D4 Choline Breast PET/CT

Inclusion Criteria: 1. Female patients with a histological diagnosis of locally advanced or metastatic estrogen-receptor positive, HER2 negative breast cancer 2. Written informed consent prior to admission in the study. 3. Target lesion diameter of ≥15mm that has not been previously irradiated and is located outside the liver 4. Female patients aged ≥ 18 years of age 5. For all patients: histologically confirmed locally advanced/ metastatic breast cancer with a previous biopsy confirming hormone receptor and HER2 status 6. ECOG performance status 0-2 7. Negative urine pregnancy test (within 2 hours prior to injection of imaging agent) in women of child bearing age and willingness to use contraception (barrier, abstinence, non-hormonal) for 3 weeks after injection of \[18F\]D4-FCH 8. Life expectancy \> 3months 9. Adequate organ function as judged by investigator to include: * Hb≥ 10g/L * Creatinine clearance ≥45ml/min 10. Patients must have been appropriately staged (which may include contrast enhanced CT/ FDG-PET/ MRI) within 42 days of study entry and additional imaging according to local standard of care Exclusion Criteria: 1. Pregnant or lactating women 2. Evidence of significant medical condition or laboratory finding which, in the opinion of the Investigator, makes it undesirable for the patient to participate in the trial 3. Participants with severe claustrophobia or who are unable to lie flat or fit into the scanner (≥350 lbs (160 Kg)) 4. Prior use within 14 days of enrolment or concurrent therapy with any other investigational agent 5. Patients classified as radiation workers 6. Patient has previously received treatment with CDK 4/6 inhibitors