Concurrent rituximab with first-line cladribine may improve outcomes among patients with hairy cell leukemia (HCL), according to research published in the Journal of Clinical Oncology.1

HCL is an indolent disease, and accounts for about 2% of all leukemia cases in the United States. Cladribine and pentostatin, standard first-line purine analogs, usually result in complete response (CR) rates of 75% to 90%. Yet as these treatments do not remove minimal residual disease (MRD), relapse occurs at a median of 4.5 to 16 years after treatment.

Rituximab has some single-agent activity in HCL, but there is evidence that it may eliminate MRD when used with cladribine or pentostatin. The optimal time to use rituximab in this disease setting is not, however, well established.

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For this randomized phase 2 trial, researchers assigned 68 patients with HCL 1:1 to receive cladribine with concurrent or delayed rituximab, in an effort to determine the efficacy of both combinations in the first-line setting. The median patient age was 48 years (range, 29-77), and there was no baseline difference in neutropenia or thrombocytopenia rates between the 2 arms.

Patients in both groups had an objective response rate of 100% at 6 months, though the CR rates and MRD-negativity rates were better in the concurrent rituximab group (100% and 97%, respectively) than in the delayed rituximab group (88% and 24%, respectively). Both groups, however, had better MRD-negativity and CR rates than those seen in previous studies of cladribine monotherapy in this setting.

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Grade 3 to 4 adverse events in the concurrent group included lymphopenia (74%), leukopenia (65%), thrombocytopenia (59%), and low CD4 count (56%); grade 3 to 4 events in the delayed group included leukopenia (74%), lymphopenia (65%), and low CD4 count (59%).

“Because of the effectiveness of delayed rituximab, it will take much longer to determine a difference in clinical relapse between randomly assigned groups, and the difference between the delayed group and historical patients receiving cladribine monotherapy may become obvious before that time,” the authors wrote.


Chihara D, Arons E, Stetler-Stevenson M, et al. Randomized phase II study of first-line cladribine with concurrent or delayed rituximab in patients with hairy cell leukemia [published online February 28, 2020]. J Clin Oncol. doi: 10.1200/JCO.19.02250