Image Description
In HCL, the addition of tartrate does not inactivate the enzyme acid phosphatase within the neoplastic cells - i.e. they are tartrate-resistant, a feature not seen in most other leukemias and lymphomas. With tartrate-resistant acid phosphatase (TRAP) stain, the hairy cells show red granular cytoplasmic staining. The TRAP activity is labile and the stain must be performed on air-dried smears soon after the slides are prepared. Nowadays, the TRAP cytochemistry has been largely replaced by TRAP immunohistochemistry (shown here). It must be remembered that TRAP immunostains are not as specific as TRAP cytochemistry and may stain other B-cell neoplasms. Image courtesy of: Jared Block, MD, Carolinas Pathology, Charlotte, NC; Sciplicity, LLC.
About the Disease
Hairy Cell Leukemia (HCL) is a mature B-cell neoplasm that mainly involves the blood, bone marrow, and splenic red pulp. It makes up only about 2% of all leukemias and predominantly affects middle-aged men (M:F = 4:1).The clinical features are often related to cytopenias and include recurrent infections (due to neutropenia) and weakness and fatigue (due to anemia). Monocytopenia is one of most sensitive markers of HCL. Splenomegaly is seen in 80% to 90% of cases; lymphadenopathy is uncommon. A small proportion of patients show polyclonal hypergammaglobulinemia. In about one-fourth of the patients, HCL is diagnosed incidentally.The neoplastic lymphocytes have an ill-defined, ruffled cytoplasmic border with hair-like surface projections. They express B-cell associated antigens CD19, CD20, and CD22. In addition, they are positive for CD103, CD25, and CD11c.