Flow cytometry has become a highly valuable method to monitor minimal residual disease (MRD) and evaluate the depth of complete response (CR) in bone marrow (BM) of multiple myeloma (MM) after therapy. However, current flow-MRD has lower sensitivity than molecular methods and lacks standardization. Here we report on a novel next generation flow (NGF) approach for highly sensitive and standardized MRD detection in MM. An optimized 2-tube 8-color antibody panel was constructed in five cycles of design-evaluation-redesign. In addition, a bulk-lysis procedure was established for acquisition of ⩾107 cells/sample, and novel software tools were constructed for automatic plasma cell gating. Multicenter evaluation of 110 follow-up BM from MM patients in very good partial response (VGPR) or CR showed a higher sensitivity for NGF-MRD vs conventional 8-color flow-MRD -MRD-positive rate of 47 vs 34% (P=0.003)-. Thus, 25% of patients classified as MRD-negative by conventional 8-color flow were MRD-positive by NGF, translating into a significantly longer progression-free survival for MRD-negative vs MRD-positive CR patients by NGF (75% progression-free survival not reached vs 7 months; P=0.02). This study establishes EuroFlow-based NGF as a highly sensitive, fully standardized approach for MRD detection in MM which overcomes the major limitations of conventional flow-MRD methods and is ready for implementation in routine diagnostics.

IntroductionTreatment of patients with multiple myeloma (MM) is disappointing. In this regard, the Southwest Oncology Group (SWOG) experience on standard dose therapy in 7 consecutive, large phase 3 studies has shown median survival times of less than 3 years, irrespective of the treatment given. 1 In addition, the Programa para el Estudio de la Terapéutica en Hemopatía Maligna (PETHEMA) group found that increased doses of conventional chemotherapy did not result in significant prolongation of survival. 2 Finally, meta-analysis of 6633 patients from 27 randomized trials failed to show any superiority of combination chemotherapy over melphalan/ prednisone in terms of duration of response and survival. 3 Furthermore, the Nordic Myeloma Study Group reported no survival improvement in conventionally treated younger patients with myeloma in the past 2 decades. 4 These limitations led to the current tendency to offer high-dose therapy (HDT)/stem cell support to MM patients as part of the frontline treatment. 5 Two randomized trials conducted by the Intergroup Français du Myeloma (IFM) and the Medical Research Council (MRC) showed that HDT significantly increased complete remission (CR), event-free survival (EFS), and overall survival (OS) compared with conventional chemotherapy. 5,6 However, 2 other randomized trials, reported in abstract form, failed to show any superiority of autologous J.B. and J.S.M. created the initial concept/design of the trial, analyzed and interpreted the data, wrote the manuscript, modified subsequent drafts, and finalized the manuscript; L.R. and A. Sureda contributed to analysis and interpretation of the data and to drafting the manuscript; J.B., J.S.M., L.R., and A. Sureda brought a significant number of patients to the study; M.F. participated in the analysis of the data and in the updating process throughout the study period; and J.M.R., J.D.-M., J.G.-L., M.V.M., L.P., J.F.-C, J.M.M., P.G., F.C., M.C., J.T., S.G., M.J.M., A.B., A. Soler, and L.F. participated in the conception/design of the study, included patients, provided the PETHEMA database with the patient data and periodic updating, and actively discussed the progress of the trial at the annual PETHEMA meetings. All the authors are members of PETHEMA and reviewed and approval the final version of the manuscript.An Inside Blood analysis of this article appears in the front of this issue.Reprints: Joan Bladé , Hematology Department, Hospital Clínic, Villarroel 170, 08036 Barcelona, Spain; e-mail: jblade@clinic.ub.es.The publication costs of this article were defrayed in part by page charge payment. Therefore, and solely to indicate this fact, this article is hereby marked ''advertisement'' in accordance with 18 U.S.C. section 1734. For personal use only. on March 22, 2019. by guest www.bloodjournal.org From transplantation. 7,8 The objective of the present study was to investigate, in a prospective randomized trial, the efficacy of HDT intensification therapy compared with continuation with conventional chemotherapy in patients wit...

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