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Breast cancer risk: not all in the family

Breast cancer Women do not automatically have a higher risk of getting breast cancer just because someone else in the family has tested positive for breast cancer genes, say US researchers.

The findings may bring comfort to women from high-risk families after a 2007 study suggested that simply having a relative with a BRCA1 or BRCA2 mutation raised their risk of developing breast cancer, even if they themselves tested negative for the genes.

"The results are encouraging and reassuring," says Dr Allison Kurian of Stanford University School of Medicine, whose study appears in the Journal of Clinical Oncology.

Some 5 per cent to 10 per cent of breast cancers are genetic, and most of these cases are caused by abnormalities in the BRCA1 or BRCA2 genes.

Women with these mutations have a five to 20 times higher risk of developing breast or ovarian cancer, and must undergo intensive cancer screenings and take other precautions to reduce their cancer risk.

Many of these women elect to have their breasts or ovaries removed to keep from developing cancer.

Once these mutations turn up in a family, other family members are screened as well. Women from these families who test negative have traditionally been told they have about the same risk as women in the general population.

But a 2007 study published in the Journal of Medical Genetics challenged that notion, suggesting that even though women in high risk families did not carry breast cancer genes, they still had a two to five times higher risk of developing breast cancer.

That created a considerable amount of anxiety among doctors and patients, says Kurian.

Study of families

To study this, her team analysed data on more than 3,000 families with BRCA1 or BRCA2 mutations from three countries: the United States, Canada and Australia.

They compared breast cancer rates among carriers and non-carriers of family mutations of the BRCA1 and BRCA2 genes.

They found no evidence of an increased breast cancer risk among women who were non-carriers.

"It's reassuring that we don't see a signal for elevated breast cancer risk from women who test negative for a familial mutation," says Kurian.

Co-author, epidemiologist Professor John Hopper, of the University of Melbourne, says the 2007 study was "misleading" because it was not properly designed and there problems with the interpretation of the data.

"The study was done by clinicians who might be very good at diagnosing disease and telling you the right treatment but they're not trained in epidemiology and statistics," says Hopper.

"The 2007 study was very alarming and caused concern for the genetic counsellors who had been advising women from families like that. So it's been very important that we've now been able to do proper studies."

Geneticist, Professor Rodney Scott of the University of Newcastle says he is not surprised that the 2007 study had been counteracted.

"People felt the [2007] study itself was somewhat small and one needed to do a larger study," says Scott.

He says the most recent study is larger and its findings are in line with "what everyone intuitively thought before".

"It certainly should reassure women from such families who do not carry a BRCA1 or BRCA2 mutation that their risk of developing breast cancer is no different to that of the general population."