• Epidemiology
  • Most common in middle-aged men
  • ♂ > ♀ (4:1)
• Pathology: mature B-cell tumor; BRAF mutations are common
• Clinical features
  • Symptomatic pancytopenia
  • Massive splenomegaly
  • No lymphadenopathy
  • B symptoms are rare.
• Diagnostics
  • Usually tartrate-resistant acid phosphatase (TRAP) stain positive
  • Flow cytometry (preferred over TRAP stain): CD11c marker
  • CBC: Leucopenia is common but up to 20% of patients have leukocytosis.
  • Peripheral blood smear: Hairy cells have irregular cytoplasmic projections that cause the characteristic “hairy” appearance.
  • Bone marrow aspiration: often yields a dry tap due to bone marrow involvement with subsequent fibrosis