The most common type of breast cancer starts in the lining of the breast ducts and is called ductal carcinoma.
Breast cancer that has not spread outside the ducts is called intraductal breast cancer or ductal carcinoma in situ. This type of cancer is noninvasive breast cancer. When breast cancer is noninvasive, it has not spread to other parts of the body. Noninvasive breast cancer is often cured with surgery, although other treatments may be recommended.
Invasive ductal carcinoma has spread outside the breast ducts. Invasive breast cancer may be treated with surgery, sometimes together with radiation. Treatment for invasive breast cancer may also include chemotherapy or hormonal therapy.
When breast cancer spreads, cancer cells may also be found in the lymph nodes in the armpit. These lymph nodes are called axillary lymph nodes. If the cancer reaches these nodes, it may have spread to other parts of the body. This is also an indicator of risk of recurrence.
Breast cancer that has spread to other organs of the body is called metastatic breast cancer. When breast cancer spreads to other parts of the body, it most often goes to the brain, bones, liver, or lungs.
Doctors are not sure why breast cancer behaves the way it does, or why it spreads in one woman and not in another. The way cancer behaves depends on many factors, some of which doctors do not yet know.