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. This evidence concerns the gene CD5 and mantle cell lymphoma.