CD5 and B-cell chronic lymphocytic leukemia: Chronic lymphocytic leukemia (CLL) and mantle cell lymphoma (MCL) are 2 lymphoid neoplasms characterized by the proliferation and accumulation of mature small CD5+ B cells, commonly involving bone marrow, blood, and lymphoid organs.1 CLL is considered an indolent disease, whereas the clinical course of the majority of MCL patients is more aggressive.