Minimal Residual Disease Detection By Multiparametric Flow Cytometry in Newly Diagnosed Multiple Myeloma Patients: A Preliminary Analysis of the EMN02/HO95 MM Study

Introduction:

Multiple myeloma (MM) is still an incurable disease and patients may relapse despite achievement of complete remission (CR). Minimal residual disease (MRD) assessment by multiparameter flow cytometry (MFC) on bone marrow (BM) is a sensitive diagnostic tool to measure response and is  highly predictive of outcome in MM as previously reported. The aim of this study is to evaluate the role of MRD monitoring by MFC in MM patients receiving novel agents with or without autologous stem cell transplantation (ASCT) and to investigate the efficacy of treatments by using MRD-negativity as a deeper response criteria.

Methods: The RV-MM-COOP-0556 (EMN02/HO95 MM) study is a phase III, randomized, trial including newly diagnosed MM patients ≤ 65 years. All subjects received 4 cycles of Bortezomib-Cyclophosphamide-Dexamethasone (VCD) induction, followed by Cyclophosphamide chemotherapy and subsequent stem cell mobilization and collection. Afterward, patients were randomized to receive 4 cycles of Bortezomib-Melphalan-Prednisone (VMP) vs one or two cycles of High-Dose-Melphalan (HDM) followed by ASCT. After intensification patients were secondly randomized to receive two cycles of consolidation with Bortezomib-Lenalidomide-Dexamethasone (VRD) vs no consolidation, followed by Lenalidomide maintenance in both arms. Patients who achieved CR/sCR according to IMWG criteria (Rajkumar et al. Blood 2011) after intensification/consolidation treatment, were eligible for the MRD sub-study. MRD analysis by MFC was performed on BM samples after intensification/consolidation, after 6 courses of maintenance, and thereafter every 6 months until progression, to detect monoclonal plasma cells (PCs). Here, we used a double antibody combination (CD138Fitc/CD20PerCp-Cy5.5/CD117APC/CD45APC-H7/CD38PE-Cy7; cyKappaFitc/cyLambdaPE/CD19PerCp-Cy5.5/CD56APC/CD45APC-H7/CD38 PE-Cy7): one tube was employed to obtain PCs quantification, the other one to validate PCs clonality. MRD-negativity was defined when <20 clonal PCs were detected among ≥2.000.000 leukocytes (<0.001%).

Results: One hundred-eleven Italian patients (58 male/53 female) with a median age of 56 years (IQR 52-62) entered MRD sub-study. Sixteen (14%) were ISS stage III, 24 (22%) had high-risk cytogenetic profile and 10 (9%) had LDH levels higher than the upper normal limit.

Forty-five patients (40%) received VMP as intensification and 66 (60%) underwent ASCT,  thereafter 65 (58%) received VRD consolidation, 24 after VMP and 41 after ASCT. The median follow-up were 28.7 and 17 months from starting treatment and from MRD enrollment, respectively. After intensification/consolidation, 4 patients were not evaluable for MRD due to  unsuitable samples, MRD negativity rate was 79% (85 out of 107 evaluable patients) and was independent from the intensification therapy: actually 50/63 patients who received ASCT and 35/44 patients who received VMP achieved MRD negativity. Within MRD-negative patients, 48/85 (56%) received VRD consolidation without major differences between VMP and ASCT. With the limitation related to the shorter follow-up, depth of response further improved during maintenance: 11/22 (50%) of MRD-positive patients became MRD-negative, independently from previous intensification therapy. 

Conclusions: MRD detection by MFC is a feasible technique in MM and allows to detect residual tumor cells among CR and sCR patients. Preliminary MRD results show that, in patients achieving CR, intensification with VMP or ASCT induced comparable rates of MRD-negativity and maintenance with Lenalidomide further improved depth of response in both arms. Longer follow-up is needed to correlate MRD status to prognosis and clinical outcome and to evaluate the role of maintenance therapy in increasing the quality of response.