Introduction

Breast cancer is the most common form of cancer in women. It will account for an estimated 26 percent of all cancer diagnosed in women in 2010, according to the American Cancer Society. Over the course of a woman's life, she has a 1 in 8 chance of getting the disease. It is also possible for men to develop breast cancer, although this is rare.

In breast cancer, cells in the tissue of the breast grow without stopping. These out-of-control cells form masses (lumps) called tumors. Malignant (cancerous) tumor cells may then spread to other parts of the body. 

Breast cancer may be limited to the area where it first developed, especially in the earliest stages. At that time it is easiest to cure. In later stages of breast cancer, breast cancer may invade surrounding tissues or spread to more distant parts of the body. Regular screening followed by prompt diagnosis and treatment are needed to prevent breast cancer from spreading (or spreading further) and to eliminate the cancer.

Other names for cancer of the breast are mammary cancer, breast carcinoma (carcinoma of the breast), and adenocarcinoma of the breast. The breasts are glands that release female hormones important for reproduction. They normally contain many glandular cells.

The exact causes of breast cancer are not known. Risk factors associated with developing breast cancer include family history (having a close relative, such as a mother or sister with breast cancer) and heredity (having certain genes associated with breast cancer). Other risk factors include smoking, physical inactivity, a high-fat diet, obesity, and long-term use of estrogens, and progesterone (hormone replacement therapy) after menopause.