Neoplastic lymphoid cells of chronic lymphocytic leukemia (CLL) typically co-express CD5 and CD23. CD5-negative CLL is a rare variant of CLL; only 1 case of it has been reported in Korea. We describe a case of CD5-negative CLL. A 48-year-old female complained of a palpable neck mass that had been present for over 1 year. The initial WBC count was 7,300/ՌL, with 69% lymphocytes. A CT scan revealed multiple enlarged lymph nodes, both of each in the neck, axilla, and common iliac areas. The athologic results of the cervical lymph node was consistent with small lymphocytic lymphoma, of which tumor cells do not express CD5. In a bone marrow study, neoplastic lymphoid cells comprise 34.8% of all nucleated cells, which showed small size, round nuclei with clumped chromatin, and sparse cytoplasm. Immunophenotyping of small lymphoid cells displayed phenotypes that were CD45-, CD23-, CD20-, and CD19-positive, but CD5-negative. The patient was diagnosed with CD5-negative CLL, and has been followed up for 2.5 years after chemotherapy. (Korean J Hematol 2009;44:255-260.)

Keywords: Chronic lymphocytic leukemia, CD5 antigen, Immunophenotyping