SIRT1 and neoplasm: However, on the contrary, some studies are in support of a tumor promoter role of SIRT1: an increased expression of SIRT1 correlated with p53 inactivation, together with apoptosis reduction, was found in human breast cancer cells [63], and, in breast cancer also, SIRT1 upregulation was found by another group, yet this study did not consider any subcellular SIRT1 expression [64].