High levels of Bcl3 are known to reduce RFS in patients with ER-positive breast cancer [38]; therefore, to elucidate the role of Bcl3 in regulating breast cancer cell survival, we began by assessing the effect of Bcl3 suppression in a range of ER-positive breast cancer cell lines expressing either wildtype or mutant forms of p53. This evidence concerns the gene BCL3 and breast cancer.