Imaging of in Vivo Sigma-2 Receptor Expression With 18F-ISO-1 Positron Emission Tomography in Metastatic Breast Cancer

Inclusion Criteria: * At least 18 years of age * Biopsy proven or clinically documented metastatic breast cancer with at least one lesion outside the liver by standard imaging (e.g. CT, MRI, Bone Scan, Ultrasound, FDG PET/CT) * Plan to start new systemic therapy for metastatic disease. * Participants must be informed of the investigational nature of this study and be willing to provide written informed consent and participate in this study in accordance with institutional and federal guidelines prior to study-specific procedures. Exclusion Criteria: * Females who are pregnant at the time of screening will not be eligible for this study, urine or serum pregnancy test will be performed in women of child-bearing potential at the time of screening. * Inability to tolerate imaging procedure in the opinion of an investigator or treating physician. * Serious or unstable medical or psychological conditions that, in the opinion of the investigator, would compromise the subject's safety or successful participation in the study.