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 more 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.

Based on the findings by the pathologist, if the tumor is cancerous (malignant) then additional tests, such as an MRI, ultrasound or PET scan may be ordered. All these tests provide the physician with additional information as to the location and stage (extent of spread) of the cancer and other information about the tumor and how it may respond to treatment. 

There are several options for breast surgery ranging from the breast-sparing lumpectomy to the now rarely used Halsted radical mastectomy, which removes the breast, the chest muscles and nearby lymph nodes.

In addition to surgery, a patient may receive additional treatment based on the type of breast cancer, its size and other important factors. The size of the tumor, the possible spread of the cancer to the lymph nodes and any possible spread to other organs or tissues helps the oncologist (cancer physician) determine the stage of the cancer. This information, in turn, gives the physician the necessary input to select the best treatment options for the patient. These options can include a wide variety of combinations of treatment, including surgery, radiation therapy, chemotherapy, hormone therapy or biological therapy.

A major study released in 2006 indicated that the number of new cases of breast cancer dropped significantly in the reporting period of 2002 to 2003. The ACS has reported a leveling off of new cases from 2001 to 2003, after 20 years of increases.

Overall survival rates for breast cancer are quite high when the disease is detected and treated in its earliest stages. When breast cancer progresses undetected to later stages, the survival rates drop. The 5-year survival rate for cancer that is localized (not spread to the lymph nodes or areas outside of the breast) is 98 percent. If the cancer has spread to nearby tissues, the 5-year survival rate is 83 percent.

According the ACS, large gains in survival rates for several cancers, including breast cancer, have been recorded over the past two decades. The overall survival rate for all stages of cancer at 5 years is 89 percent and at 10 years is 80 percent.