What Is the Frequency of Transplant-Eligible Multiple Myeloma Patients Being Cured? the Impact of an MGUS-like Signature at Diagnosis and MRD-Negativity

Introduction: Although multiple myeloma (MM) is typically described as an incurable disease, it has been shown in recent years that a small fraction of patients may reach more than 10-years progression-free survival (PFS), which is considered as the minimum threshold to identify patients in "operational cure". However, because of the scarcity of available data there is significant lack of knowledge in MM regarding the frequency of cases attaining operational cure, nor the existence of biomarkers that could prospectively predict such curability.

Methods: Herein, we sought to define the frequency as well as the biomarkers predictive of operational cure in a large series of uniformly-treated transplant-eligible patients enrolled in the PETHEMA/GEM2000 protocol (VBMCP/VBAD followed by HDT/ASCT and 2 years of maintenance with interferon and prednisone). Patients' follow-up was updated at the time of abstract submission, and the median follow-up of the series is now of 12-years. We used an automated multiparameter flow cytometric (MFC) classification model focused on the analysis of the bone marrow plasma-cell compartment to identify among newly diagnosed symptomatic MM those with MGUS-like vs. MM-like phenotypic signatures. Minimal residual disease (MRD) was monitored using a first-generation 4-color MFC assay (CD38-FITC / CD56-PE / CD19-PerCPCy5.5 / CD45-APC) with a limit of detection of 10^-4. PFS and overall survival (OS) were measured from the time of diagnosis.

Results: From a total of 1075 patients enrolled in the GEM2000 protocol, 763 were eligible for this analysis because they either relapsed or died during the first 10-years from diagnosis (n=666; 87%), or remained progression-free and alive for more than 10-yers (n=97; 13%); accordingly, all patients remaining progression-free and alive but for which the follow-up was inferior to 10-years were excluded from the analysis. We then investigated the biomarkers that could help to identify patients reaching operational cure after HDT/ASCT. As compared to the vast majority of cases, patients reaching >10-years PFS (13%) had significantly less frequent anemia (76% vs. 60%, respectively; P=.002), as well as more frequent Durie-Salmon stage IA (14% vs. 6%; P=.004), MGUS-like signature as determined by the automated MFC algorithm (28% vs. 6%; P<.001), complete response (CR) after HDT/ASCT (51% vs. 35%; P=.003), and MRD-negativity by MFC (72% vs. 31%; P<.001). Other biomarkers such as ISS, LDH, ploidy and proliferation were not significantly different among patients reaching >10-years PFS vs. those who relapsed earlier. On multivariate analysis, only the presence of an MGUS-like signature at baseline (P=.04; HR: 3.9) and MRD-negativity at day+100 after HDT/ASCT (P=.006; HR: 6.3) emerged as independent predictive markers for >10-years PFS; anemia, Durie-Salmon and CR status were not retained in the logistic regression model. Accordingly, patients with an MFC-defined baseline MGUS-like signature reaching MRD-negativity after HDT/ASCT (n=14) had a median PFS of 10-years and a 10-year OS rate of 79%, which were significantly superior to those observed among cases with MM-like signatures being MRD-negative (n=54) or positive (n=99) after therapy [median PFS of 6 and 3 years (P<.001); 10-year overall survival rates of 55% and 19% (P<.001)].

Conclusions: We demonstrated that operational cure (i.e.: >10-years PFS) was possible for 13% of transplant-eligible MM patients before the era of novel agents. Curability rates were particularly frequent among patients with a benign phenotypic signature at diagnosis and MRD negativity after HDT/ASCT, suggesting a remarkable clinical benefit of attaining deep remissions after intensive treatment for patients with early MM.