What Causes Breast Cancer?

A woman whose mother, sister, or daughter has had breast cancer is two to three times more likely to develop the disease, particularly if more than one first-degree relative has been affected.  Researchers have now identified two genes responsible for some instances of familial breast cancer. These genes are known as BRCA1 and BRCA2. About one woman in 200 carries the genes. Having one of them predisposes a woman to breast cancer but does not ensure that she will get it.

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