Metabolic flare: Indicator of hormone responsiveness in advanced breast cancer

Purpose: The purpose of this study was to investigate whether positron emis sion tomography (PET) with the glucose analog [F-18]fluorodeoxyglucose (FDG ) and the estrogen analog 16 alpha-[F-18]fluoroestradiol-17 beta (FES), per formed before and after treatment with tamoxifen, could be used to detect h ormone-induced changes in tumor metabolism (metabolic flare) and changes in available levels of estrogen receptor (ER), In addition, we investigated w hether these PET findings would predict hormonally responsive breast cancer , Patients and Methods: Forty women with biopsy-proved advanced ER-positive ( ER+) breast cancer underwent PET with FDG and FES before and 7 to 10 days a fter initiation of tamoxifen therapy; 70 lesions were evaluated. Tumor FDG and FES uptake were ossessed semiquantitatively by the standardized uptake value (SUV) method. The PET results were correlated with response to hormon al therapy, Results: In the responders, the tumor FDG uptake increased after tamoxifen by 28.4% +/- 23.3% (mean SD); only five of these patients had evidence of a clinical flare reaction, In nonresponders, there was no significant change in tumor FDG uptake from baseline (mean change, 10.1% +/- 16.2%; P = .0002 v responders). Lesions of responders had higher baseline FES uptake (SUV, 4.3 +/- 2.4) than those of nonresponders (SUV, 1.8 +/- 1.3; P = .0007), All patients had evidence of blockade of the tumor ERs 7 to 10 days after init iation of tamoxifen therapy; however, the degree of ER blockade wets greate r in the responders (mean percentage decrease, 54.8% +/- 14.2%) than in the nonresponders (mean percentage decrease, 19.4% +/- 17.3%; P = .0003). Conclusion: The functional status of tumor ERs can be characterized in vivo by PET with FDG and FES, The results of PET are predictive of responsivene ss to tamoxifen therapy in patients with advanced ER+ breast cancer.