CDKN1A and breast cancer: A number of SNPs of several genes have been associated with susceptibility to early onset of BC, such as HER2 Ile655Val (Montgomery et al., 2003), MDM2 SNP309 and p53 Arg72Pro (Sun et al., 2009), ER1 594G to A (Yu et al., 2006) and p21 Ser31Arg (Ma et al., 2006; Qiu et al., 2010).