Updated Outcomes of Fludarabine/Melphalan/Bortezomib (Flu/Mel/Vel) Conditioning for Upfront Allogeneic Hematopoietic Cell Transplantation in Multiple Myeloma

Background:

Multiple myeloma remains incurable despite impressive array of available novel agents and therapeutic strategies. Allogeneic hematopoietic cell transplantation (HCT) remains the only potentially curative option for patients with multiple myeloma but it is limited by its toxicities. We previously reported initial result of a phase 2 study of upfront allogeneic HCT in myeloma patients achieving at least very good partial response (VGPR) after initial therapy (Nishihori, et al. ASH 2013 abstract 3390) and here we report more mature results after a median follow up of 3 years.

Methods:

Twenty seven myeloma patients received allogeneic HCT between 01/2010 and 02/2015 at Moffitt Cancer Center (NCT 00948922). Eligible patients were age ≤ 60, achieving first ≥ VGPR or complete response (CR), and have 8/8 HLA-matched related or unrelated donors. Conditioning regimen consisted of fludarabine 30 mg/m² for 4 days (days -6, -5, -4, and -3) and melphalan 70 mg/m² for 2 days (days -4 and -3) followed by a single dose of bortezomib 1.3 mg/m² on day -3 (Flu/Mel/Vel regimen). GVHD prophylaxis was initially left to the discretion of physicians but later modified to only tacrolimus/methotrexate. No maintenance therapy was prescribed after allogeneic HCT.

Results:

The median age at transplant was 50 (range, 25-58) years. Disease status at the time of allogeneic HCT was VGPR (n=17: 63%) and CR/stringent CR (n=10: 37%). All patients received unmanipulated peripheral blood stem cell grafts from HLA-matched related donors (n=14) or HLA-matched unrelated donors (n=13). Graft-versus-host disease (GVHD) prophylaxis was tacrolimus plus either methotrexate (n=19: 70%), or mycophenolate mofetil (n=4), or sirolimus (n=4). All patients achieved neutrophil engraftment with a median of 15 (range, 11-19) days. Platelet engraftment was achieved with a median of 17 (range, 13 - 35) days and 2 patients did not recover platelets. The cumulative incidences of grades II-IV and grades III-IV acute GVHD at day 100 were 63.6% (95% confidence interval (CI): 43.1-81.1) and 19.6% (95%CI: 5.4-39.9), respectively. The cumulative incidence of moderate to severe chronic GVHD was 56.4% (95%CI: 36.3-75.5) at 1-year. The cumulative incidences of transplant-related mortality at day 100, 1 year and 2 years were 7.4% (95%CI: 0.8-20.0), 11.1% (95%CI: 2.7-25.4), and 11.1% (95%CI: 2.7-25.4), respectively. Progression-free survival estimates at 1, 2, and 3 years were 74.1% (95%CI: 53.2-86.7), 65.1% (95%CI: 43.3-80.2), and 65.1% (95%CI: 49.9-87.5), respectively. With a median follow up of 39 months for surviving patients, overall survival estimates at 1, 2 and 3 years were 85% (95%CI: 64.9-94.1), 75.4% (95%CI: 52.6-88.3), and 69.1% (95%CI: 53.8-93.5), respectively.

Conclusions:

The results of the this phase 2 trial of upfront allogeneic HCT with fludarabine/melphalan/bortezomib (Flu/Mel/Vel) conditioning are promising and provide the rationale for reasonable potentially curative option to younger and fit patients who are eligible for upfront intensive consolidation strategy. This approach may be potentially valuable for those with high-risk myeloma and a multicenter study is currently being conducted (BMT CTN protocol 1302:NCT02440464).