These findings not only confirm what has been shown in cancer [16,31,32] and systemic vascular smooth muscle cells [33,34] in which KLF5 inhibition decreases proliferation through cell cycle protein inhibition like cyclin B1 and p21 upregulation, but also provide a better demonstration of the involvement of KLF5 in mitochondrial-dependent apoptosis. This evidence concerns the gene CCNB1 and cancer.