Although hairy cells are technically long-lived, instead of rapidly dividing, some late-stage patients are treated with broad-spectrum chemotherapy agents such as methotrexate that are effective at killing rapidly dividing cells. This is not typically attempted unless all other options have been exhausted and it is typically unsuccessful. Prognosis
Treatment success
More than 95% of new patients are treated well or at least adequately by cladribine or pentostatin. A majority of new patients can expect a disease-free remission time span of about ten years, or sometimes much longer after taking one of these drugs just once. If retreatment is necessary in the future, the drugs are normally effective again, although the average length of remission is somewhat shorter in subsequent treatments. There is also the risk of Shingles, and Peripheral Neuropathy after treatment with cladribine. As with B-cell chronic lymphocytic leukemia, mutations in the IGHV on hairy cells are associated with better responses to initial treatments and with prolonged survival.How soon after treatment a patient feels "normal" again depends on several factors, including:

how advanced the disease was at the time of treatment;
the patients underlying health status;
whether the patient had a "complete response" or only a partial response to the treatment;
whether the patient experienced any of the rare, but serious side effects such as kidney failure;
how aggressive the individuals disease is;
whether the patient is experiencing unusual psychological trauma from the "cancer" diagnosis; and
how the patient perceived his or her pre-treatment energy level and daily functioning. Lifespan
With appropriate treatment, the overall projected lifespan for patients is normal or near-normal.
Leukemic cells may gather in the spleen and cause it to swell; this can have the side effect of making the person feel full even when he or she has not eaten much.Hairy cell leukemia is commonly diagnosed after a routine blood count shows unexpectedly low numbers of one or more kinds of normal blood cells, or after unexplained bruises or recurrent infections in an otherwise apparently healthy patient.Platelet function may be somewhat impaired in HCL patients, although this does not appear to have any significant practical effect. It may result in somewhat more mild bruises than would otherwise be expected for a given platelet count or a mildly increased bleeding time for a minor cut, likely the result of producing slightly abnormal platelets in the overstressed bone marrow tissue. Patients with a high tumor burden may also have somewhat reduced levels of cholesterol, especially in patients with an enlarged spleen. Cholesterol levels return to more normal values with successful treatment of HCL. Cause
As with many cancers, the cause of HCL is unknown. Exposure to tobacco smoke, ionizing radiation, or industrial chemicals (with the possible exception of diesel) does not appear to increase the risk of developing it.