• Mauricio Burotto, Maryalice Stetler-Stevenson, Evgeny Arons, Hong Zhou, Wyndham Wilson, and Robert J Kreitman.
• Authors' Affiliations: Laboratories of Molecular Biology and Pathology, and Metabolism Branch, National Cancer Institute, NIH, Bethesda, Maryland.
• Clin Cancer Res. 2013 Nov 15; 19 (22): 6313-21.

PurposeTo determine tolerability and for the first time explore efficacy of bendamustine-rituximab (BR) in multiply relapsed/refractory hairy cell leukemia (HCL), using two different dose levels of bendamustine.Experimental DesignPatients with HCL with ≥2 prior therapies requiring treatment received rituximab 375 mg/m(2) days 1 and 15 plus bendamustine 70 (n = 6) or 90 (n = 6) mg/m(2), days 1 and 2, for six cycles at 4-week intervals.ResultsAt 70 and 90 mg/m(2)/dose of bendamustine, overall response rate was 100%, with three (50%) and four (67%) complete remissions (CR) in each respective group. Minimal residual disease (MRD) was absent in 67% and 100% of CRs, respectively. All six without MRD remain in CR at 30 to 35 (median, 31) months of follow-up. Soluble CD22 and CD25 levels decreased with all responses, with median values decreasing from 17.7 and 42 ng/mL at baseline to undetectable and 2 ng/mL after CR, respectively (P < 0.001). Of 12 patients receiving 72 cycles of BR, the most common toxicities were hematologic, including thrombocytopenia (83%), lymphopenia (75%), leukopenia (58%), and neutropenia (42%). Grade III and IV hematologic toxicity included lymphopenia and thrombocytopenia (each 75%), leukopenia (58%), and neutropenia (25%). No significant dose-related differences were detected in response or toxicity.ConclusionBR has significant activity in HCL. Bendamustine at either 70 or 90 mg/m(2)/dose was highly effective in multiply relapsed/refractory HCL and could be considered for achieving durable CRs without MRD in patients after failure of standard therapies. As it was not dose-limiting, 90 mg/m(2)/dose was chosen for future testing.©2013 AACR.

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