Upfront or Deferred Autologous Stem Cell Transplantation for Newly Diagnosed Multiple Myeloma in the Era of Triplet and Quadruplet Induction and Minimal Residual Disease/Risk-Adapted Therapy

Simple Summary Patients who are diagnosed with multiple myeloma are given an initial sequence of treatments that usually, for those who are young and fit enough, includes high-dose melphalan followed by autologous stem cell transplantation. This has contributed to the improvement in survival seen over the past 30 years. However, high-dose melphalan has significant limitations, including short-term side effects and longer-term issues such as an increased risk of developing secondary hematologic malignancies including leukemia. There are now numerous highly efficacious combination regimens for initial treatment that result in increasingly large proportions of patients achieving deep responses with no evidence of minimal residual disease. Moreover, large, randomized studies using these regimens have shown no benefit in overall survival after receiving high-dose melphalan with stem cell transplantation. There is thus a growing rationale for selected eligible patients to defer receiving high-dose melphalan and stem cell transplantation until potentially needed in a subsequent line of treatment.Abstract The standards of care for the initial treatment of patients with newly diagnosed multiple myeloma (NDMM) who are eligible for high-dose melphalan and autologous stem cell transplantation (HDM-ASCT) include highly active triplet and quadruplet regimens based on proteasome inhibitors, immunomodulatory drugs, and monoclonal antibodies. These regimens are resulting in improved outcomes and increasingly high rates of minimal residual disease (MRD)-negative responses without HDM-ASCT as part of the upfront therapy. Furthermore, recent randomized studies have shown that, while transplant-based approaches as a frontline therapy result in significantly longer progression-free survival compared to non-transplant approaches, this has not translated into an overall survival benefit. Given these developments, and in the context of the treatment burden of undergoing HDM-ASCT, in addition to the acute toxicities and long-term sequelae of HDM, which are associated with the genotoxicity of melphalan, there is an increasing rationale for considering deferring upfront HDM-ASCT in select transplant-eligible patients and saving it as a treatment option for later salvage therapy. Here, we review the latest clinical trial data on upfront or deferred HDM-ASCT and on the activity of quadruplet induction regimens, including rates of MRD-negative responses, and summarize emerging treatment approaches in the upfront setting such as the use of MRD-directed therapy and alternatives to HDM-ASCT.