ABSTRACT
Hairy cell leukemia (HCL) is an indolent chronic B-cell lymphoproliferative disorder of mature lymphocytes with abundant cytoplasm, with “hairy” projections, characterized by diffuse bone marrow (BM) involvement, splenic red pulp involvement, monocytopenia, and pancytopenia (or less often anemia and neutropenia) [1–17]. BRAF V600E mutation, detected in ∼90% of cases, is described as a driver mutation [8,9,14,16,18–20]. A variant lacking CD25, annexin A1, TRAP, and the BRAF V600E mutation—called HCL variant (HCL-v)—is more aggressive and is classified as a separate disease [1]. HCL affects predominantly middle-aged and elderly men (the male to female ratio is between 4:1 and 5:1; median age at diagnosis is 55 to 60 years) and comprises ∼2–3% of all adult leukemias in the United States [7,21]. Patients present with symptoms of anemia, infections, and/or abdominal discomfort related to splenomegaly. Splenomegaly, hepatomegaly, and intraabdominal adenopathy are present in 60–70%, 40–50%, and 15–20% of patients, respectively [22]. Leukemic cells have a characteristic cytomorphology (hairylike cytoplasmic protrusions) and immunophenotype (CD25+/CD103+). Factors associated with a worse prognosis include high WBC count, low hemoglobin levels, and prominent splenomegaly. Treatment of HCL is usually considered for symptomatic patients (significant neutropenia, anemia, thrombocytopenia, symptomatic splenomegaly, constitutional symptoms, or recurrent serious infections) [5,23–25]. Interferon treatment induces remission in approximately 90% of patients, but complete remission is obtained in only 5% to 10% [24]. Currently, the standard treatment of HCL includes purine analogues 2-deoxyadenosine (2-CDA; cladribine) and 2-deoxycofrormycin (pentostatin; DCF, or Nipent), which are associated with better response rates than with interferon-a and with long-lasting remissions [25,26]. Pentostatin and cladribine are considered interchangeable in terms of efficacy [10]. Other new treatment options include rituximab and BL22 immunotoxin [6]. Infectious complications, which were common in the past and the major cause of death, have become rare in the era of purine analog therapy [2].
