Chronic lymphocytic leukemia (CLL) is the most common adult leukemia in Western countries and is characterized by the clonal expansion of CD5+CD23+ B cells in the blood, bone marrow (BM), and secondary lymphoid tissues.1 Multiple myeloma (MM) is the second most common hematological malignancy and is characterized by the presence of abnormal clonal plasma cells in the BM.2 CLL and MM are hematological disorders that occur at different stages of B-cell development. This evidence concerns the gene CD5 and B-cell chronic lymphocytic leukemia.