The BCL-2 protein family plays a large role in determining whether cancer cells survive in response to therapy or undergo a form of cell death known as apoptosis. Cells are pressured toward apoptosis by expression of pro-apoptotic BCL-2 proteins. However, cancer cells respond to therapy by increasing expression of anti-apoptotic proteins, which bind and neutralize pro-apoptotic family members and mediate therapeutic resistance. Therefore, development of therapeutic strategies to neutralize resistance to apoptosis will be critical to clinical improvements.