Jolie's mother died of breast cancer at 56. Jolie was careful to explain why her situation was unusual. "Only a fraction of breast cancers result from an inherited gene mutation," she wrote. About 5 to 10 percent of all breast cancers are related to a BRCA 1 or BRCA 2 mutation. But a new study shows that while her story certainly got a lot of attention, it unfortunately didn't do much to increase people's understanding of actual breast cancer risk.