Of the nine SNPs associated with breast cancer risk in BRCA1 mutation carriers, three were primarily associated with estrogen receptor (ER)-negative breast cancer: rs11806633 at 1q42.13 in the CDC42BPA gene (p = 9.0 × 10−3), rs6721310 at 2p23.2 in the BRE gene (p = 3.0 × 10−3), and rs2305354 at 2q11.2 in the REV1 gene (p = 1.0 × 10−3), although the differences between ER-positive and ER-negative disease associations were not statistically significant (Table 2). This evidence concerns the gene CDC42BPA and breast cancer.