Integrated whole-body magnetic resonance imaging (MRI)-positron emission tomography (PET) scanners have recently been introduced for clinical use. This technology combines the anatomic and perfusion data obtained with dynamic contrast enhanced (DCE) MRI with functional imaging data obtained from PET. For breast imaging, the combination of MRI and PET has important potential to improve diagnostic accuracy and provide molecular characterization of breast cancer. The overall purpose of this research is to test the accuracy of PET/MRI imaging with 18F-fluorofuranylnorprogesterone (FFNP) for measuring progesterone receptor (PR) expression in patients with invasive breast cancer.