Long-term follow-up of patients with hairy cell leukaemia after treatment with pentostatin or cladribine

We report the long-term follow-up results on two groups of patients with hairy cell leukaemia (HCL) treated with either pentostatin (deoxycoformycin) or cladribine (2-chlorodeoxyadenosine). 165 HCL patients received treatment with pentostatin (between 1986 and 1994), and 45 were treated with cladribine (between 1992 and 1997). Age and sex characteristics were similar in the two groups. 38 patients in the pentostatin group and 12 in the cladribine group were previously untreated. 22 patients in the cladribine group had received prior treatment with pentostatin; four were resistant, 17 had relapsed following partial (four) or complete (13) responses, and one was not evaluable for response. The response rates were the same in the two groups: 82% complete response (CR), 15% partial response (PR) for pentostatin and 84% CR, 16% PR for cladribine. Relapse rates were 24% for pentostatin and 29% for cladribine after median follow-up of 71 and 45 months respectively. At 45 months, however, the relapse rate for pentostatin was only 9.7%. We found a statistically significant difference in the disease-free interval (DFI) between the two groups suggesting that patients may relapse more quickly after cladribine. The majority of relapsed patients achieved second remissions following further therapy with either pentostatin or cladribine, with no evidence of cross resistance between the two agents. The 5-year survival for all patients was 97% and treatment- related toxicity was low. We conclude that both pentostatin and cladribine induce durable remissions in the majority of HCL patients. Longer follow-up is required to establish whether some patients are cured as there is no plateau in DFI, and which of these two agents may be the treatment of choice.