FFNP-PET/MR Imaging of Progesterone Receptor Expression in Invasive Breast Cancer

Inclusion Criteria: * Women 18 years of age or older * Diagnosis of biopsy-proven invasive breast cancer measuring at least 1.0 cm in diameter by any imaging modality * Biopsy-proven PR-positive or PR-negative invasive breast cancer * Undergoing diagnostic breast MRI ordered by the referring clinician for staging and extent of disease Exclusion Criteria: * Inability or unwillingness to provide informed consent to the study * Participants currently undergoing neoadjuvant chemotherapy/endocrine therapy or those who have received chemotherapy/endocrine therapy within 6 months prior to the MRI * Participants who have had neoadjuvant chemotherapy/endocrine therapy, surgical intervention, or radiation for the current biopsy-proven malignancy * Participants with breast expanders * Participants who are or might be pregnant or lactating * Participants with a contraindication to gadolinium based contrast agents, including allergy or impaired renal function (per University of Wisconsin Health Guidelines) * Participants with a history of allergic reaction attributable to compounds of similar chemical or biologic composition to FFNP * Participants in liver failure as judged by the patient's physician * Participants with standard contraindications to MRI, including claustrophobia and metallic implants incompatible with MRI * Participants requiring intravenous (IV) conscious sedation for imaging are not eligible; participants requiring mild, oral anxiolytics for the clinical MRI will be allowed to participate as long as the following criteria are met: * The subject has their own prescription for the medication * The informed consent process is conducted prior to the self-administration of this medication * They come to the research visit with a driver * Participants unable to lie prone for 30 minutes for imaging