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

PurposeTo compare [F-18]-fluorodeoxyglucose (FDG) and [F-18]-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 8weeks in bone-predominant metastatic breast cancer.Patients and methodsThirty-one patients scheduled for endocrine therapy had up to five bone metastases measured [FDG, NaF PET/CT: maximum standardized uptake value (SUVmax); WB-MRI: median apparent diffusion coefficient (ADC(med))] at baseline and 8weeks. 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).ResultsTwenty-two patients (median age, 58.6years, range, 40-79years) 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 ADC(med), 0, 100 and 72.2%, respectively.PFS<24weeks 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 ADC(med) (-0.5 vs. 10.1%, p=0.098). Interlesional response heterogeneity occurred in all modalities and NaF flare occurred in seven patients.ConclusionsFDG PET/CT and WB-MRI best predicted clinical non-PD and both FDG and NaF PET/CT predicted PFS<24weeks. Lesional response heterogeneity occurs with all modalities and flare is common with NaF PET/CT.