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 Known or suspected MBC with at least 1 identifiable lesion on conventional imaging assessment, outside of the liver, as confirmed by the investigator site Patient with known MBC or suspected MBC that meets one of the following: Known MBC with no prior treatment Patient with known MBC after 1st line or 2nd line hormone therapy with or without a CDK4 inhibitor or mTOR inhibitor or PI3K inhibitor Patient with suspected MBC who is intended to receive either 1st line standard-of-care therapy or receive 2nd line standard-of-care therapy 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 must have undergone a conventional imaging scan (according to National Comprehensive Cancer Network guidelines, e.g., CT and/or bone scan) covering chest, abdomen, and pelvis no more than 45 days before screening  Exclusion Criteria:  Isolated hepatic metastases (taking into account the physiological hepatic high uptake of Cerianna) Patient is on tamoxifen and fulvestrant treatment without 8- and 28-weeks washout, respectively, (may block ER) before Cerianna PET/CT Other evolutive malignant disease or acute or chronic infectious disease Patient has a history of >1 line of administered chemotherapy for metastatic disease and has not been off chemotherapy for a minimum of 2 weeks; prior chemotherapy in the 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