Prognostic value of simultaneous [ ¹⁸ F]FDG‐PET/MRI in refractory multiple myeloma treated with anti‐BCMA CAR T

Abstract

The aims of this study were to assess the prognostic value for progression‐free survival (PFS) and the diagnostic value (detection rate of multiple myeloma [MM]–related medullary and extra‐medullary disease) of whole‐body simultaneous [ ¹⁸ F]fluorodeoxyglucose‐positron emission tomography coupled with magnetic resonance imaging (WB[ ¹⁸ F]FDG‐PET/MRI) performed before and after idecabtagene‐vicleucel (ide‐cel) therapy in patients with triple‐class (or more) relapsed/refractory multiple myeloma (RRMM). A total of 73 patients were prospectively enrolled in this monocentric cohort, and 72 of them underwent WB[ ¹⁸ F]FDG‐PET/MRI imaging before ide‐cel (after personalized bridging therapy). Overall, active disease was detected in 64/72 patients (89%). Multivariate analyses showed that the presence of diffuse bone marrow involvement (BMI) pattern on PET (hazard ratio [HR]: 2.65; 95% CI: 1.16–6.1, P = 0.02) or MRI (HR: 2.69; 95% CI: 1.28–5.66, P = 0.009) was associated with shorter PFS. A total of 66 patients underwent [ ¹⁸ F]FDG‐PET/MRI for response to ide‐cel therapy assessment. Diffusion‐weighted MRI (DW‐MRI) detected residual disease (response assessment category [RAC]2 or higher according to MY‐RADS) in 9/66 patients (14%) and PET (no complete metabolic response according to Deauville score) in 7/66 patients (11%). Overall, [ ¹⁸ F]FDG‐PET/MRI increased residual disease detection to 13 of 66 patients (20%). Patients with residual disease on DW‐MRI (RAC2 or higher) had shorter PFS (HR: 4.11; 95% CI: 1.8–9.4; P < 10 ⁻³ ) than those without (RAC1). Achieving at least a partial metabolic response on PET significantly improved the PFS (P = 0.0046) as well. The combination of [ ¹⁸ F]FDG‐PET and DW‐MRI enabled the identification of three distinct risk groups, including a very high‐risk group defined by both MRI and PET positivity.