Hairy Cell Leukemia (HCL)

Hairy cell leukemia often present with a pancytopenia and an absence of monocytes (!! automated cell analyzers often mistake hairy cells for monocytes, giving a “monocytosis” !!). The cells are larger then normal lymphocytes, have an oval or indented (bean-shaped) nucleus with less clumped, homogeneous chromatin. Cytoplasm is abundant and pale with characteristic hairy extensions.
Diagnosis must always be confirmed by flow cytometry, cells are located is the SSC/CD45 plot within the mono-gate, are positive for CD19, CD20(strong), CD103, CD11c and negative for CD5, CD23 and CD10. CD25 is expressed on the classic HCL, but is absent in the variant type.