Leukemia & Lymphoma, June 2011; 52(S2): 11–13
Diagnosis of hairy cell leukemia by flow cytometry
MARYALICE STETLER-STEVENSON & PRASHANT R. TEMBHARE Flow Cytometry Unit, Laboratory of Pathology, National Cancer Institute, National Institutes of Health, Bethesda, MD, USA
Abstract Flow cytometric immunophenotpying (FCI) is a vital tool in the diagnosis of hairy cell leukemia (HCL). HCL has a distinctive immunophenotype based upon staining with antibodies to CD5 (negative), CD10 (negative), CD23 (negative), CD20 (abnormally bright), CD22 (abnormally bright), CD11c (abnormally bright), CD25 (abnormally bright), CD103 (positive), and CD123 (positive). Due to this unique immunophenotype, FCI can differentiate malignant hairy cells from normal B-cells and other lymphoproliferative disorders, especially the morphologically similar hairy cell leukemia variant and splenic lymphoma with villous lymphocytes. FCI is extremely sensitive in the detection of minimal disease and is useful in monitoring response to therapy.
Keywords: flow cytometry, hairy cell leukemia, CD103, CD11c, CD123
Flow cytometric immunophenotpying (FCI) pro- vides enhanced sensitivity and specificity in the diagnosis of hairy cell leukemia (HCL). Historically, diagnosis was based on evaluation of bone marrow and peripheral blood for hairy cells and demonstra- tion of tartrate resistant acid phosphatase (TRAP) staining to confirm the diagnosis. However, bone marrow aspiration is frequently unsuccessful in these patients and the biopsy specimen may be insufficient for a definitive diagnosis. Moreover, peripheral blood involvement often is minimal, making identification of hairy cells by light microscopic examination difficult. In addition, hairy cell leukemia is difficult to distinguish from splenic lymphoma with villous lymphocytes (SLVL) by morphologic examination alone, and TRAP staining can be negative in HCL and positive in other lymphoproliferative disorders [1,2]. Since HCL has a distinctive flow cytometric immunophenotypic profile that is different from normal B-cells and other lymphoproliferative dis- orders, FCI can provide a definitive diagnosis of this disease. Furthermore, due to the ability to rapidly evaluate large numbers of cells, FCI can detect
extremely low numbers of HCL cells and is more sensitive than standard polymerase chain reaction (PCR) B-cell clonality studies in detecting low-level HCL [3]. Although hairy cell leukemia variant (HCLv) has similar splenic and bone marrow pathological features to that of classical HCL, it has a markedly different clinical course, response to treatment, and immunophenotype. Because of the different outcomes of classical HCL and HCLv, a distinction between the two diseases becomes a relevant clinical issue, and FCI is useful in making the diagnosis [4]. Classical HCL has a diagnostic immunophenotype
that is readily identifiable by FCI. Hairy cells are monoclonal with surface light chain restriction. In contrast to the majority of B-cell lymphoproliferative disorders, lambda light chain restriction is highly prevalent, with either a predominance of lambda or equal incidence of kappa and lambda restriction [1,5]. The hairy cells characteristically express CD19, CD20, CD22, CD79b, FMC7, CD11c, CD25, CD103, and CD123 but are negative for CD5, CD10 (positive in 5–14% of cases) and CD23
Correspondence: Dr. Maryalice Stetler-Stevenson, NIH, NCI, 9000 Rockville Pike, Bethesda, MD 20892, USA. E-mail:
stetler@mail.nih.gov
ISSN 1042-8194 print/ISSN 1029-2403 online 2011 Informa UK, Ltd. DOI: 10.3109/10428194.2011.570820
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