• Naoto Imoto, Daisuke Koyama, Isamu Sugiura, and Shingo Kurahashi.
• Division of Hematology and Oncology, Toyohashi Municipal Hospital, Aichi.
• Medicine (Baltimore). 2021 Feb 5; 100 (5): e24457e24457.

IntroductionHairy cell leukemia variant (HCL-v) is a rare lymphoproliferative disorder regarded as a splenic B-cell lymphoma/leukemia, unclassifiable tumor in the 2017 World Health Organization classification of lymphoid tumors. The prognosis of HCL-v is much worse than that of classical hairy cell leukemia and there is no consensus regarding the optimal treatment strategy for HCL-v. For patients with indolent lymphoma, rituximab plus bendamustine (RB) has proven effective in several clinical trials. Thus, RB is expected to be a treatment option for patients with HCL-v, but there have been few reports of its use in these patients.Patient ConcernsA 64-year-old man presented with leukocytosis and abnormal lymphocytes in peripheral blood in a medical examination. Computed tomography revealed mild splenomegaly, but no lymph node enlargement.DiagnosisThe patient was initially diagnosed with low-grade B-cell lymphoma. After he experienced a second relapse, his clinical data were reviewed again; subsequently, he was diagnosed with HCL-v on the basis of clinical presentation, flow cytometry findings, and cytogenetic abnormalities.InterventionsThe patient was first treated with the cyclophosphamide, doxorubicin, vincristine, and prednisone (CHOP) regimen. After the regimen was ineffective, he received six cycles of RB. After relapse, the patients received an additional six cycles of RB.OutcomesThe patients exhibited a slight reduction of the abnormal lymphocyte level but insufficient therapeutic efficacy during CHOP therapy. After the first cycle of RB, the patient exhibited an immediate response with the absence of minimal residual disease. He remained relapse-free for approximately 67 months. After a second relapse, complete response was again achieved with the absence of minimal residual disease following RB re-administration. He remained relapse-free for approximately 29 months after the second RB.ConclusionRB could be a treatment option for patients with relapsed or refractory HCL-v. Further research is needed to establish the optimal treatment regimen for patients of HCL-v.Copyright © 2021 the Author(s). Published by Wolters Kluwer Health, Inc.

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