Sustained Residual Disease Negativity Assessed By Diffusion-Weighted Whole-Body MRI (DW-MRI) Has Strong Predictive Relevance for Survival in Newly Diagnosed Multiple Myeloma Patients on Maintenance Therapy after Autologous Stem Cell Transplantation (ASCT)

Introduction: The role of minimal residual disease (MRD) in Multiple Myeloma (MM) as a surrogate biomarker of patients' outcome, as well as the prognostic information of functional imaging response after treatment have been established in recent years. Furthermore, the predictive relevance of sustained MRD negativity assessed by marrow and imaging techniques and its association with an excellent outcome is emerging in clinical trials. Diffusion-weighted whole-body MRI (DW-MRI) is increasingly used in the management of MM patients, but data regarding the predictive role of sustained DW-MRI response after treatment are lacking. The Myeloma Response Assessment and Diagnosis System (MY-RADS) recommendations have established criteria for Response Assessment Category (RAC) (Messiou C et al, Radiology 2019) with a 5 point scale defining the probability of complete imaging response (i.e. RAC 1) or progressive disease after treatment (i.e. RAC 5). We implemented the RAC criteria in our clinical practice and DW-MRI at 1-year in MM patients treated with autologous stem cell transplantation (ASCT) followed by maintenance therapy.

Patients and methods: We retrospectively analyzed the outcome of 57 newly diagnosed MM patients (median age 61 years) diagnosed at our institution from January 2015 to December 2019 receiving maintenance therapy after ASCT. Patients underwent DW-MRI evaluation according to MY-RADS criteria at day +100 after ASCT, before maintenance, and after 1 year with the aim of monitoring imaging residual disease. Bone marrow samples were collected for MRD assessment by 8-color FCM (sensitivity 10-5) at day +100 after ASCT, before maintenance, and after 1 year. We focused on sustained 1-year DW-MRI negativity evaluated according to RAC response, and its potential predictive role at that timepoint on progression free survival (PFS) and overall survival (OS). In patients with available 1-year MRD evaluations, concordance between 1-year MRD and DW-MRI results was calculated and the level of agreement was expressed by Cohen's kappa statistics.

Results: Out of 57 patients, 23 (40%) were ISS stage 3 and 14 (25%) showed high risk cytogenetics. Patients were treated with the following induction regimens: VTD 42, VRD 5, Dara-VRD 6, KRD 3, KCD 1. Single ASCT with MEL200 conditioning was performed in 33 patients (58%), whereas 24 patients (42%) received double ASCT. Subsequent maintenance was performed with lenalidomide (49 patients, 86%) or daratumumab-lenalidomide (8 patients, 14%). Response rates after ASCT were PR 9%, VGPR 23%, CR 51% and sCR 17%. According to MY-RADS, a complete imaging response (RAC1) at day +100 after ASCT was observed in 34 patients (60%). Sustained 1 year complete imaging response during maintenance therapy was observed in 43 patients (75%). Some residual disease was identified at that timepoint in 14 patients (25%) [RAC 2: 6 (11%), RAC > 2: 8 (14%)]. After a median follow up of 36 months, PFS and OS were significantly longer in patients with sustained 1-year imaging negativity, compared to patients with imaging residual disease (RAC 1 vs RAC ≥2): median PFS 56 vs 24,1 months, p <0,0001, HR 0,11 (95% CI: 0,030-0,382); median OS NR vs 40,5 months, p < 0,0001, HR 0,05 (95% CI: 0,006-0,364). MRD at 1-year timepoint was available in 30 patients and was negative in 28 (93%) cases. Concordance between 1-year DW-MRI and MRD results was high (97%, kappa 0,783: 7% both positive, 90% both negative).

Conclusion: Our real-life data analysis confirms the predictive value of imaging residual disease assessment with DW-MRI after ASCT and highlights the importance of achieving sustained imaging MRD negativity during maintenance therapy regardless of different treatment strategies. Moreover, given the high rates of CR seen in patients with MM with novel effective treatment combinations, the detection of residual disease with the combined evaluation of marrow and functional imaging techniques during maintenance therapy can help the physician to identify patients with increased risk of early relapse and particularly poor prognosis. Our preliminary data regarding the high concordance observed between DW-MRI and MRD results during maintenance therapy suggest that DW-MRI could represent a reliable non-invasive technique to monitor residual disease.