Simultaneous whole-body multi-parametric 2-[18F]FDG-PET/MRI in smoldering multiple myeloma assessment : diagnostic and prognostic impact

The co-primary aims of this study were to assess the diagnostic and prognostic performance of Whole-body-2-[¹⁸F]-fluorodeoxyglucose-positron emission tomography coupled with MRI (WB-2-[¹⁸F]FDG-PET/MRI) imaging in the smoldering multiple myeloma (SMM) workup for detection of MM-related medullary or extra-medullary disease and for the prediction of progression-free survival (PFS) defined as time to progression to symptomatic MM requiring therapy. A total of 116 patients with SMM (without CRAB or SLiM criteria before imaging) were prospectively included in the study and underwent full multi-parametric WB-2-[¹⁸F]FDG-PET/MRI imaging. PET detected at least one FL > 5 mm in 9% of patients compared to 20% on MRI (p = 0.02). PET detected diffuse bone marrow involvement (BMI) in 20% of patients and MRI in 53% (p < 10^{− 3}). A total of 98 patients with true SMM not requiring treatment were then followed up. The presence of diffuse BMI on MRI was the strongest adverse prognostic parameter for PFS (univariate: hazard ratio (HR), 6.12; p < 10^{− 2}. Multivariate : HR, 4.16; p = 0.03) and could be proposed as a new high-risk biomarker for progression to symptomatic MM. Dynamic contrast-enhanced (DCE)-MRI based increased peak enhancement intensity (PEI) and maximum intensity time ratio (MITR) values were other strong adverse prognostic factors.