Sponsor discretion (low recruitment rate)

This is a phase 4, multi-center, open-label, prospective cohort study to evaluate the clinical utility of Fluoroestradiol F18 (Cerianna) PET/CT to guide therapeutic management in ER-positive, HER2-negative metastatic breast cancer patients with progressive disease on first-line standard-of-care hormonal therapy. All patients will undergo a Cerianna PET/CT scan. The treating physician will complete a standardized questionnaire to indicate the second-line therapeutic management plan before the scheduled Cerianna PET/CT. After interpretation of Cerianna PET/CT by local radiologist or nuclear medicine physician, the treating physician will fill out a similar questionnaire to specify the final therapeutic decision. The proportion of patients with a change in therapeutic management plan based on Cerianna PET/CT results will be the primary endpoint. During the study follow-up period of 18 months, data on standard-of-care imaging, treatments/procedures received, and clinical outcomes will be collected. Patients will be asked to complete a health-related quality of life questionnaire at their screening, 6-month, and 18-month visit. Secondary endpoints include visual and quantitative heterogeneity assessment of tumor Cerianna uptake, and PFS rates at 6 months and 18 months after Cerianna PET/CT, which will be assessed between patients with and without a change in therapeutic management plan. Maximum duration of follow-up for each patient: 20 months. First patient first visit to last patient last visit: estimated 36 months.

Inclusion Criteria:

• Patient must sign informed consent prior to enrollment in this trial
• The patient is a female ≥18 years old
• Post-menopausal or pre-menopausal patient with known primary breast tumor(s) expressing ER in ≥1% of tumor cells by IHC
• HER2-negative (0, 1+, 2+ fluorescence in situ hybridization (FISH) negative) primary lesion
• MBC with at least 1 identifiable lesion on standard-of-care imaging assessment, outside of the liver, as confirmed by the investigator site
• Patient with progressive disease on 1st line hormonal therapy (Aromatase Inhibitor) with or without a CDK4/6 inhibitor or mechanistic target of rapamycin (mTOR) inhibitor or phosphoinositide 3-kinases (PI3K) inhibitor
• Patient must score at least 0, 1 or 2 on the Eastern Cooperative Oncology Group (ECOG) Performance Status
• Life expectancy of at least 12 months
• The patient is planned to undergo a standard-of-care imaging scan (according to National Comprehensive Cancer Network guidelines, e.g., CT and/or bone scan, or fluorodeoxyglucose [FDG]-PET/CT) covering chest, abdomen, and pelvis after date of consent and before Cerianna PET/CT (Visit 2), or the patient has undergone recent standard-of-care imaging before date of consent and is planned to undergo Cerianna PET/CT (Visit 2) no more than 45 days from the standard-of-care imaging scan

Exclusion Criteria:

• Isolated hepatic metastases (taking into account the physiological hepatic high uptake of Cerianna)
• Patient is on tamoxifen/toremifene treatment without 8-week washout, or on fulvestrant treatment without 28-week washout, (may block ER) before Cerianna PET/CT
• Other evolutive malignant disease (non-melanoma skin cancer is allowed) or acute or chronic infectious disease (well-controlled infectious disease is allowed);
• Patient has a history of administered chemotherapy for metastatic disease; prior chemotherapy in the (neo)adjuvant setting is allowed
• Patient with a known allergy to any of the components of Cerianna
• Woman of childbearing age who is not using effective contraception
• Pregnant woman (per the Product Label and ensured using clinic's standard-of-care), or parturient or nursing mother
• Patient presents with any other clinically active, serious, life-threatening disease, medical, or psychiatric condition, and/or who has a life expectancy of <12 months, or for whom study participation may compromise their management; and/or a patient who the investigator judges to be unsuitable for participation in the study for any reason
• Inability to comply with any requirements of the protocol

Metastatic Breast Cancer Patients with ER-Positive and HER2-Negative Primary Lesions after Progression on First Line Hormonal Therapy