With the development of treatments such as poly(ADP-ribose) polymerase (PARP) inhibitors that are targeted to the specific defects in DNA repair pathways which exist in BRCA1 deficient cancers [21], it is important to determine whether ER+ breast cancers that develop in BRCA1 mutation carriers are incidental (that is, not directly related to the BRCA1 mutation/BRCA1 dysfunction) or if they are mutation-related in order to determine whether such BRCA1-targeted therapies might be effective in this population. This evidence concerns the gene BRCA1 and breast cancer.