In the study, researchers from the Dana-Farber Cancer Institute in Boston, led by Deborah Schrag, MD, MPH, used a mathematical decision-making model to estimate how a woman’s life expectancy might be affected by prevention options. Their findings provide important information for women with this type of breast cancer.

These women are at particularly high risk of developing cancer in the unaffected breast or developing ovarian cancer later on, so they often face difficult decisions about how best to prevent future cancers and how often to have examinations for detecting the cancers as early as possible. Their options include more frequent clinical breast exams and mammography, tamoxifen therapy, the preventive removal of the contralateral (other side) breast, the preventive removal of the ovaries, or various combinations of these options.

Women with BRCA1 mutations have an estimated lifetime risk of developing breast cancer of about 50 percent, while women with BRCA2 mutations have an estimated lifetime risk of 50 to 60 percent. That compares to about 12 percent in the general population.

The JAMA study looked at how life expectancy might be affected based on a woman’s particular type of BRCA1 or BRCA2 mutation, her age at diagnosis, and whether or not there was axillary lymph node involvement.

The researchers found that preventive mastectomy (prophylactic contralateral mastectomy, or PCM) and, to a lesser extent, preventive removal of the ovaries (prophylactic oophorectomy, or PO), and tamoxifen may "substantially increase life expectancy for young women with early-stage breast cancer and moderately or highly penetrant BRCA1/2 mutations."

"In contrast, young women with sporadic breast cancer (not associated with the genetic mutations) gain less than two months’ life expectancy from PCM and less than two weeks from PO," the authors wrote.

The study provides a very useful tool to help women and their doctors make decisions about treatment, according to Robert Smith, PhD, director of cancer screening for the American Cancer Society (ACS).

"Only about one in 800 women are believed to carry a significant mutation on BRCA1, but women with inherited mutations are at significant risk for breast cancer throughout their lives," Dr. Smith said. "The models developed by Dr. Schrag and her colleagues provide a very useful tool to help these women and their physicians reach decisions about the value and appropriateness of any one or a combination of the risk reduction options available today."

According to Dr. Smith, more must be learned about the growing number of genetic mutations that are being identified and the effectiveness of preventive options. "However, the estimates from this model should reduce uncertainty in decision making and provide women at high risk with greater confidence about their choices," he said.

One very important aspect of this study is that the impact of cancer prevention strategies is based on information about each woman’s individual medical situation. For example, preventive removal of the noncancerous breast and both ovaries, together with the drug tamoxifen, extends life for women with high-penetrance mutations and node-negative breast cancer an average of 4.4 years. The figure for women with low-penetrance mutations and node-positive breast cancer is much lower – less than one month.

In considering this information, women should realize that no operation or drug can guarantee an extra 4.4 years of life, or even an extra month. All of these numbers are averages. Some women in each category will avoid cancers that might have been lethal at an early stage and may gain decades of added life. Other women may have never developed another cancer and these preventive measures would not affect their lifespan. And, a few women who have these operations or take tamoxifen may nonetheless develop a fatal cancer because none of these preventive measures is 100 percent effective.