Preventative removal of the ovaries and the fallopian tubes may reduce the chances of ovarian cancer by 90%, and if done before menopause, can reduce the risk of breast cancer as well.
Mastectomy can reduce the risk of breast cancer by 90%.
Hormone blocking or chemo preventative medications such as tamoxifen, raloxifene, exemestane, and anastrozole may reduce the risk of breast cancer by as much as 50%.
Oral contraceptives (birth control pills) reduce the risk of ovarian cancer; however, they may increase the risk of breast cancer.