Assessment of Disease Burden in Hairy Cell Leukemia

Inclusion Criteria: 1. Histologically confirmed diagnosis of HCL patients: 1. newly diagnosed and candidates for first-line cytoreductive treatment with analogues purines or 2. in relapse after a previous line of treatment, with indication for rescue therapy (repetition of a purine analogue; use of targeted or innovative drugs), except splenectomy or 3. in CR for at least 5 years after a first line of treatment, in the absence of clinical alterations indicative of a state of hematological relapse, or in any case in the absence of an indication for a new line of cytoreductive therapy (time-to-next treatment exceeding 5 years). 2. Age ≥ 18 years at enrollment 3. Signature of written informed consent Exclusion Criteria: 1\. Concomitant second malignancy.