Either cladribine or pentostatin is likely to become the treatment of choice for patients with hairy cell leukaemia (HCL). Response rates and durations are far greater than those achieved with either interferon-α or splenectomy.
With regard to response rates, there is little to choose between these 2 drugs in HCL at present. However, recovery from neutropenia, anaemia and thrombocytopenia is more rapid with cladribine than with pentostatin. In addition, nausea, vomiting and disturbance of liver function tests do not seem to occur with cladribine at recommended dosages.
Only 1 course of cladribine is required to achieve response rates similar to those after several pentostatin infusions. However, the current cladribine regimen requires a 7-day hospital stay, while pentostatin can be given on an outpatient basis. If a 5-day intermittent cladribine regimen proves as effective as the 7-day continuous course, it may become feasible to administer cladribine to outpatients.
If one of these agents achieves responses that are significantly more durable than those produced by the other, it will become the drug of choice. In the meantime, the slightly better tolerability of cladribine may be an important factor in choosing between these 2 drugs.