18F-fluoroestradiol (FES) positron emission tomography (PET) scans measure regional estrogen binding, and 18F-fluorodeoxyglucose (FDG) PET measures tumor glycolytic activity

FDG PET and FES PET predict PFS on endocrine therapy:

PURPOSE: 18F-fluoroestradiol (FES) positron emission tomography (PET) scans measure regional estrogen binding, and 18F-fluorodeoxyglucose (FDG) PET measures tumor glycolytic activity. We examined quantitative and qualitative imaging biomarkers of progression-free survival in breast cancer patients receiving endocrine therapy. EXPERIMENTAL DESIGN: Ninety patients with breast cancer from an estrogen receptor positive, HER2-negative primary tumor underwent FES PET and FDG PET scans prior to endocrine therapy (63% aromatase inhibitor, 22% aromatase inhibitor and fulvestrant, 15% other). Eighty-four had evaluable data for progression-free survival prediction. RESULTS: Recursive partitioning with fivefold internal cross-validation used both FES PET and FDG PET measures to classify patients into three distinct response groups. FDG PET identified 24 patients (29%) with low FDG uptake, suggesting indolent tumors. These patients had a median progression-free survival of 26.1 months (95% confidence interval 11.2-49.7). Of patients with more FDG-avid tumors, 50 (59%) had high average FES uptake, and 10 (12%) had low average FES uptake. These groups had median progression-free survival of 7.9 (5.6-11.8) and 3.3 months (1.4-not evaluable), respectively. Patient and tumor features did not replace or improve the PET measures' prediction of progression-free survival. Prespecified endocrine resistance classifiers identified in smaller cohorts did not individually predict progression-free survival. CONCLUSION: A wide range of therapy regimens are available for treatment of ER+ metastatic breast cancer, but no guidelines are established for sequencing these therapies. FDG PET and FES PET may help guide the timing of endocrine therapy and selection of targeted and/or cytotoxic chemotherapy. A multicenter trial is ongoing for external validation.



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