Metastatic breast cancer, also known as advanced, secondary, or Stage IV breast cancer, is the spread of cancerous cell growth to areas of the body other than where the cancer first formed. This may happen before or after treatment of the cancer in the breast, or it may occur from a recurrent breast cancer (breast cancer that returns following a period where it could not be detected). Though breast cancer cells can spread to almost any part of the body, they most commonly spread to the bones. Other common sites include the lungs, liver, brain and skin. It is this new cancer that is called a metastasis.
You may be interested in the following CBCN publications on metastatic breast cancer: