Breast cancer is a disease in which malignant (cancer) cells form in the tissues of the breast. There are four types of standard treatment are used for breast cancer such as surgery, radiation therapy, chemotherapy and hormone therapy. Radiation therapy is a cancer treatment that uses high-energy x-rays or other types of radiation to kill cancer cells or keep them from growing. There are two types of radiation therapy. External radiation therapy uses a machine outside the body to send radiation toward the cancer. Internal radiation therapy uses a radioactive substance sealed in needles, seeds, wires, or catheters that are placed directly into or near the cancer. The way the radiation therapy is given depends on the type and stage of the cancer being treated. Chemotherapy is a cancer treatment that uses drugs to stop the growth of cancer cells, either by killing the cells or by stopping them from dividing. When chemotherapy is taken by mouth or injected into a vein or muscle, the drugs enter the bloodstream and can reach cancer cells throughout the body. Hormone therapy is a cancer treatment that removes hormones or blocks their action and stops cancer cells from growing.