Which statement describes the typical presentation and immunophenotype of chronic lymphocytic leukemia (CLL) compared with small lymphocytic lymphoma (SLL)?

• A. CLL presents with circulating lymphocytosis with bone marrow involvement; SLL presents with lymphadenopathy; immunophenotype is CD5+, CD23+, CD19+, CD20+.
• B. SLL presents with circulating lymphocytosis; CLL presents with lymphadenopathy; immunophenotype is CD3+, CD7+.
• C. CLL and SLL are identical diseases; immunophenotype is CD10+ only.
• D. CLL lacks CD5 expression; SLL expresses CD5 and CD23.

Answer: (A)

CLL and SLL are essentially the same disease seen in different places: CLL shows clonal B cells in the blood with circulating lymphocytosis and often bone marrow involvement, while SLL presents mainly with lymph node enlargement and little to no circulating lymphocytosis. The immunophenotype that ties them together is a B-cell profile that unusually coexpresses CD5 and CD23 along with CD19 and CD20. This CD5+/CD23+ pattern on B cells is a hallmark that helps distinguish CLL/SLL from other B-cell neoplasms. The statement fits this picture: CLL with circulating lymphocytosis and marrow involvement, SLL with lymphadenopathy, and the characteristic CD5+, CD23+, CD19+, CD20+ immunophenotype.