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Breast Cancer

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What is breast cancer?

Breast cancers are malignant tumors that arise from the uncontrolled growth of cells in the breast. They occur primarily in the ducts that transport milk to the nipple during breast feeding (lactation) and secondarily in the lobules, the glands that produce milk.

Thumbnail diagram of the breast

Each breast cancer will have its own characteristics. Some are slow-growing; others can be aggressive. Some are sensitive to the hormones estrogen and progesterone, while others can over-express certain proteins. The cancer's characteristics can affect treatment choices and the potential for the cancer to recur.

Each year, more women in the United States are diagnosed with breast cancer than with any other cancer, with the exception of skin cancer. About 1 in 8 American women will develop invasive breast cancer in their lifetime. The American Cancer Society (ACS) estimates that about 230,000 new cases of invasive breast cancer will be diagnosed in women in the U.S. in 2015 and that about 40,000 women will die from the disease. Men can also develop the disease. ACS estimates that about 2,300 men will be diagnosed with breast cancer in 2015, and about 440 men will die. The rest of this article will focus on breast cancer in women. It is recommended that men who have been diagnosed with breast cancer speak to their healthcare provider for information specific to them and see the ACS's web site about Breast Cancer in Men.

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