Early clearance of hairy cell leukaemia in the bone marrow after first‐line treatment with cladribine predicts a favourable outcome

First-line purine nucleoside analogues (PNAs) in hairy cell leukaemia (HCL) allow deep and long-lasting responses. We retrospectively analysed 53 HCL patients treated frontline with cladribine and assessed for response at 2 and 6months after treatment to evaluate the kinetics of response. The estimated median progression-free survival was significantly different according to the degree of residual HCL infiltrate detected by immunohistochemistry at the bone marrow biopsy at 2months (≤5% vs. >5%, 247 vs. 132months, respectively, p=0.033), but not at 6months (p=0.79). Our data suggest a favourable prognostic impact of early marrow HCL clearance in patients treated with cladribine.