Breast cancer gene risk may vary widely, study shows

The risk of developing breast cancer in women found to have mutations in their BRCA1 or BRCA2 genes may vary significantly, according to a study published in the Journal of the American Medical Association last week. The researchers, based at Memorial Sloan-Kettering Cancer Centre, found that a carrier's risk of developing cancer by the age of 70 varies from 36 to 52 per cent - a range significantly less than the 80 percent lifetime risk currently cited in medical guidelines.

Lead author Dr Colin Begg said that the results supported the idea that BRCA1 and 2 carriers are not guaranteed to get breast cancer. 'The risks in carriers and relatives must be influenced by other risk factors,' said Dr Begg.

The lifetime risk of breast cancer for women who inherit a mutated BRCA1 or BRCA2 gene can be as high as 85 per cent according to previous studies. But the extent to which this risk varies among carriers - a factor necessary to aid decision making in cancer prevention - has not been widely studied, say the researchers.

Of 2098 women who had been diagnosed with breast cancer before the age of 55, the researchers identified 181 who had either BRCA1 or BRCA2 mutations. They then examined these women more closely to see if any of their close relatives - parents, siblings or children - had also been diagnosed with breast cancer, or whether they had developed separate cancers in both breasts.

They found that close relatives of women diagnosed with breast cancer before the age of 35 themselves had a 52 per cent risk of developing breast cancer by the age of 70, compared to a risk of 36 per cent if women are diagnosed after 45. Between the ages of 70 and 80, the breast cancer risk rose to 90 per cent in relatives of women diagnosed aged under 35, compared to 44 per cent in relatives of women diagnosed after 45.

Dr Begg believes that future studies will reveal other breast cancer genes, helping to explain the variation in risk between BRCA carriers. 'There's a lot of research going on at the moment in general to find additional breast cancer genes. What we're saying here is that research is likely to be successful', Dr Begg told Reuters.

In the future, as our understanding of the genetic basis of breast cancer increases and the cost of genetic testing falls, this may raise the prospect of population-wide screening leading to personalised treatment and prevention plans, wrote the researchers.