Busulfan plus melphalan versus high-dose melphalan as a conditioning regimen for autologous stem cell transplantation in multiple myeloma with high-risk features (KMM 2015).

Despite the development of effective agents for multiple myeloma (MM), the management of patients with high-risk MM (HRMM) is challenging. High-dose treatment followed by autologous stem cell transplantation (ASCT) is regarded as upfront treatment for transplant-eligible patients with HRMM. In the present study, we retrospectively investigated the efficacies of two conditioning regimens for upfront ASCT in newly diagnosed patients with MM and high-risk features: high-dose melphalan (HDMEL; 200 mg/m2) and busulfan plus melphalan (BUMEL). In total, 221 patients underwent ASCT between May 2005 and June 2021; among these 221 patients, 79 had high-risk cytogenetic abnormalities. In patients with high-risk cytogenetics, BUMEL showed a tendency toward longer overall survival (OS) and progression-free survival (PFS) compared to HDMEL (median OS; not reached vs. 53.2 months; P = 0.091, median PFS; not reached vs. 31.7 months; P = 0.062). Additionally, multivariate analysis revealed that BUMEL was significantly associated with PFS (hazard ratio = 0.37, 95% confidence interval = 0.15-0.89, P = 0.026). We compared BUMEL with HDMEL in patients with other high-risk features, such as high lactate dehydrogenase level, extramedullary disease, and poor response to frontline therapy. Notably, among patients with less than very good partial response (VGPR) to frontline therapy, median PFS was significantly longer in the BUMEL group than in the HDMEL group (55.1 vs. 17.3 months, respectively; P = 0.011). These findings indicate that BUMEL may be an effective conditioning regimen for upfront ASCT in MM patients with high-risk cytogenetics; BUMEL may be more appropriate than HDMEL for patients with less than VGPR to frontline therapy.