In brief: BRCA1 and BRCA2.

The discovery of the first major breast cancer susceptibility gene, BRCA1, occurred almost 20 years ago. BRCA1, together with BRCA2 remain the most important discoveries in human cancer genetics. Identification of highly penetrant mutations in these two tumour suppressor genes has had broad implications for women at risk and their families, for health professionals caring for these persons and for basic researchers. The BRCA proteins have many critical functions, the most notable of which, from a clinical perspective, is repair of double-strand DNA breaks.
(Copyright © 2013 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.)