The cumulative lifetime risk of developing breast cancer associated with a BRCA1 or BRCA2 mutation, up to age 80, may be as high as 72% and 69%, respectively (Kuchenbaecker et al. 2017), and approximately 5–10% of newly diagnosed breast cancers are thought to be attributable to a BRCA1 or BRCA2 mutation (Claus et al. 1996). Here, BRCA1 is linked to breast cancer.