Minimal Residual Disease Status in Multiple Myeloma 1 Year After Autologous Hematopoietic Cell Transplantation and Lenalidomide Maintenance Are Associated With Long-Term Overall Survival

PURPOSE Prognostic Immunophenotyping in Myeloma Response (PRIMeR) is an ancillary study of minimal residual disease (MRD) assessment for multiple myeloma by next-generation multiparameter flow cytometry (MFC). Patients were enrolled on a three-arm randomized control trial (Blood and Marrow Transplants Clinical Trials Network 0702 Stem Cell Transplant for Myeloma in Combination of Novel Agents [STaMINA]; ClinicalTrials.gov identifier: NCT01109004 ). METHODS Four hundred and thirty-five patients consented to the MRD panel, which included 10 monoclonal antibodies measured via six-color MFC. MRD was measured at baseline/preautologous hematopoietic cell transplant (BL/preAutoHCT), premaintenance (PM), and 1 year (Y1) after AutoHCT with a sensitivity of 10 –5 to 10 –6 . The primary objective was to assess MRD-negative (MRD neg ) at 1 year after AutoHCT and progression-free survival and overall survival (PFS/OS). RESULTS Similar to the STaMINA results, at a median follow-up of 70 months, there was no significant difference in PFS/OS by treatment arm in the PRIMeR patients. MRD neg at all three time points was associated with significantly improved PFS, and MRD neg at Y1 had significantly longer OS. Multivariate analysis of PFS, adjusting for disease risk and treatment arm, demonstrated hazard ratios (HRs) in MRD-positive patients compared with MRD neg patients at BL, PM, and Y1 of 1.55 ( P = .0074), 1.83 ( P = .0007), and 3.61 ( P < .0001), respectively. Corresponding HRs for OS were 1.19 ( P = .48), 0.88 ( P = .68), and 3.36 ( P < .001). Patients with sustained MRD neg or who converted to MRD neg by Y1 had similar PFS/OS. CONCLUSION To our knowledge, this first, prospective US cooperative group, multicenter study demonstrates that MRD neg at Y1 after AutoHCT with lenalidomide maintenance is prognostic for improved 6-year PFS and OS. Serial MRD measurements may direct trials to test how further therapy may improve long-term PFS and OS.