MCL1 and B-cell chronic lymphocytic leukemia: The mechanisms behind the resistance of B-CLL to apoptosis are largely still undefined, but previous studies support a regulatory role of Bcl-2 family of apoptosis-regulatory proteins, such as Bcl-2/Bax and Mcl-1, in the survival of B-CLL cells (Aguilar-Santelises et al, 1996; Osorio et al, 1997; Kitada et al, 1998; Morales et al, 2005).