Regulation of cell death. Apoptosis involves a sensor that detectspro-apoptotic stimuli, a signal transduction network, and execution machinery.Despite the complexity of its regulation, execution of programmed cell death iseffected by the well-defined family of caspases. Upstream, at least one familyof proteins exist at each level of response to pro-apoptotic stimuli that isable to block a deadly signal, including the heat shock proteins (HSPs), theanti-apoptotic death effector domain proteins (ADEDs), several members of theBcl-2 family, the inhibitors of apoptosis proteins (IAPs), and the nuclearfactor-κB (NF-κB) family of transcription factors. Conversely,executioners of apoptosis such as Bax may be not functional, inclining thebalance towards inappropriate survival of the tumor cell. In breast cancer,many of these proteins are dysregulated. BID, Bcl-2 homology domain 3interacting domain death agonist; TNF, tumor necrosis factor; TRAIL,TNF-related apoptosis-inducing ligand.