The study is being called the most comprehensive to date of women with inherited mutations of the BRCA1 and BRCA2 genes. These genes are cancer suppressor genes, and women with mutated forms do not suppress tumor growth and have an increased risk of ovarian or breast cancer. The study appears in this week's edition of the journal Science, and it illustrates the need for more research in breast cancer prevention.
"It was a surprise, but a source of hope, to learn that factors over which we have some control made a difference in the age at which these highest-risk women developed breast cancer," says lead researcher Mary-Claire King, PhD, professor of genome sciences and medicine at the University of Washington in Seattle, in a news release.
Secrets of Teenage Lifestyle
Other breast cancer research has shown wide variations in estimated risk of breast cancer among women with BRCA1 and BRCA2 mutations. Overall, the lifetime risks of women developing breast cancer is about 10%; in women with these mutations the lifetime risk of developing breast cancer is thought to be in excess of 80%.
To better understand this phenomenon, King and her research team looked at a variety of lifestyle factors and the BRCA1 or BRCA2 gene type in more than 1,000 women with a history of breast cancer recruited at 12 major cancer centers in New York City.
Of the 1,008 women found to have breast cancer, 104 had a BRCA1 or BRCA2 mutation.
What the researchers found in this study was that 50% of the women who carried the mutation did not have a history of breast or ovarian cancer in their immediate family because the mutation had come from their father. "If a family is small, there may be no warning that a mutation is present," says King.
The study showed that those with the BRCA1 or BRCA2 mutation had a 20% risk of breast cancer by age 40, a 55% risk by age 60, and more than 80% by age 80 -- an overall 82% risk of cancer in their lifetime, reports King.
But after factoring in exercise and body weight, researchers discovered that these two factors indeed delayed the age of onset of breast cancer in those with the inherited mutations. Those who were physically active developed breast cancer later than those who were physically inactive.
The study also showed that normal weight and lighter weight at age 21 was associated with an older age of breast cancer onset.
Those women who were physically active and kept a healthy weight as teenagers developed breast cancer later than other women, King reports.
Prevention Research Needed
This new breast cancer research adds another preventive measure to a growing list, which includes screening starting at an early age, prevention drugs such as tamoxifen, and risk-reducing surgeries of the breast, King says.
The findings apply to all women: Other breast cancer research has shown that exercise and healthy weight in early life are protective against breast cancer after menopause, she reports.
Indeed, a variety of factors such as dietary, reproductive, hormonal, and environmental factors likely influence the effect of these mutated genes on cancer risks. Extensive breast cancer research is needed on all these factors, writes Ephrat Levy-Lahad, with the Medical Genetics Unit at Hebrew University in Jerusalem, in an accompanying editorial.