Monitoring Early Response to Targeted Therapy in Stage IV HER2+ Breast Cancer Patients With Advanced PET/MR Imaging

The purpose of this study is to see if a new group of imaging tests can help identify response to stage IV human epidermal growth factor receptor 2 positive (HER2+) breast cancer before and during treatment. This study will test a new method for monitoring treatment. The investigators will use \[18F\]-Fluorodeoxyglucose (FDG) positron emission tomography (PET)/magnetic resonance imaging (MRI) to look at previously diagnosed stage IV breast cancer and image up to three times during therapy. FDG is a non-natural amino acid with a radioactive tag that is used clinically for staging of disease. However, the role of FDG-PET/MRI for imaging response in breast cancer is not currently clear. PET/MRI is a new imaging technique that combines PET and MRI into a single study.