Cladribine and Rituximab in Treating Patients With Hairy Cell Leukemia

Inclusion Criteria: * Age 18 years and older * Diagnosis of hairy cell leukemia (HCL) established by bone marrow examination * Patients with relapsed disease are eligible if they have had no more than one prior therapy * Women of child-bearing potential must use birth control (oral contraceptive, barrier, abstinence or any other acceptable method) for the duration of the study * Performance status =\< 3 * Creatinine less than or equal to 2.0 unless related to the disease * Bilirubin less than or equal to 3.0 * Transaminases less than or equal 3 x upper limit of normal unless related to the disease * No prior investigational agent in the 4 weeks prior to initiation of therapy Exclusion Criteria: * Unable or unwilling to sign the consent form * Known infection with human immunodeficiency virus (HIV), hepatitis B or C * Presence of active infection * Presence of central nervous system (CNS) metastases * New York Heart Association classification III or IV heart disease * Prior chemotherapy (last 4 weeks)