Narod said the researchers had hoped to see an even greater reduction in risk, because when they studied women with these genetic mutations after prophylactic removal of their breasts, none of the women developed breast cancer.
In the second study, researchers gathered information on weight status throughout the lives of more than 87,000 postmenopausal women in the Nurses' Health Study. The researchers found that weight gain, especially after menopause, can increase the risk of breast cancer, but that post-menopausal weight loss can reduce the risk of breast cancer.
"The good news is that it's never too late to lose weight to reduce your risk of breast cancer, but the best thing is to avoid weight gain in the first place," said the study's lead author, Heather Eliassen, an instructor in medicine at Brigham and Women's Hospital and the Harvard School of Medicine and Public Health, in Boston.
Results of these studies are in the July 12 issue of the Journal of the American Medical Association.
Narod's study included 1,828 women from Canada, the United States, Europe and Israel known to carry either the BRCA1 or BRCA2 mutation. Before the study began, 555 of the women had their ovaries and fallopian tubes removed. Another 490 women had them removed during the study period, while 783 did not have the procedure.
Thirty-two cases of ovarian cancer were found in the women who still had their ovaries intact. Just seven of the women who underwent the procedure were diagnosed with what appeared to be ovarian cancer, Narod said.
The cancers that developed in the women who'd had their ovaries removed occurred in the peritoneum, the lining of the abdomen. Narod said this tissue is similar to ovarian tissue. Unlike the ovaries, the peritoneum cannot be removed.
The researchers estimated the cumulative 20-year risk of ovarian cancer for women who have had their ovaries removed at about 4 percent. Without the procedure, about 40 percent of women with the BRCA1 mutation can expect to develop ovarian cancer. For the average woman, the rate is about 1.4 percent over a lifetime, Narod said.
Dr. Jay Brooks, chairman of hematology/oncology at the Ochsner Clinic Health System in Baton Rouge, La., said, "If you have a BRCA mutation, and you have not had your ovaries and uterus removed, they need to be removed once you have completed childbearing. It's the single greatest thing to do to reduce ovarian-cancer risk, and it reduces the risk of breast cancer, too."
From the large group of women involved in the Nurses' Health Study, Eliassen and her colleagues discovered 4,393 cases of invasive breast cancer. When they looked at the effect of weight changes that had occurred since these women were 18 years old, the researchers saw a definite link between weight and breast-cancer risk.
In fact, the researchers concluded that 15 percent of these breast-cancer cases might be attributable to weight gains of just 2 kilograms or more since age 18. Two kilograms is about four-and-a-half pounds.
Women who gained 55 pounds or more had almost a 50 percent higher risk of developing breast cancer than women who had maintained their weight. Those who gained about 22 pounds since the age of 18 had about a 20 percent higher risk of breast cancer.
The good news from this study, however, was that women who lost 22 pounds or more after menopause and kept the weight off reduced their risk of breast cancer by nearly 60 percent.
Eliassen said that after menopause, the hormone estrogen is made primarily in fat tissue, and the more fat you have, the more estrogen your body will produce. This can increase breast-cancer risk, because many breast cancers are fueled by estrogen.
More information
To learn more about risk factors for cancer, visit the National Cancer Institute. |
