The AVIATOR Study: Trastuzumab and Vinorelbine With Avelumab OR Avelumab & Utomilumab in Advanced HER2+ Breast Cancer

This research study is studying a combination of drugs as a possible treatment for breast cancer. The drugs involved in this study are: - Group A: Trastuzumab (Herceptin) + Vinorelbine (Navelbine) - Group B: Trastuzumab + Vinorelbine + Avelumab - Group C: Trastuzumab + Vinorelbine + Avelumab + Utomilumab (PF-05082566)