SIRT3 and cancer: Although some investigators have suggested a proapoptotic role for SIRT3,28-30 others have suggested a prosurvival role.20-22, 31 In addition, some reports suggest that SIRT3 is exclusively a mitochondrial protein12-18; however, others have reported that SIRT3 can be observed in the cytosol and nucleus during different cellular events.20, 32, 33 Those reports underscore the complexity of the biologic functions of sirtuins, which may differ according to their tissue of origin or cancer type.