SIRT1 and breast cancer: SIRT1 expression and function has been studied in human breast cancer [27,28,29,30] and several other tumors in humans [31,32,33,34,35,36,37,38,39,40,41,42], in murine models [43,44], and in cultured tumor cells [45]; however, it has hitherto neither been investigated in canine mammary tumors nor in normal mammary gland tissues.