Long‐term durable remission by cladribine followed by rituximab in patients with hairy cell leukaemia: update of a phase II trial

Summary Nucleoside analogues are highly active in patients with hairy cell leukaemia (HCL); however, patients continue to relapse. This phase II study evaluated the efficacy and safety of cladribine followed by rituximab in patients with untreated HCL ( N = 59), relapsed HCL ( N = 14) and HCL variant (HCLv, N = 7). Cladribine 5·6 mg/m 2 was given intravenously (IV) daily for 5 d and was followed approximately 1 month later with rituximab 375 mg/m 2 IV weekly for 8 weeks. Complete response rate in patients with untreated HCL, relapsed HCL and HCLv was 100%, 100% and 86%, respectively. With a median follow up of 60 months, 5‐year failure‐free survival (FFS) in patients with untreated HCL, relapsed HCL and HCLv was 95%, 100% and 64%, respectively. Median duration of response to the cladribine followed by rituximab was significantly longer than the first‐line cladribine single agent in patients who received this treatment as second‐line treatment (72 months vs not reached, P = 0·004). Almost all patients (94%) achieved negative minimal residual disease (MRD) after the treatment. Positive MRD during the follow up did not necessarily result in clinically relevant relapse. Cladribine followed by rituximab is highly effective even in patients with relapsed disease and HCLv, and can achieve durable remission.