Heterogeneity of bone metastases as an important prognostic factor in patients affected by oestrogen receptor-positive breast cancer. The role of combined [18F]Fluoroestradiol PET/CT and [18F]Fluorodeoxyglucose PET/CT

•Glucose metabolism using FDG and oestrogen receptor using FES was evaluated in BC patients with bone metastases, candidate to endocrine therapy.•Entity of FDG uptake was the sole predictor of progression-free survival.•Neither FDG nor FES could predict overall survival. However, the combined assessment, as FES/FDG ratio, correlated with this parameter.•These findings suggest that the combination of metabolic aggressivity and low oestrogen receptor expression are predictor of poor prognosis.