Dynamic and Test-retest Whole Body [18F]FES PET Imaging in Patients With Metastatic ER+ Breast Cancer

Inclusion criteria

• Histologically proven metastatic ER+ (>10% positive stained cells using immunohistochemistry) breast cancer on the latest biopsy
• Postmenopausal females aged 18 years or older at screening. Postmenopausal status is defined as one of the following:

• age ≥60 years
• age <60 years and amenorrhea for >12 months in the absence of interfering hormonal therapies (such as LH-RH agonists and ER-antagonists)
• patient age <60 years using LH-RH agonists should continue LH- RH-agonists until after the PET procedures
• previous bilateral oophorectomy or medically confirmed ovarian failure
• [18F]FDG PET, CT and/or a bone scan should be performed as part of routine clinical staging (≤4 weeks prior to screening)
• Patients should have metastases in the scanning field of view, all located outside of the liver
• Eastern Cooperative Oncology Group Performance Status (ECOG PS) of 0-2
• Estimated glomerular filtration rate (eGFR) ≥30 ml/min
• Written and signed informed consent

Exclusion criteria

• History with another cancer within the last 5 years, except cancer treated with curative intent and no evidence of disease as judged by the treating physician
• Use of selective estrogen receptor modulators (SERMs) or downregulators (SERDs) for current breast cancer such as Tamoxifen/Fulvestrant (≤5 weeks prior to screening) or investigational drug therapy
• Pregnancy or lactating women
• Any medical, psychological or social condition that may interfere with the subject's safety and participation in the study, will lead to exclusion from this study