High-Dose Melphalan Plus Thiotepa as Conditioning Regimen before Second Autologous Stem Cell Transplantation for “De Novo” Multiple Myeloma Patients: A Phase II Study

High-dose melphalan (MEL) is the standard therapy for autologous stem cell transplantation (ASCT) in multiple myeloma (MM), although the optimal conditioning regimen remains yet to be identified. Thiotepa (THIO) appears to be a potentially effective option, with broad-spectrum antitumor efficacy that can be added to myeloablative multiagent regimens for ASCT in hematopoietic tumors. We conducted a phase II trial, adding THIO (275 mg/m2) to high-dose MEL (140 mg/m2) before a second ASCT, in a tandem ASCT strategy, in 64 patients with “de novo” MM. Overall, there was no transplant-related mortality. The incidence of neutropenic fever and mucositis (grades 3 to 4) was 39% and 9%, respectively. Median number of days to neutrophil and platelet engraftment were 11 and 12, respectively. After the second transplantation, the complete response improved to 43.8%. Overall response rate was 86%. After a median follow-up of 18.1 months, 13 patients had progressed and 3 died from MM. Median progression-free survival was not reached, and actuarial 2-year rates of progression-free and overall survival were 71% and 88.9%, respectively. Our results suggest that THIO/MEL is a feasible and safe conditioning regimen for ASCT in MM and should be explored for efficacy in a phase III study.