A 3-decade multicenter European experience with cladribine as upfront treatment in 384 hairy cell leukemia patients

: Cladribine is regarded as the first treatment of choice of symptomatic hairy cell leukemia (HCL): it provides high rates of response and very long duration of remission in some cases. Disease-specific patients records have been reviewed at four European centers of excellence; all patients with HCL requiring treatment who received frontline cladribine have been extrapolated. Responses have been classified according to Consensus Resolution Criteria. Three hundred and eighty-four patients have been diagnosed and followed between 1969 and 2018; all received frontline cladribine (subcutaneously or intravenously). A complete response was obtained in 72% of cases and a partial response in 22%. A continuous complete response was documented in 20% of patients at a median follow-up period of 8.5 years (range, 1-22 years). Median overall survival was reached at 25 years. Median progression-free survival was 13 years and median disease-free survival was 11 years. Cladribine is effective as frontline treatment of HCL and may determine deep disease control in a significant proportion of cases, given that more than 50% of treated patients require no further therapy. Good quality responses may be maintained for more than 20 years in up to 35% of patients.