Analysis of CD 10 + Hairy Cell Leukemia

Hairy cell leukemia (HCL) has been reported to sometimes express CD10. However, the reported frequencies have been quite variable and the significance of CD10 expression has not been addressed. Cases of HCL submitted to our flow cytometry service during a 2-year period were evaluated for CD10 expression. Information regarding demographics, clinical manifestations, tissue morphologic features, and response to treatment was reviewed. Of the 97 HCL cases identified, 10 expressed CD10. The level of CD10 staining was typically well above control levels and also could be detected easily by immunohistochemical analysis. All cases analyzed were negative for bcl-6. Our study suggests that approximately 10% of otherwise typical cases of HCL show aberrant CD10 expression. CD10+ HCL cases seem to be morphologically and clinically similar to CD10– HCL cases. Appreciating that HCL can express CD10 may be especially important when evaluating specimens with suboptimal morphologic features and/or limited immunophenotyping panels. Hairy cell leukemia (HCL) is a distinct type of mature B-cell lymphoproliferative disorder that affects primarily older adults (median age at onset, 55 years) and shows a male predominance (male/female ratio of approximately 5:1). 1 The major sites of disease involvement usually are the spleen and bone marrow, and most patients have pancytopenia and splenomegaly at initial examination.1,2 HCL has a characteristic immunophenotype with almost all cases being positive for surface CD103, bright CD22, CD11c, and CD25.3-5 This immunophenotype is not observed in other mature small B-cell neoplasms and, therefore, generally can be used to establish a definitive diagnosis.4,6,7 Although HCL is classically thought to be negative for CD10 expression, several studies have reported finding CD10+ HCL cases,3,5,8 with one reporting a frequency of approximately 25%. 3 CD10 is an important phenotypic marker used typically to identify mature B-cell neoplasms of follicular center cell origin, ie, follicular lymphoma, Burkitt lymphoma, and a subset of diffuse large B-cell lymphomas.9,10 Reports of relatively high numbers of CD10+ HCL cases raise the possibility that this neoplasm also may be of follicular center cell origin or represent a subset that differs pathologically and/or clinically from more typical CD10– HCL cases. We report on 11 cases of CD10+ HCL derived from the database of a large reference flow cytometry laboratory. Although other studies have identified CD10+ HCL cases, none have specifically addressed whether CD10+ HCL cases might differ morphologically, clinically, or in other ways from CD10– HCL cases or whether CD10 expression was stable or specimen type–dependent. In addition, we wanted to take advantage of the large number of cases seen in our Hematopathology / ORIGINAL ARTICLE Am J Clin Pathol 2003;120:228-235 229 229 DOI: 10.1309/QVJD31TEG9UJ18BQ 229 © American Society for Clinical Pathology reference flow cytometry laboratory, as the frequency of CD10+ HCL cases reported in other relative large studies has been quite variable, ranging from 5% to 26%. 3,5 Materials and Methods Case Selection and Patient Information The ARUP flow cytometry database (Salt Lake City, UT) was searched for records from January 1999 to October 2002 of cases of monoclonal B-cell lymphoproliferative disorders with a characteristic HCL phenotype (CD11c+, CD22+, CD25+, and CD103+). Specimens submitted for phenotyping included peripheral blood, bone marrow, spleen, and fine-needle aspirates of tissues. Flow Cytometric Immunophenotyping Specimen processing and antibody staining were performed as previously described.11 Antibodies against CD3 (SK7), CD5 (L17F12), CD7 (4H9), CD11c (S-HCL-3), CD20 (L27), CD22 (S-HCL-1), CD25 (2A3), κ (TB28-2), and λ (1-155-2) were obtained from BD Bioscience (San Jose, CA). Antibodies against CD2 (SCFC13PT2H9), CD4 (SFCI12T4D11), CD8 (SCFCI21thy3D3), CD10 (J5), CD19 (J4.119, HD237, 89B), and CD45 (J.33) were obtained from Beckman Coulter (Miami, FL). Antibodies against CD10 (SS2/36), CD103 (Ber-ACT8), and polyclonal κ and λ were obtained from DAKO (Carpinteria, CA), while an antibody against CD45 (HI30) was obtained from Caltag (Burlingame, CA). All antibodies were conjugated directly with fluorescein isothiocyanate, phycoerythrin (PE), PE– Texas red, or PE–cyanin 5.1. Data acquisition and analysis were performed with an EPICS XL cytometer and EXPO32 software (Beckman Coulter). Both 3and 4-color analyses were performed using CD45 and light scatter gating to identify cell populations and exclude debris. HCL cases were considered positive for CD10 expression if CD10 was present on at least 20% of the monoclonal B cells relative to isotype controls and formed a distinct population. Some of the flow cytometric results also were repeated on cryopreserved viable cells, which gave values similar to the initial studies that are reported.