Some women with genetic mutations had their breasts removed after studies showed they had a high risk of developing breast cancer during their lifetime. But a new analysis suggests the risks may have been exaggerated.

Researchers reviewed eight population-based studies on breast cancer risk from breast cancer gene mutations, called BRCA1 and BRCA2. Early studies estimated the lifetime breast cancer risk for women with the mutation and family history of breast cancer at between 71 and 85 per cent.

Dr. Colin Begg of Memorial Sloan-Kettering Cancer Center in New York said the high risk rate is inflated and cannot be applied to every woman with a BRCA gene mutation.

Breast cancer risks from mutations may have been inflated

Begg said the studies were flawed because they did not account for the increased prevalence of other risk factors among breast cancer patients and their sisters, mothers and grandmothers.

Doctors can't predict risk for an individual woman

More recent studies have shown the breast cancer risk among mutation carriers varies widely, and the average risks are lower than those that have been quoted.

Some women have had preventative mastectomies

"We don't know at the moment how to predict risks well for the individual," Begg said.

Dr. Kathy Helzlsouer, an epidemiology professor and medical oncologist at Johns Hopkins University in Baltimore, said doctors and genetic counsellors have realized how uncertain cancer risk calculations are among women with BRCA gene mutations.

Some women may have chosen to have their breasts removed based on the exaggerated data that was available at the time. Others may have decided to take drugs such as tamoxifen to lower the risk, or do nothing.

"Without a healthy respect for the many factors that may influence penetrance, we will continue to overestimate the risk conferred by BRCA1 and BRCA2 mutations alone," wrote Drs. Wylie Burke and Melissa Austin, from the University of Washington, Seattle, in an editorial.

"And thus, (we may) miss opportunities to develop truly effective strategies for women who are genetically susceptible to breast cancer."

The study and commentary appear in the Aug. 21 issue of the Journal of the National Cancer Institute.