Six loci (at TOX3, 2q35, 6q25.1, 19p13, CASP8 and wild-type copy of BRCA1) are now known to be associated with breast cancer risk for BRCA1 mutation carriers; a further 10 loci (at FGFR2, TOX3, MAP3K1, LSP1, 2q35, SLC4A7, 5p12, 1p11.2, ZNF365 and RAD51) have been associated with breast cancer risk for BRCA2 carriers. This evidence concerns the gene MAP3K1 and breast cancer.