tumor based predictive biomarker candidates of response. III. To evaluate immune responses induced by exposure to M7824 systemically and in tumor microenvironment (TME). OUTLINE: Patients receive anti-PD-L1/TGFbetaRII fusion protein M7824 intravenously (IV) over 1 hour on days 1 and 15. During days 28-56 patients receive planned neoadjuvant chemotherapy.