¹⁸F-FDG PET/CT for the Evaluation of Therapy Response in Hormone Receptor–Positive Bone-Dominant Metastatic Breast Cancer

Fluorine 18 (18F) fluorodeoxyglucose (FDG) PET/CT has shown promise for use in assessing treatment response in patients with bone-only or bone-dominant (BD) metastatic breast cancer (mBC). In this single-institution, prospective single-arm study of 23 women (median age, 59 years [range, 38-81 years]) with biopsy-proven estrogen receptor-positive bone-only or BD mBC about to be-gin new endocrine therapy between October 3, 2013, and August 3, 2018, the value of early 4-week18F-FDG PET/CT in predicting progression-free survival (PFS) was evaluated. 18F-FDG PET/CT was performed at baseline, 4 weeks, and 12 weeks. Maximum stan-dardized uptake value (SUVmax) and peak SUV (SUVpeak) were measured for up to five index lesions. The primary end point was PFS. Secondary end points were overall survival (OS) and time to skeletal-related events (tSREs). All end points were compared between responders (reduction of 30% or more in the sum of SUVmax for target lesions) and nonresponders at 4 weeks and 12 weeks. Percentage change from baseline in SUVmax at 4-and 12-week18F-FDG PET/CT were highly correlated (r = 0.81). At the 4-week time point PET responders had numerically longer PFS (14.2 months vs 6.3 months; P = .53), OS (44.0 months vs 29.7 months; P = .47), and tSRE (27.4 months vs 25.2 months; P = .66) compared with nonresponders, suggesting the clinical utility of 4-week18F-FDG PET/CT as an early predictor of treatment failure.