ESR1 and breast neoplasm: 17, 18 In addition, it was demonstrated that ERα physically interacts and functionally cooperates with SIRT1 toward the stimulation of breast tumor cells.18 In accordance with these findings, the inhibition of SIRT1 led to the inhibition of ER-mediated signaling, thus indicating that SIRT1 may act as a co-activator of ERα.