CausesBy Mayo Clinic staff
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|How cancer develops|
It's not clear what causes breast cancer. Doctors know that breast cancer occurs when some breast cells begin growing abnormally. These cells divide more rapidly than healthy cells do. The accumulating cells form a tumor that may spread (metastasize) through your breast, to your lymph nodes or to other parts of your body.
Breast cancer most often begins with cells in the milk-producing ducts. Doctors call this type of breast cancer invasive ductal carcinoma. Breast cancer may also begin in the milk glands known as lobules (invasive lobular carcinoma) within the breast.
Researchers have identified things that can increase your risk of breast cancer. But it's not clear why some people who have no risk factors develop cancer, yet other people with risk factors never do. It's likely that breast cancer is caused by a complex interaction of your genetic makeup and your environment.
Inherited breast cancer
Doctors estimate that only 5 to 10 percent of breast cancers are linked to gene mutations passed through generations of a family. A number of inherited defective genes that can increase the likelihood of breast cancer have been identified. The most common are breast cancer gene 1 (BRCA1) and breast cancer gene 2 (BRCA2), both of which increase the risk of both breast and ovarian cancer.
If you have a strong family history of breast cancer or other cancers, blood tests may help identify defective BRCA or other genes that are being passed through your family. Consider asking your doctor for a referral to a genetic counselor, who can review your family health history. A genetic counselor can also discuss the benefits, risks and limitations of genetic testing with you. It's important to remember that the genetic tests help to identify a high-risk individual or family, but they don't definitively predict who will or will not get breast cancer.
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