Tubal ligation is protective because carcinogens are unable to reach the ovary and fimbriae via the vagina, uterus, and Fallopian tubes. Tubal ligation is also protective in women with the BRCA1 mutation, but not the BRCA2 mutation. Hysterectomy reduces the risk, and removal of both Fallopian tubes and ovaries (bilateral salpingo-oophorectomy) dramatically reduces the risk of not only ovarian cancer but breast cancer as well. This is still a topic of research, as the link between hysterectomy and lower ovarian cancer risk is controversial. The reasons that hysterectomy may be protective have not been elucidated as of 2015.