In CLL cells, elevated levels of the cyclin-negative regulator p27-Kip1 protein are found in a majority of patients.33 Given the key role of this protein in cell cycle progression, its overexpression in CLL cells may account for the accumulation of B cells in early phases of the cell cycle.17 In addition, overexpression of the anti-apoptotic BCL-2, BCL-XL, BAG-1 and MCL-1 molecules and the absence of microRNAs miR-15 and miR-16,34 whereas proapoptotic proteins like BAX and BCL-XS are under expressed35 could explain the resistance of tumoral cells to apoptosis. Here, MCL1 is linked to B-cell chronic lymphocytic leukemia.