Among highly potent and specific small-molecule inhibitors targeting these anti-apoptotic Bcl-2 proteins, ABT-263 [13], [21] and ABT-199 [18] have been advanced into clinical development and both compounds have demonstrated impressive antitumor activity as single agents in patients with chronic lymphocytic leukemia, in which the cells are primarily dependent upon Bcl-2 for survival. This evidence concerns the gene BCL2 and B-cell chronic lymphocytic leukemia.