Evaluation of tumour heterogeneity by 18 F-fluoroestradiol PET as a predictive measure in breast cancer patients receiving palbociclib combined with endocrine treatment.

F-FES-PET may provide a promising method for identifying and selecting candidate ER + /HER2- MBC patients who would most likely benefit from palbociclib combined with endocrine treatment and could serve as a predictive marker for treatment response. Trial registration NCT04992156, Date of registration: August 5, 2021 (retrospectively registered).