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

Fluorine 18 ( 18 F) 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 begin new endocrine therapy between October 3, 2013, and August 3, 2018, the value of early 4-week 18 F-FDG PET/CT in predicting progression-free survival (PFS) was evaluated. 18 F-FDG PET/CT was performed at baseline, 4 weeks, and 12 weeks. Maximum standardized uptake value (SUV max ) and peak SUV (SUV peak ) 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 SUV max for target lesions) and nonresponders at 4 weeks and 12 weeks. Percentage change from baseline in SUV max at 4- and 12-week 18 F-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-week 18 F-FDG PET/CT as an early predictor of treatment failure. Keywords: Breast Cancer, Metastatic Breast Cancer, Bone-Dominant Metastatic Breast Cancer, FDG PET/CT, Estrogen-Receptor Positive Metastatic Breast Cancer Supplemental material is available for this article. Clinical trial registration no. NCT04316117 © RSNA, 2022.