That's according to a new British study of some 3,500 women at high risk of breast cancer.
Those women had at least a 25% lifetime risk of developing breast cancer. That means that at least a quarter of them would likely develop breast cancer sometime during their lives.
For comparison, the lifetime breast cancer risk for U.S. women is 12%, according to the National Cancer Institute. Breast cancer risk varies from woman to woman, based on many breast cancer risk factors.
In the new study, 211 women knew they had BRCA1 or BRCA2 gene mutations, putting them at very high risk of breast cancer and ovarian cancer. The other women didn't know if they had the BRCA1 or BRCA2 gene mutations.
Each woman was counseled about her breast cancer risk and about the option of prophylactic mastectomy, which is surgery to remove both breasts while they're still cancer-free. Women with the BRCA1 or BRCA2 gene mutations could also get surgery to remove their ovaries, in light of their ovarian cancer risk.
The women were free to choose surgery or not, and they could take as long as they wanted to make that decision.
Women with BRCA1 or BRCA2 gene mutations, women at very high risk of breast cancer, and women ages 35-45 were the most likely to choose preventive mastectomy.
Among women with BRCA1 or BRCA2 gene mutations, those age 35-45 were the most likely to choose surgery to remove their ovaries. Younger women may delay that until after they're done having children, note the researchers, who included D. Gareth Evans, MD, a professor at England's University of Manchester.
In some cases, the decision to get prophylactic mastectomy took many years.
"Women have their breasts or ovaries removed based on their risk. It does not always happen immediately after counseling or a genetic test result and can take more than seven years for patients to decide to go forward with the surgery," Evans says in a news release.
The study doesn't show why the women chose to get, delay, or skip preventive surgery. It's a balancing act between their cancer risk, cancer fears, life stage, and other commitments, write Evans and colleagues.
The U.K.'s national health care system covered genetic testing and the women's operations. It's not clear if the study's findings apply to women in other countries.