Women with the breast cancer genetic mutations BRCA1 or BRCA2 are at least 10 times more likely to develop breast cancer than the average woman.
The new study found that women who do not have a genetic mutation, but are closely related to women who do have genetic mutations are at an average risk of developing the disease.
Professor John Hopper from the School of Population Health, University of Melbourne, who led the Australian component of the study, said some women in this scenario were worrying unnecessarily.
“Our study revealed that these women have an average risk of developing the disease as opposed to the high risk of their mutation-carrying close relatives and hence do not need to worry unnecessarily and over screen to detect the disease,” he said.
“These findings go against a 2007 clinic-based study in the UK which claimed that all women in breast cancer families with known genetic mutations are at increased risk of developing the disease even if they don’t carry the family-specific mutation,” he said.
“Our results revealed there was no evidence of increased breast cancer risk for non-carriers of the genetic mutations, certainly not the five-fold increased risk suggested by the authors of the 2007 study.”
The international study is the largest analysis to date of breast cancer risk for non-carriers of family specific breast cancer mutations. It was led by Professor Alice Whittemore from Stanford University School of Medicine, USA and was published today in the Journal of Clinical Oncology.
More than 3000 breast cancer families from the population at large were analysed for their genetic risk of the disease. Researchers compared the risk of breast cancer among first-degree relatives of breast cancer patients who did and did not carry a BRCA1 or BRCA2 mutation.
Women were recruited from an international consortium, the Breast Cancer Family Registry, which used population cancer registries in USA, Australia and Canada. The Australian component involved the Australian Breast Cancer Family Registry, led by Professor John Hopper.
Professor Hopper said genetic testing could help to clarify which women are at high or average risk.
“Genetic testing will give women a clearer indication of their real risk level and hence clarify what they could or should not do to reduce their risks of developing beast cancer,” he said.
Women who think they might be at increased risk for breast cancer due to a strong family history of the disease can attend Family Cancer Clinics around Australia for genetic testing.
Contact Rebecca Scott,
University of Melbourne