Busulfan/Cyclophosphamide Compared with Melphalan as a Conditioning Regimen for Autologous Transplantation of Multiple Myeloma: A Long-Term Assessment

Background: Melphalan was poorly available in mainland China. The aim of this study is to explore the dose-adjusted busulfan/cyclophosphamide (BU/CY) as an alternative regimen in auto stem cell transplantation (ASCT) for multiple myeloma (MM). Methods: A total of 105 newly diagnosed MM patients undergoing ASCT during May 2012 and August 2017 were retrospectively analyzed. The BU/CY regimen was applied to 64 patients. Busulfan (9.6 mg/kg or 8.0 mg/kg in total) and cyclophosphamide (3.6 g/m² or 3.0 g/m² in total) were administered according to the creatinine clearance rate (CCR). A high-dose melphalan (HDMEL) regimen (200 mg/m²) was given to the other 41 patients. Results: At a median follow-up of 65 (1~119) months, estimated overall survival (OS) and progression-free survival (PFS) at 104 months in the BU/CY and HDMEL groups were 35.6% vs. 20.5% (p = 0.263) and 20.2% vs. 2.4% (p = 0.035), respectively. The median overall survival (OS) and PFS of the HDMEL and BU/CY groups were 55 vs. 70.5 months and 26 vs. 46.5 months, respectively. In multivariate analysis, the BU/CY regimen was found to be the only protective factor for PFS. No lethal toxicity was found in the BU/CY group, and treatment-related mortality (TRM) in 100 days was similar to the HDMEL group. Conclusions: MM patients may also benefit from the dose-adjusted BU/CY regimen.