Bendamustine in Patients with Quad- and Penta-Refractory Multiple Myeloma
Authors: Goldsmith Scott , Fiala Mark A. , Wang Brandon B. , Schroeder Mark A. , Wildes Tanya M. , Ghobadi Armin , Stockerl-Goldstein Keith E. , Vij Ravi 
Published: October 2019

Abstract
Introduction: Despite significant advances in multiple myeloma (MM) therapy, disease progression through multiple novel treatments is often inevitable. Quad-refractory MM (refractory to bortezomib, carfilzomib, lenalidomide, and pomalidomide), or penta-refractory MM (refractory to an anti-CD38 monoclonal antibody as well) portends a poor prognosis, with few subsequent lines of treatment currently available. We and others have used bendamustine combined with corticosteroids as a salvage regimen, but there is a paucity of outcomes data in this heavily pretreated population.
Methods: We conducted a retrospective study to identify all patients who received bendamustine with corticosteroids for quad- or penta-refractory MM at our institution between 2013 and 2018. Disease response and refractoriness were defined by IMWG criteria. The primary endpoint was overall response rate (ORR) defined as PR or better. Secondary endpoints included overall survival (OS) and duration of response (DOR).
Results: Twenty-seven patients were identified; 5 patients were quad-refractory, and 22 penta-refractory (Table 1). Twenty-two (81%) patients had at least one prior autologous stem cell transplant and 1 had a prior allogeneic. The median age at time of bendamustine was 61, 52% were female, and 85% were white. All patients received bendamustine at a dose of 90mg/m2 on days 1 and 2 of a 28 day cycle. Twelve patients (44%) received more than one cycle (range: 1-8). The overall response rate was 26%. While no patient achieved CR, 4 achieved VGPR and 3 a PR. Two of the 5 (40%) quad-refractory patients responded compared to 5 of the 22 (23%) penta-refractory. Sixteen (59%) were primary refractory to bendamustine and one patient went onto hospice prior to response evaluation. Overall the median PFS was 1.4 months (95% CI 1.1-1.6) and median OS was 8.7 months (95% CI 2.3-15.0). For responders (≥PR), median DOR was 6.6 months (95% CI 0.0-13.7) and median OS was 14.0 months (95% CI 0.6-27.4).
Conclusion: The prognosis of quad- and penta-refractory MM remains poor. In this heavily pre-treated population, bendamustine demonstrates a 26% ORR (95% CI 11%-46%). The DOR and OS of the patients was poor but highly heterogeneous. Those who did respond to bendamustine had notably improved OS. Given the limited available options for quad- and penta-refractory MM, bendamustine remains a reasonable salvage therapy. Prospective trials are warranted perhaps including additional agents that are effective in penta-refractory patients.

Disclosures
Schroeder: Amgen Inc.: Consultancy, Membership on an entity's Board of Directors or advisory committees. Vij:Celgene: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Bristol-Myers Squibb: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Jansson: Honoraria, Membership on an entity's Board of Directors or advisory committees; Amgen: Honoraria, Membership on an entity's Board of Directors or advisory committees; Jazz Pharmaceuticals: Honoraria, Membership on an entity's Board of Directors or advisory committees; Karyopharma: Honoraria, Membership on an entity's Board of Directors or advisory committees; Takeda: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding.