A Phase I/II Study of Escalating Doses of Bortezomib in Conjunction with High-Dose Melphalan as a Conditioning Regimen for Salvage Autologous Peripheral Blood Stem Cell Transplantation in Patients with Multiple Myeloma

Escalating doses of bortezomib with high-dose melphalan was evaluated as as a conditioning regimen for autologous stem cell transplantation (ASCT) in patients with relapsed or refractory multiple myeloma (MM). MM patients with less than a partial remission (PR) (or 50% reduction) compared to their pretransplantation paraprotein parameters after a prior ASCT with melphalan conditioning, or who were in relapse after a prior autologous transplantation, were eligible for study. Bortezomib was dose escalated in steps of 1, 1.3, and 1.6 mg/m² (3 × 3 design) on days -4 and -1 before transplantation with melphalan 200 mg/m² given on day -2. Thirty-two patients were enrolled: 12 in the phase I dose escalation phase and an additional 20 in phase II to gain additional experience with the regimen. Twenty-four (75%) patients were Durie Salmon stage III, and 12 (37.5%) had >2 prior lines of therapy. The overall response rate (≥PR) was 44% with 22% complete remission. Two-year overall survival and progression-free survival were 76% and 39%, respectively, with a median follow-up of 31.7 months. The most common grade 3 and 4 nonhematologic adverse events were neutropenic fever (25%), nausea (18.8%), and mucositis (9.4%). Serious adverse events included intensive care unit admission (9.4%), seizure (3.1%), prolonged diarrhea (3.1%), and Guillain-Barre syndrome (3.1%). Two patients (6%) died of sepsis. There was no emergent peripheral neuropathy nor increase in any pre-existing peripheral neuropathy. The addition of bortezomib to melphalan as conditioning for salvage ASCT was well tolerated. More importantly, it can provide durable remission for patients who have a suboptimal response to prior single-agent melphalan conditioning for ASCT, without requiring a reduction in the dose of melphalan. Larger randomized prospective studies to determine the effect of combination conditioning are being conducted.