CD5 and B-cell chronic lymphocytic leukemia: CLL is characterized by an outgrowth of malignant CD5 positive B cells, mainly residing in the peripheral blood (PB), bone marrow, and lymphoid organs, and by a high biological heterogeneity reflected in clinically different outcomes including disease progression, therapy response, and relapse (Kröber et al., 2002; Zenz et al., 2010).