Two large studies provide a much clearer picture of inherited mutations that increase the risk of breast cancer in women without a family history of the disease and how common these defective genes are in the general population.
Doctors say the results, published Wednesday in the New England Journal of Medicine, may help women make better decisions about screening, preventive surgery or other steps.
Although this type of genetic testing is not currently recommended for the general population, its use is increasing and many people are receiving it from tests sold directly to consumers.
The new paper shows that the risk posed by some genes “is very high,” wrote Mary-Claire King in an e-mail. King, a scientist at the University of Washington, had no role in the new studies, but he discovered the first predisposing gene for breast cancer, BRCA1.
“Many women’s lives could be saved if all women were given the opportunity to find out if they had mutations in these genes before they were diagnosed with cancer,” she wrote.
The American Cancer Society estimates that 276,000 new cases of breast cancer were diagnosed in the United States last year. The new paper suggests that at least 13,800 of these occur in women with inherited genetic mutations that increase their risk of developing the disease.
So far, what is known about inherited risk has come largely from studies of women with a family history of breast cancer or unusual situations, such as getting it at a very young age. There has also been little work on specific mutations in these genes and how much each affects the chances of developing the disease. New studies fill some of these gaps.
One was led by Fergus Couch, a pathologist at the Mayo Clinic, and included researchers from the National Institutes of Health, who sponsored the study with the Breast Cancer Research Foundation.
They looked for possible mutations in 12 genes that were linked to breast cancer in more than 64,000 women, about half with the disease and half without it, combining the results of studies in the United States, including some specific minority groups such as blacks. .
They found annoying mutations in about 5% of women with the disease and in 1.63% of the comparison group.
“We now realize that 2% of women walking in the United States could have mutations in these genes,” Couch said.
There were no differences between racial groups in terms of the chances of having a general mutation, but some mutations were more common in some groups. For example, women of color were more likely to have those related to “triple negative” cancer – tumors that are not fed estrogen or progesterone or the gene that targets the drug Herceptin.
The study also found that a mutation in the BRCA1 gene increased the risk of developing breast cancer almost eight times, and in the BRCA2 gene, more than five times.
On the contrary, another gene was considered very worrying, but “what I found is that it’s really low risk … people shouldn’t act on it,” Couch said.
Actions could include more frequent mammograms or other screening tests, removal of breasts or ovaries, testing of family members or other steps.
With the new paper, “we provide more accurate risk estimates” to guide such decisions, Couch said.
The second study, conducted by researchers at Cambridge University in England, looked at 34 genes in women in the UK, Europe, Australia and Asia – about 60,000 with breast cancer and 53,000 similar without it.
“They found what we found – increased risk from certain genes and a similar prevalence of them in the general population,” Couch said.
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