patients, may be a more important poor prognostic factor than variant status, with HCL-V patients without the VH4-34 rearrangement responding about as well as classic HCL patients. Hairy cell leukemia-Japanese variant The variant called hairy cell leukemia-Japanese variant, or HCL-J, is more easily treated. Treatment with cladribine has been reported. Prevention Because the cause is unknown, no effective preventive measures can be taken, but the U.S. Institute of Medicine permits an association to exposure to herbicides (atrazine). The U.S. Department of Veterans Affairs also considers it a service disability related to Agent Orange. Because the disease is rare, routine screening is not cost effective. Treatment Several treatments are available, and successful control of the disease is common. Not everyone needs treatment immediately. Treatment is usually given when the symptoms of the disease interfere with the patient's everyday life, or when white blood cell or platelet counts decline to dangerously low levels, such as an absolute neutrophil count below 1000 cells per microliter (1.0 K/μL). Not all patients need treatment immediately upon diagnosis. Treatment delays are less important than in solid tumors. Unlike most cancers, treatment success does not depend on treating the disease at an early stage. Because delays do not affect treatment success, no standards exist for how quickly a patient should receive treatment. Waiting too long, though, can cause its own problems, such as an infection that might have been avoided by proper treatment to restore immune-system function. Also, having a higher number of hairy cells at the time of treatment can make certain side effects somewhat worse, as some side effects are primarily caused by the body's natural response to the dying hairy cells. This can result in the hospitalization of a patient whose treatment would otherwise be carried out entirely at the hematologist's office. Single-drug treatment is typical. Unlike most cancers, only one drug is normally given to a patient at a time. While monotherapy is normal, combination therapy—typically using one first-line therapy and one second-line therapy—is being studied in current clinical trials, and is used more frequently for refractory cases. Combining rituximab with cladribine or pentostatin may or may not produce any practical benefit to the patient. Combination therapy is almost never used with a new patient. Because the success rates with purine analog monotherapy are already so high, the additional benefit from immediate treatment with a second drug in a treatment-naïve patient is assumed