F-18 16 Alpha- Fluoroestradiol PET/CT Scan in Evaluating Endocrine Therapy Response in Participants with Newly Diagnosed, Estrogen Receptor Positive Metastatic Breast Cancer

Inclusion Criteria

• Patients must be capable and willing to provide informed consent.
• Patients of childbearing potential must have a negative urine or serum pregnancy test within 7 days prior to PET/CT imaging per institution’s standard of care.
• A female of child-bearing potential is any woman (regardless of sexual orientation, having undergone a tubal ligation, or remaining celibate by choice) who meets the following criteria: * Has not undergone a hysterectomy or bilateral oophorectomy; or * Has not been naturally postmenopausal for at least 12 consecutive months (i.e., has had menses at any time in the preceding 12 consecutive months).
• Medically stable as judged by patient’s physician.
• Life expectancy must be estimated at > 6 months.
• Patients must have an Eastern Cooperative Oncology Group (ECOG) performance status of 0-3 (restricted to ECOG performance status [PS] 0-2 if age > 70 years).
• Patients with known allergic or hypersensitivity reactions to previously administered radiopharmaceuticals of similar chemical or biologic composition to FES are NOT eligible.
• Patients with liver failure are NOT eligible.
• Patient must NOT be breastfeeding.
• Histologically confirmed estrogen receptor positive (ER+) breast cancer either from a metastatic biopsy or from a primary breast tumor with imaging evidence of metastatic disease. The pathology report and either (1) tumor tissue (blocks or unstained slides) or (2) a photomicrograph of the ER immunohistochemistry (IHC) slide from at least one site of metastatic disease and/or from primary breast cancer must be available for review and analysis.
• No prior endocrine therapy for metastatic disease is allowed (i.e. must be first-line endocrine therapy for metastatic disease). However, a history of adjuvant endocrine therapy is allowed, as long as the date of diagnosis of metastatic disease is > 2 years following initiation of adjuvant endocrine therapy. Patients who develop metastatic disease while still receiving adjuvant endocrine therapy must have a change in the type of endocrine agent used for subsequent metastatic disease treatment. Patients on blocking adjuvant therapy (with a blocking agent such as toremifene or tamoxifen) must be off the agents for a minimum of 60 days to allow for adequate uptake of FES.
• Patients with human epidermal growth factor-2 positive (HER2+) metastatic tumors are NOT eligible.
• Patient must NOT be planning to receive everolimus nor human epidermal growth factor receptor 2 (HER2) directed therapy in addition to endocrine therapy.
• Postmenopausal women, men, or premenopausal women for whom endocrine therapy (tamoxifen, aromatase inhibitor [AI] with or without ovarian suppression or fulvestrant), with or without a CDK4/6 inhibitor is planned after FES-PET/CT is completed.
• Disease may be measurable (by Response Evaluation Criteria in Solid Tumors [RECIST] 1.1 criteria) or non-measurable but must be present in at least one non-liver site, 1.5 cm or greater and visualized on PET/CT with [18F]-fluorodeoxyglucose (FDG). Patients with effusion only disease or disease only in the liver are not eligible for the study.
• Patient must be able to lie still for a 20 to 30 minute PET/CT scan.