Breast cancer is a growth of abnormal cells within the breast. Breast cancer is not a single disease but rather a group of diseases that can develop in the ducts (which carry milk to the nipple), the lobules (milk producing areas) or other parts of the breast.

After non-melanoma skin cancer, breast cancer is the most common form of cancer in women. For 2007, the American Cancer Society (ACS) estimates that moreBreast cancer begins in the tissues, cells and ducts of the female or male breast. than 178,000 new cases of breast cancer will be diagnosed, adding to the 2 million women who have been diagnosed and treated previously for this disease. In addition, the ACS estimates that nearly 40,500 women are expected to die from breast cancer in 2007, making it the second leading cause of cancer death among women (surpassed only by lung cancer).

Although rare, men can also develop breast cancer. In the United States, about 2,000 men are expected to develop breast cancer in 2007, and about 450 men will die from the disease, according to the ACS. However, breast cancer primarily affects women.

Common ways to screen for breast cancer include monthly breast self-examination, clinical breast examination performed by a physician and screening mammography. However, to confirm a diagnosis of breast cancer, a biopsy is performed in which all or part of the mass is removed and then analyzed by a pathologist who views the specimen under a microscope.