Breast cancer susceptibility genes: Inherited factors that predispose to breast cancer. Put otherwise, these genes make one more susceptible to the disease and so increase the risk of developing breast cancer. Two of these genes, BRCA1 and BRCA2, have been identified (and prominently publicized). Several other genes (those for the Li-Fraumeni syndrome, Cowden disease, Muir-Torre syndrome, and ataxia-telangiectasia) are also known to predispose to breast cancer. However, since all of these known breast cancer susceptibility genes together do not account for more than a minor fraction (1/5th at most) of breast cancer that clusters in families, it is clear that more breast cancer genes remain to be discovered.