Therapy Optimisation for the Treatment of Hairy Cell Leukemia

Inclusion Criteria: * Patients with histologically verified hairy cell leukemia * Presence of hairy cells in the bone marrow and peripheral blood detected by positive TRAP staining and / or co expression if cell surface antigens cluster of differentiation (CD) 19/CD25 or CD19/CD103 (b-ly7) * No previous cytostatic treatment (splenectomy or interferon treatment are allowed) * Need for treatment * Age at least 18 years old * General state of health according to WHO 0-2 * Current histology, not older than 6 months * Written consent by patient Exclusion Criteria: * Patients not fulfilling inclusion criteria above * Hairy cell leukemia variants (HCL-V): presence of lymphoid cells in bone marrow and / or peripheral blood, which have an intermediate morphology between hairy cells and prolymphocytes (negative TRAP staining and co- expression of CD19/CD103 without CD25 * Pretreatment with purine analogues or other chemotherapeutics * Concomitant corticosteroid therapy * Severe dysfunction of the heart (NYHA III or IV), the lung (WHO-Grade III or IV), the liver, except due to lymphoma (bilirubin \> 2 mg/dl, alkaline phosphatase, glutamate-oxalacetate transaminase and glutamate-pyruvate transaminase \> 2 x upper limit of normal), the kidneys (creatinin \> 2 mg/dl or creatinine clearance \< 50 ml/min), central nervous system diseases including psychoses. * Proven HIV infection * Active Hepatitis * Other florid infections * Anamnesis / diagnosis of other malignant disease (other than non-melanoma associated skin tumours or stage 0 in situ carcinoma of the cervix) * Pregnant or lactating women