Polymorphisms in CLOCK (Hoffman et al., 2010; Truong et al., 2014), NPAS2 (Zhu et al., 2008), CRY2 (Hoffman et al., 2010), RORA (Truong et al., 2014), TIMELESS (Fu et al., 2012), and ARNTL (Zienolddiny et al., 2013) have been associated with breast cancer. This evidence concerns the gene NPAS2 and breast cancer.