The study focused on women at five institutions who had tested positive for a mutation of the BRCA1 gene, a condition linked to a high risk of breast cancer, said Timothy R. Rebbeck of the University of Pennsylvania School of Medicine.
He is first author of a study that in the Journal of the National Cancer Institute.
Forty-seven of the women studied had undergone surgery to remove both ovaries, while another 79 women had the gene mutation, but not the surgery.
Rebbeck said that among those who had ovarian surgery, there was a 67 percent reduction in the incidence of breast cancer after 10 years. In women followed between five and 10 years, the risk reduction was about 72 percent.
"This is helpful, but it is a small study," said Dr. Lynn C. Hartmann, a cancer specialist at the Mayo Clinic. "It clearly needs to be taken with some caution."
The BRCA1 gene mutation is thought to be a factor in a small percentage of both breast and ovarian cancer cases nationally, but among women with the mutation their chances of developing the diseases is very high, Rebbeck said.
For women with the mutation, plus a family history of breast cancer, the lifetime risk of breast cancer can be as high as 80 percent, he said. For ovarian cancer, the risk can be 40 percent to 50 percent, Rebbeck said.
Medical science has been struggling to find the best way to treat such women and to determine who should be tested for the BRCA gene mutation.
Among the options being studied and practiced are preventative mastectomy and the use of drugs that appear to lower the incidence of breast cancer among women at high risk. Removing the ovaries has been used to reduce the ovarian cancer risk, but some experts believed the surgery also would reduce the risk of developing breast cancer by limiting hormones that can encourage tumor growth. That is the issue addressed in the study.
"This is the first study demonstrating a surgical approach to breast cancer risk reduction among BRCA1 mutation carriers," Rebbeck said. Although only a small percentage of women have the mutation, he said, the findings may help doctors and patients make decisions about how to deal with risks posed by the mutation.
Another mutation, BRCA2, also has been linked to breast cancer but affects fewer women. Only the BRCA1 mutation was included in the study.
Out of about 183,000 breast cancers diagnosed annually, only 5,000 to 9,000 can be linked to the BRCA1 mutation, he said.
But Rebbeck said women who have a family history suggesting a high risk, such as a mother or sister who developed breast or ovarian cancer at an early age, should talk to genetic counselors for help evaluating their medical options.
He said removing the ovaries does not completely eliminate the risk of breast cacer. And, said Rebbeck, the surgery brings on menopause which carries some increased risk of osteoporosis and heart disease.