to be very low. For example, one round of either cladribine or pentostatin gives the median first-time patient a decade-long remission; the addition of rituximab, which gives the median patient only three or four years, might provide no additional value for this easily treated patient. In a more difficult case, however, the benefit from the first drug may be substantially reduced, so a combination may provide some benefit. First-line therapy Cladribine (2CDA) and pentostatin (DCF) are the two most common first-line therapies. They both belong to a class of medications called purine analogs, which have mild side effects compared to traditional chemotherapy regimens. Cladribine can be administered by injection under the skin, by infusion over a few hours into a vein (inravenous - IV), or by a pump worn by the patient that provides a slow drip into a vein, 24 hours a day for 7 days. 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. Also, 2-CdA is not