[1175] CD5-Positive Hairy Cell Leukemia: A Rare but Distinct Variant

D Chen, WG Morice, DS Viswanatha, CA Hanson. Mayo Clinic, Rochester, MN

Background: CD5-positive hairy cell leukemia (CD5+HCL) is a rare B-cell lymphoproliferative disorder. Its existence has been controversial due to overlapping phenotypic features with other mature B-cell neoplasms. Its clinicopathologic features have not been reported. In this retrospective study, we confirmed the existence of this rare HCL variant, and characterized its clinicopathologic features.
Design: We searched our bone marrow (BM) database for HCL cases that had CD5 coexpression by neoplastic B-cells. Out of a total of 157 HCL cases, we identified 5 CD5+HCL patients. Clinical data from each case were reviewed. Blood and BM specimens were examined including Tartrate-resistant acid phosphatase (TRAP) cytochemical studies, flow cytometric studies using a panel of B and T cell antibodies, and immunohistochemical (IHC) stains on BM biopsy sections using antibodies against CD20, TRAP, DBA-44, and cyclin D1. FISH analyses for CCND1/IGH translation were performed using BM aspirate samples.
Results: All 5 patients (median age: 59, range: 30-77; M:F = 4:1) had anemia, monocytopenia, circulating neoplastic lymphocytes, splenomegaly, and absent lymphadenopathy at presentation. All of the patients are alive (median follow-up in months: 32, range: 6-116). The neoplastic lymphocytes in all cases had reticulated chromatin, abundant cytoplasm, cytoplasmic projections, and numerous TRAP-positive cytoplasmic granules. The BM were extensively involved (range: 60-95%) and showed a typical interstitial infiltrative pattern. Monotypic B-cells in all cases expressed CD5 (dim to bright), CD20, CD22/CD11c, and CD103. IHC stains for TRAP and DBA-44 were all positive. Four patients, whose neoplastic B-cells coexpressed dim CD5, received 2-chlorodeoxyadenosine (2-CDA) treatment. All these 4 patients achieved excellent initial responses, 3 of which were confirmed by follow-up BM biopsies. Nevertheless, all of these 3 patients eventually had recurrent disease. In 1 case, neoplastic cells coexpressed bright CD5 and cyclin D1, and were also positive for CCND1/IGH translocation. This patient was initially treated as mantle cell lymphoma without response. Because its pathologic features and relatively indolent course were most consistent with HCL, this patient recently received 2-CDA treatment.
Conclusions: Rare CD5+HCLs do exist and have the common clinicopathologic features of HCL. They respond to initial 2-CDA treatment but may have a higher recurrence rate. It remains to be seen if the patient with the CCND1/IGH translocation will have a response to 2-CDA treatment as did the other CD5+HCLs.
Category: Hematopathology

Tuesday, March 10, 2009 9:30 AM

Poster Session III # 127, Tuesday Morning