P-011: 18F-FDG PET/MRI for imaging minimal residual disease evaluation in Multiple Myeloma

Abstract

<h3>Background</h3> Functional imaging in Multiple Myeloma (MM) plays a crucial role in defining bone disease response. According to IMWG guidelines,18FDG PET/CT represents the only technique recognized to define imaging minimal residual disease (MRD) negativity. More recently, Whole body Diffusion Weighted Imaging (WB DWI)-MRI represents a non ionizing radiation imaging modality with a potential impact on evaluating myeloma bone disease response. Consequently, patients achieving both PET/CT and WB DWI-MRI negativity after treatment showed improved progression free survival (PFS) as compared to patients with single PET or MRI negativity. In the last years, a novel functional technique combining both 18FDG PET with WB DWI-MRI (PET/MRI) has been developed. In this study, we evaluated PET/MRI for bone disease response assessment in MM. <h3>Methods</h3> We retrospectively studied 27 patients (12 female and 15 male) affected by newly diagnosed active MM. All patients received a combined 18F-FDG PET/MRI registering T1w signal, T2w STIR (short tau inversion recovery) signal, DWI (diffusion weighted imaging) signal, mean ADC (apparent diffusion coefficient) value and SUV (standardized uptake volume) max value at diagnosis and at the end of the therapeutic program [after autologous stem cell transplantation (ASCT) or consolidation treatment]. PET and MRI negativity was assessed using Deauville score (DS) and MY-RADS Response Assessment Category (RAC). Median age of the entire cohort was 57 years (44-69). Considering high risk disease features, 7/27 cases were ISS III (25.9%), 2/27 were R-ISS III (7.4%) while 7/26 (26.9%) patients harbored high risk FISH abnormalities [including t(4;14), t(14;16) and del17p]. Bone lytic lesions were detected in almost all patients (24/27, 88.9%), followed by anemia (17/27, 63%), hypercalcemia (3/27, 11.1%) and renal injury (2/27, 7.4%). All patients received bortezomib-thalidomide-dexamethasone induction regimen followed by ASCT. <h3>Results</h3> At the end of the therapeutic program, the overall response rate was 92.6%, with 37% (10/27) achieving a complete response. Regarding baseline PET/MRI evaluation, focal lesions (FLs) were detected in 23 patients, with mean SUVmax of 4.4+/-2.78 and mean ADC of 963+/-264.6 mm2/s. End of treatment PET/MRI showed a PET negativity (DS<3) in 14/27 (51.9%) patients and an MRI negativity (MY-RADS<2) in 18/27 (66.7%) cases. With a median follow up of 33 months, patients with concomitant PET and MRI negativity showed improved PFS with respect to patients with PET or MRI positivity (not reached vs 58 months, p=0.0396). By multivariate analysis, concomitant PET and MRI negativity was associated with better PFS independently from ISS and FISH (p=0.0472). <h3>Conclusions</h3> To our knowledge, this is the first study evaluating PET/MRI for bone disease response in MM. Our data provide evidence that PET/MRI represents a promising tool for imaging MRD negativity evaluation, with patients being both PET and MRI negative showing improved PFS.