For years, women with a rare gene mutation that puts them at higher risk for cancer have chosen to have their healthy breasts and ovaries surgically removed as a preventive measure.

New data on the subject, released today, suggest the surgeries do reduce a woman's risk of developing breast and ovarian cancers and improve her chances of living longer.

"It's just verifying what we already would expect to be true," said Dr. Matthew Powell, assistant professor of gynecology at Washington University School of Medicine. "Now we have longer-term follow up and more concrete numbers for our patients to really grasp."

The study is the largest to date to find advantages for preventive surgery for women who carry BRCA gene mutations (found in fewer than 1 percent of the general population).

Women with the faulty genes have a dramatically higher cancer risk than other women — five times greater for breast cancer and at least 10 times greater for ovarian cancer.

The study, appearing in today's Journal of the American Medical Association, found benefits for women with two different BRCA gene variants whether they had previously had breast cancer or not.

The results offer more tailored evidence for women considering ovary removal, a surgery that ends fertility, fast-forwards them into early menopause and may contribute to osteoporosis or heart problems later in life.

"It's really critical to have the best information when making such a profound decision," said senior author Timothy Rebbeck of the University of Pennsylvania School of Medicine.

The researchers followed nearly 2,500 women with BRCA mutations in Austria, England, the Netherlands and the United States. All the women were cancer-free at the start. They were watched for an average of four years. Most of the women were younger than 50 at the start of the study.

They got counseling to help them choose between surgery or increased screening to watch for cancers early.

Prophylactic mastectomies sharply reduce the risk of breast cancer by surgically removing the bulk of tissue where tumors can grow. Removal of the ovaries and tubes reduces the risk of ovarian cancer by removing most of the tissue in which it can arise and also lowers the risk of breast cancer by reducing the production of estrogen, which can fuel breast tumors.

Ten percent of the women in the study chose mastectomy and 40 percent chose to have their ovaries removed; some had both. More than half the women had neither surgery.

The women who chose ovary removal had impressive results:

• 1 percent were later diagnosed with ovarian cancer that showed up in cells missed by surgeons, compared with 6 percent of the women who kept their ovaries.

• 11 percent were diagnosed with breast cancer, compared with 19 percent of the women who kept their ovaries.

• 3 percent of those who had surgery died, compared with 10 percent of the others.

The study also found that preventive mastectomy lowered the risk of breast cancer. No breast cancers were seen in the women who had their breasts removed. That may seem unsurprising, but mastectomy can leave behind breast tissue that can turn cancerous.

The study was observational, meaning it can't prove one choice was better than another. Other factors could have caused differences in the cancer rates.

But the results will help doctors counsel their patients, said Dr. Virginia Kaklamani of Northwestern University's Feinberg School of Medicine in Chicago, who wrote an accompanying editorial in the journal.

"I'll use it mostly in talking to people considering genetic testing," Kaklamani said.

Powell, who works at the Siteman Cancer Center at Barnes-Jewish Hospital, said he saw three women on Tuesday who were affected by the abnormal gene. Breast removal may be considered any time after the presence of the genes has been diagnosed. For those women who decide against mastectomies, the alternative is more intensive screening, with a mammogram or MRI every six months.

Many physicians recommend ovary removal in BRCA carriers once they have completed their families because there simply is no good alternative.

"The issue we have with ovarian cancer is there's no good screening test," Powell said. "The only thing we know that protects a woman from cancer is removing the tubes and ovaries."

Blythe Bernhard of the Post-Dispatch contributed to this report, as did the Los Angeles Times and Associated Press.