Image Description
On flow cytometry, hairy cells show high forward light scatter and slightly higher side light scatter than the normal lymphocytes. They usually fall outside of the lymphocyte region within the monocyte gate (see bottom right panel). HCL expresses bright CD45 and B-cell markers such as CD19, CD20 (bright), CD22, FMC-7, and CD79a. In addition, the neoplastic cells show bright expression of CD11c, CD25, CD103, and CD123. They are usually negative for CD5, CD10, and CD79b. About 10% to 25% of cases with classic features of HCL may show CD10 expression (as seen in this case). It is useful to remember that the vast majority of HCL cases express at least 3 of the following 4 markers : CD11c, CD103, CD25, and CD123. 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.