NPAS2 and breast cancer: In the context of hormone-sensitive cancers, NPAS2 gene down-regulation was found associated with poorly differentiated tumors in comparison with well- and moderately differentiated breast cancer [108] In addition, rs2305160 polymorphism of the NPAS2 gene (Ala394Thr) was found strongly associated with breast cancer risk and proposed as a candidate for breast cancer susceptibility [109,110,111].