Outcomes of Patients with Heavily Pretreated Relapsed/Refractory Multiple Myeloma Receiving Salvage Cytotoxic Therapy with Supportive Stem Cell Boost

Background Multiple myeloma (MM) is an incurable hematologic malignancy characterized by the neoplastic proliferation of plasma cells, which produce monoclonal immunoglobulin that can cause vital organ damage, subsequently leading to significant morbidity and mortality. Autologous hematopoietic stem cell transplant (ASCT) is the standard-of-care management of eligible patients with newly diagnosed MM. Experts recommend collecting enough stem cells upfront to support a possible tandem transplant, salvage ASCT, or a stem cell "boost" to allow for the administration of multiagent cytotoxic chemotherapy in patients with relapsed/refractory disease.Objective There is currently a paucity of data on the response rates and outcomes of patients with relapsed MM who undergo cytotoxic chemotherapy followed by a stem cell boost; this study examines the outcomes of patients treated with this approach.Methods We conducted a retrospective chart review from two oncologic treatment centers in the United States of adult patients who underwent a first ASCT between 1999 and 2021 and subsequently received cytotoxic chemotherapy followed by stem cell boost further on in their disease course. Survival analysis was carried out using the Kaplan-Meier method, and the log-rank test was used to compare survival curves.Results We found that the majority (56.6%) of these patients responded to therapy and that 60.6% of these patients were able to receive at least one subsequent line of therapy post-boost. Furthermore, patients who responded to therapy had significantly longer median overall survival compared to those who did not respond (323 days vs 93 days, p=0.0045), and age did not affect response to therapy.Conclusion This data allow clinicians to appropriately implement and inform patients of the therapeutic uses and clinical outcomes of stem cell boost in patients with multiply relapsed/refractory MM.