Quantitative fluoroestradiol positron emission tomography imaging predicts response to endocrine treatment in breast cancer

Purpose In breast cancer, [F-18]fluoroestradiol (FES) positron emission tomography (PET) correlates with estrogen receptors (ER) expression and predicts response to tamoxifen. We tested the ability of FES-PET imaging to predict response to salvage hormonal treatment in heavily pretreated metastatic breast cancer patients, predominantly treated with aromatase inhibitors. Patients and Methods Initial FES uptake measurements in 47 patients with ER-positive tumors were correlated with subsequent tumor response to 6 months of hormonal treatment. Most patients had bone dominant disease and prior tamoxifen exposure. Response was compared to initial FES-PET uptake, measured qualitatively and quantitatively using standardized uptake value (SUV) and estradiol-binding flux. Results Eleven of 47 patients (23%) had an objective response. While no patients with absent FES uptake had a response to treatment, the association between qualitative FES-PET results and response was not significant (P =.14). However, quantitative FES uptake and response were significantly associated; zero of 15 patients with initial SUV less than 1.5 responded to hormonal therapy, compared with 11 of 32 patients (34%) with SUV higher than 1.5 (P <.01). In the subset of patients whose tumors did not overexpress HER'/neu, 11 of 24 patients (46%) with SUV higher than 1.5 responded. Conclusion Quantitative FES-PET can predict response to hormonal therapy and may help guide treatment selection. Treatment selection using quantitative FES-PET in our patient series would have increased the rate of response from 23% to 34% overall, and from 29% to 46% in the subset of patients lacking HER'/neu overexpression. A multi-institutional collaborative trial would permit definitive assessment of the value of FES-PET for therapeutic decision making.