An attempt may be made then to end the treatment, but most patients discover that they need to continue taking the drug for it to be successful. These patients often continue taking this drug indefinitely, until either the disease becomes resistant to this hormone, or the body produces an immune system response that limits the drugs ability to function. A few patients are able to achieve a sustained clinical remission after taking this drug for six months to one year. This may be more likely when IFN-alpha has been initiated shortly after another therapy. IFN-alpha is considered the drug of choice for pregnant women with active HCL, although it carries some risks, such as the potential for decreased blood flow to the placenta. IFN-alpha works by sensitizing the hairy cells to the killing effect of the immune-system hormone TNF-alpha, whose production it promotes. IFN-alpha works best on classic hairy cells that are not protectively adhered to vitronectin or fibronectin, which suggests that patients who encounter less fibrous tissue in their bone-marrow biopsies may be more likely to respond to IFN-alpha therapy. It also explains why unadhered hairy cells, such as those in the bloodstream, disappear during IFN-alpha treatment well before reductions are seen in adhered hairy cells, such as those in the bone marrow and spleen. Other treatments
Splenectomy can produce long-term remissions in patients whose spleens seem to be heavily involved, but its success rate is noticeably lower than cladribine or pentostatin.
Most patients receive cladribine by IV infusion once a day for five to seven days, but more patients are being given the option of taking this drug once a week for six weeks. The different dosing schedules used with cladribine are roughly equally effective and safe. Relatively few patients have significant side effects other than fatigue and a high fever caused by the cancer cells dying, although complications such as infection and acute kidney failure have been seen. Pentostatin is chemically similar to cladribine, and has a similar success rate and side effect profile, but it is always given over a much longer period of time, usually one dose by IV infusion every two weeks for 3–6 months. During the weeks following treatment, the patients immune systems are severely weakened, but their bone marrow will begin to produce normal blood cells again. Treatment often results in long-term remission. About 85% of patients achieve a complete response from treatment with either cladribine or pentostatin, and another 10% receive some benefit from these drugs, although no permanent cure for this disease is known. If the cancer cells return, the treatment may be repeated and should again result in remission, although the odds of success decline with repeated treatment. Remission lengths vary significantly, from one year to more than twenty years. The median patient can expect a treatment-free interval of about ten years. 2-Chlorodeoxyadenosine (Cladribine) induced complete responses in patients with hairy cell leukemia resistant to DCF, suggesting a lack of cross-resistance.