Prediction of therapy response in bone predominant metastatic breast cancer: Comparison of [18F-] fluorodeoxyglucose and [18F]-fluoride PET/CT with whole-body MRI with diffusion weighted imaging.

Purpose To compare [18F]-fluorodeoxyglucose (FDG) and [18F]-sodium fluoride (NaF) positron emission tomography/computed tomography (PET/CT) with whole-body magnetic resonance with diffusion-weighted imaging (WB-MRI), for endocrine therapy response prediction at 8 weeks in bone-predominant metastatic breast cancer. Patients and Methods Thirty-one patients scheduled for endocrine therapy had up to 5 bone metastases measured [FDG, NaF PET/CT: maximum standardized uptake value (SUVmax); WB-MRI: median apparent diffusion coefficient (ADCmed)] at baseline and 8 weeks. To detect the flare phenomenon, a 12-week NaF PET/CT was also performed if 8-week SUVmax increased. A 25% parameter change differentiated imaging progressive disease (PD) from non-PD and was compared to a 24-week clinical reference standard and progression free survival (PFS). Results Twenty-two patients (median age 58.6 years, range 40-79 years) completing baseline and 8-week imaging were included in the final analysis. Per-patient % change in NaF SUVmax predicted 24-week clinical PD with sensitivity, specificity and accuracy of 60%, 73.3% and 70%, respectively. For FDG SUVmax the results were 0%, 100% and 76.2% and for ADCmed, 0%, 100% and 72.2%, respectively. PFS < 24 weeks was associated with % change in SUVmax (NaF: 41.7% vs 0.7%, p=0.039; FDG: -4.8% vs -28.6%, p=0.005) but not ADCmed (-0.5% vs 10.1%, p=0.098). Interlesional response heterogeneity occurred in all modalities and NaF flare occurred in 7 patients. Conclusion FDG PET/CT and WB-MRI best predicted clinical non-PD and both FDG and NaF PET/CT predicted PFS < 24 weeks. Lesional response heterogeneity occurs with all modalities and flare is common with NaF PET/CT.