BRCA1 is a gene that increases the risk of getting breast, ovarian, bowel or prostate cancer. Out of every 100 women who have a faulty version of the BRCA1 gene, between 50 to 80 will develop breast cancer at some point in their life. So they have a lifetime risk of 50 to 80%. Ovarian cancer lifetime risk is about 40%. The lifetime risk of bowel cancer and prostate cancer is about 6%.