Previous studies have showed that downregulated NPAS2 expression led to the cell cycle arrest at S and G2/M phase in colorectal cancer cells.12 NPAS2 silencing results in aberrant cell cycle response to DNA damage in breast cancer cells.21 In this study, we demonstrated that NPAS2 significantly facilitated cell survival both in vitro and in vivo by promoting cell cycle G1-S transition. This evidence concerns the gene NPAS2 and breast cancer.