HYBRID FORM OF HAIRY CELL LEUKEMIA AND CHRONIC LYMPHOCYTIC LEUKEMIA

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Abstract
We report a case with mixed features of hairy cell leukemia (HCL) and chronic lymphocytic leukemia (CLL), which may represent a hybrid form of these two entities. Hairy projections were demonstrated on leukemic cells in the peripheral blood. Surface marker studies of blood and spleen specimens by flow cytometry and immunohistochemistry showed immunophenotype characteristic of HCL, namely, monoclonal IgG‐kappa, positive reactions to CD 11c, CD 19, CD 20, CD 22, and HLA‐DR, but negative reactions to CD 3, CD 5, CD 7 and CD 10. The only atypical finding was the absence of CD 25. Immunogenotyping showed rearrangement of heavy‐chain and kappa light chain genes. Leukemic cells were also positive for tartrate‐resistant acid phosphatase (TRAP). A pseudosinus pattern was demonstrated in the spleen. However, the leukemic cells in the spleen showed atypical cytologic features. Clinically, the patient had generalized lymphadenopathy, high leukocyte counts, Coombs' negative hemolysis, hypoimmunoglobulinemia and IgG‐kappa monoclonal gammopathy, features more consistent with CLL than HCL. Although only CD 11c, CD 22, CD 25 and TRAP are characteristic for HLC and CD 5, characteristic for CLL, a panel of eight markers is recommended for the differential diagnosis of HCL, CLL and other low‐grade B‐cell neoplasms, which may share some common features, making a clear‐cut diagnosis difficult.