First results of molecular imaging (FDG and FES) in prospective study for selecting second line hormonotherapy in estrogen receptors positive metastatic breast cancer patients

Aim/Introduction: About 70% of primitive breast cancers had positive estrogen receptors (ER) and may benefit from hormonotherapy. However, ER expression in breast cancer metastases is heterogeneous and about 15% of metastases lost this expression over time. Biopsies were not possible systematically. 16α-18Fluoro-17β-Oestradiol (18FES) is a radiopharmaceutical which predict the response to the first line hormonotherapy. The aim of this prospective study (NCT03442504) was to determine the predictive value of PET at the patient level, before a second line hormonotherapy (2nd- HT) on the FDG response obtained at 6 weeks of treatment. Materials and Methods: We prospectively included 12 ER+ metastatic breast cancer patients, HER2 negative, in progression despite first line hormonotherapy. For the complete study, 60 patients will be included. Due to 2nd-HT proposed by oncologist, we performed 18FES PET-CT (18FES-BL) and 18FDG PET-CT (18FDG-BL) at baseline in the month before the new treatment introduction. Follow-up with 18FDG PET-CT and CT