Few clinical studies have reported results of measurable residual disease (MRD) assessments performed as part of routine practice. Herein we present our single-institution experience assessing MRD in 234 multiple myeloma (MM) patients (newly diagnosed [NDMM = 159] and relapsed [RRMM = 75]). We describe the impact of depth, duration, and direction of response on prognosis. MRD assessments were performed by next-generation sequencing of immunoglobulin genes with a sensitivity of 10−6. Those achieving MRD negativity at 10−6, as well as 10−5, had superior median progression-free survival (PFS). In the NDMM cohort, 40% of the patients achieved MRD negativity at 10−6 and 59% at 10−5. Median PFS in the NDMM cohort was superior in those achieving MRD at 10−5 vs <10−5 (PFS: 87 months vs 32 months; P < .001). In the RRMM cohort, 36% achieved MRD negativity at 10−6 and 47% at 10−5. Median PFS was superior for the RRMM achieving MRD at 10−5 vs <10−5 (PFS: 42 months vs 17 months; P < .01). Serial MRD monitoring identified 3 categories of NDMM patients: (A) patients with ≥3 MRD 10−6 negative samples, (B) patients with detectable but continuously declining clonal numbers, and (C) patients with stable or increasing clonal number (≥1 log). PFS was superior in groups A and B vs C (median PFS not reached [NR], NR, 55 respectively; P < .001). This retrospective evaluation of MRD used as part of clinical care validates MRD as an important prognostic marker in NDMM and RRMM and supports its use as an endpoint in future clinical trials as well as for clinical decision making.

Background Stringent complete response (sCR) is used as a deeper response category than complete response (CR) in multiple myeloma (MM) but may be of limited value in the era of minimal residual disease (MRD) testing. Methods Here, we used 4-colour multiparametric flow cytometry (MFC) or next-generation sequencing (NGS) of immunoglobulin genes to analyse and compare the prognostic impact of sCR and MRD monitoring. We included 193 treated patients in two institutions achieving CR, for which both bone marrow aspirates and biopsies were available. Results We found that neither the serum free light chain ratio, clonality by immunohistochemistry (IHC) nor plasma cell bone marrow infiltration identified CR patients at distinct risk. Patients with sCR had slightly longer progression-free survival. Nevertheless, persistent clonal bone marrow disease was detectable using MFC or NGS and was associated with significantly inferior outcomes compared with MRD-negative cases. Conclusion Our results confirm that sCR does not predict a different outcome and indicate that more sensitive techniques are able to identify patients with differing prognoses. We suggest that MRD categories should be implemented over sCR for the future classification of MM responses.

The assessment of measurable residual disease (MRD) in bone marrow has proven of prognostic relevance in patients with multiple myeloma (MM). Nevertheless, and unlike other hematologic malignancies, the use of MRD results to make clinical decisions in MM has been underexplored to date. In this retrospective study, we present the results from a multinational and multicenter series of 400 patients with MRD monitoring during front-line therapy with the aim of exploring how clinical decisions made based on those MRD results affected outcomes. As expected, achievement of MRD negativity at any point was associated with improved PFS versus persistent MRD positivity (median PFS 104 vs. 45 months, p < 0.0001). In addition, however, 67 out of 400 patients underwent a clinical decision (treatment discontinuation, intensification or initiation of a new therapy) based on MRD results. Those patients in whom a treatment change was made showed a prolonged PFS in comparison with those 333 patients in which MRD results were not acted upon (respectively, mPFS 104 vs. 62 months, p = 0.005). In patients who achieved MRD negativity during maintenance (n = 186) on at least one occasion, stopping therapy in 24 patients vs. continuing in 162 did not alter PFS (mPFS 120 months vs. 82 months, p = 0.1). Most importantly, however, in patients with a positive MRD during maintenance (n = 214), a clinical decision (either intensification or change of therapy) (n = 43) resulted in better PFS compared to patients in whom no adjustment was made (n = 171) (mPFS NA vs. 39 months, p = 0.02). Interestingly, there were no significant differences when MRD was assessed by flow cytometry or by next-generation sequencing. Herein, we find that MRD is useful in guiding clinical decisions during initial therapy and has a positive impact on PFS in MM patients. This potentially opens a new dimension for the use of MRD in MM, but this role still remains to be confirmed in prospective, randomized clinical trials.

Lenalidomide is an immunomodulatory drug approved for maintenance treatment in newly diagnosed multiple myeloma, and it has been shown to improve progression-free survival (PFS) and, in several studies, overall survival. Nevertheless, the impact of prolonged treatment with lenalidomide on the kinetics of minimal residual disease (MRD) and its prognostic impact have not been studied in depth. To obtain better knowledge in this regard, we retrospectively analyzed 139 patients who received lenalidomide maintenance in real-world clinical practice and whose MRD levels were observed during the treatment period by multiparametric flow cytometry or next-generation sequencing with a sensitivity of at least 10−4. Lenalidomide maintenance correlated with an increased depth of the disease response, with 38.1% of patients achieving maximal response during maintenance. Moreover, 34.3% of patients who were MRD positive after induction treatment achieved MRD-negative status during maintenance and ultimately had improved PFS. Sequential MRD assessments identified patients with progressively decreasing MRD levels who also had better PFS outcomes, compared with patients not showing a decreasing pattern of MRD. These results support the role of maintenance therapy, not only to sustain, but also to increase the depth of disease response with a PFS benefit. In addition, MRD monitoring during maintenance identifies patients with better prognosis and may help in their clinical management.