<sup>18</sup>F-fluoroestradiol (FES) PET/CT could non-invasively reveal ER expression both in primary and metastatic breast cancer and recognize heterogeneity of ER status.<h4>Case presentation</h4>A 70-year-old woman with Parkinson's disease, osteoporosis and cardiovascular co-morbidity was diagnosed with HR+/HER2- breast cancer (pT2N2M0, stage IIIa). This evidence concerns the gene ESR1 and breast cancer.