[18F]Fluoroestradiol-PET/CT Companion Imaging Study to the FORESEE Trial

Inclusion Criteria:

Adults aged 18 years or greater.
All patients or legal guardians are willing and able to sign written informed consent and HIPAA authorization in accordance with local and institutional guidelines.
Enrolled on the FORESEE trial.
Biopsy proven estrogen receptor positive breast cancer.
Patient deemed refractory to all combinations of hormonal therapies by FORESEE trial investigators.

Exclusion Criteria:

Patients with known allergic or hypersensitivity reactions to previously administered radiopharmaceuticals. Patients with significant drug or other allergies or autoimmune diseases may be enrolled at the Investigator's discretion.
Patients who require monitored anesthesia for PET/CT scanning.
Patients who are too claustrophobic to undergo PET/CT scanning.
Patients who are pregnant or currently breast feeding.
Any patient that is medically unstable defined as a patient requiring inpatient hospitalization or needing evaluation at an acute care or urgent care facility at the time of imaging.