Image Description
HCL expresses B-cell markers such as CD19, CD20, CD22, FMC-7, and CD79a. Although immunohistochemistry on bone marrow biopsy sections is not essential for diagnosis in routine cases, it might be helpful in highlighting the tumor cell population when the marrow involvement is subtle. B-cell markers such as CD20 (shown here) are helpful in distinguishing HCL (which will show strong positivity) from conditions that enter into the differential diagnosis such as myelodysplastic syndrome or aplastic anemia. Immunostaining with antibodies to DBA.44 or CD20 is also useful in assessing minimal residual disease following therapy. 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.