Conditioning regimens in autologous stem cell transplantation for multiple myeloma: a comparative study of efficacy and toxicity from the Spanish Registry for Transplantation in Multiple Myeloma.

High-dose chemoradiotherapy conditioning regimens for autologous stem cell transplantation (ASCT) are generally held to give similar results in multiple myeloma (MM), but no specific comparative study has been published. We addressed this issue by comparing the main high-dose chemoradiotherapy regimens used in the Spanish Registry. Patient cohorts included 315 cases treated with 200 mg/m2 melphalan (MEL200), 127 patients with 140 mg/m2 melphalan plus total body irradiation (MEL140 + TBI) and 121 cases with 12 mg/kg busulphan plus 140 mg/m2 melphalan (BUMEL). After ASCT, granulocyte and platelet recovery time was similar in all conditioning groups. There were no differences in transplant-related mortality. All regimens yielded a similar response in reference to pre-ASCT MM status, although BUMEL produced a slightly better overall response when compared with the other regimens (97% vs. 89% and 92%, P = 0.003). The 5-year overall survival (OS) with BUMEL was 47% [95% confidence interval (CI) 26-68] compared with 43% (CI 31-54) for MEL140 + TBI and 37% (CI: 18-56) for MEL200. The median survival for the BUMEL group was 64 months compared with 45 and 37 months for the MEL200 and MEL140 + TBI groups respectively. These differences were non-significant (P = 0.2). The median event-free survival (EFS) was better for BUMEL (32 months) than for MEL200 (22 months) or for MEL140 + TBI (20 months). The differences in EFS between BUMEL and the other conditioning regimens reached statistical significance (P = 0.01). Nevertheless, the adjusted multivariate analysis for OS and EFS revealed that the conditioning regimens had no independent prognostic value. We concluded that three different conditioning regimens, commonly used for ASCT in MM, have a similar antimyeloma effect. However, the trend for better results observed in our series with BUMEL requires a prospective trial.