CD5 and leukemia: CLL/SLL is a B-cell lymphoma characterized by the accumulation of clonal mature CD5-expressing B cells in the blood, bone marrow, lymphoid and extra-nodal tissues [4]. CLL/SLL accounts for approximately 25 to 30% of all leukemia in the U.S. Median age at diagnosis is 70 years [2,5]. Most cases of CLL/SLL are preceded by monoclonal B-cell lymphocytosis.