C005 | PROSPECTIVE FUNCTIONAL BONE DISEASE EVALUATION OF NEWLY-DIAGNOSED MULTIPLE MYELOMA WITH COMBINED USE OF 18F-FDG-PET/CT AND WHOLE-BODY DIFFUSION-WEIGHTED MAGNETIC RESONANCE AT STAGING AND RESPONSE ASSESSMENT

Background: FDG-PET/CT is the most widely used imaging technique to detect bone and extramedullary disease (EMD) in multiple myeloma (MM) and is recommended for response assessment by IMWG. Whole-body diffusion-weighted MRI (WB-DW-MRI) has emerged as high-sensitivity technique. Aims: We present a prospective single-center study aimed at comparing PET/CT and WB-DW-MRI during diagnosis/staging of smoldering MM (SMM) and newly diagnosed MM (NDMM) and in defining treatment response, in association with minimal residual disease (MRD) assessment. Methods: Patients (pts) undergo PET/CT and WB-DW-MRI at baseline (B); positive techniques are repeated before maintenance therapy (transplant-eligible pts) or after 1 year of therapy (transplant-ineligible pts). Interpretation of the 2 techniques is based on IMPeTUs and MY-RADS guidelines. Pts achieving ≥very good partial response (VGPR) undergo MRD assessment by Next Generation Sequencing (NGS). Results: Between October 2022 and March 2025, 205 pts (74 SMM,131 NDMM) were enrolled. Among NDMM pts with CT-assessed bone disease (64%), MRI was positive in 100% and PET in 89%; in the remaining 36% pts, MRI was negative in 49% (none with PET-assessed focal lesions, FLs) and positive in 51%. MRI detected FLs and paraskeletal disease (PSD) in more NDMM pts than PET (FLs: 76% vs 57%, p=0.001; PSD: 30% vs 23%, p=0.001); concordance was perfect in detecting EMD (2%, k=1) and slight in detecting diffuse disease (DD)(24% vs 34%, p=0.001, k=0.4). By WB-DW-MRI, DD was related to higher % of bone marrow plasma cells (p=0.002), lower Hb (p=0.002), higher concentration of M protein in serum (p=0.02) and urines (p=0.01), whereas presence of >3 FLs was related to R-ISS 3 (p=0.001) and lower Hb (p=0.02). Among SMM pts, PET detected DD in more pts than MRI (8% vs 5%, p=0.04) with slight concordance (k=0.4) whereas FLs detected were similar (5% vs 8%, p=0.8). To April 2025, 48 pts reached the re-evaluation phase: among 31pts repeating both techniques, a concordance of 93% (k=0.6) was observed. Among 27 pts achieving ≥VGPR and imaging response by both techniques, MRD assessment by NGS was available for 13 pts (48%), resulting negative in 8 (62%) and positive in 5 (38%). Conclusion: Our data support combined use of PET/CT and WB-DW-MRI for MM staging at B; preliminary data also show a good concordance in response assessment. Updated data with extended follow-up and regarding imaging response and MRD assessment will be presented at the meeting.