Hairy Cell Leukemia

This chapter includes answers to practice-based questions with case studies covering the new principles of diagnosis and treatment in Hairy Cell Leukemia (HCL). HCL variant and splenic marginal zone lymphoma are biologically different diseases that can mimic classical HCL and have a worse prognosis, are treated differently, and should be excluded at diagnosis. Single-agent therapy with a purine analog, either cladribine or pentostatin, has been the standard front-line therapy for patients with symptomatic HCL for the past 25 years. Cladribine and pentostatin are purine analogs that interfere with normal purine metabolism. Both agents are highly effective in HCL, but cladribine is usually preferred given its safety profile and tolerability as well as the convenience of administration compared to pentostatin. Cladribine is administered intravenously when treating symptomatic HCL, although there are oral and subcutaneous formulations available. Moxetumomab pasudotox was approved for relapsed/refractory HCL based on durable complete remissions.