BCL2 and neoplasm: The intrinsic pathway involves mitochondrial events that induce the opening of the mitochondrial permeability transition pore (mPTP) through positive or negative signalling, releasing proapoptotic proteins and cytochrome C. BCL2 proteins are the key regulators of the intrinsic pathway and include multiple members [18], such as BCL2 and BCL-XL, which are highly expressed in tumour cells and defend against apoptosis by regulating mitochondrial membrane potential and cytochrome C release, thus altering cell fate [19].