What is Staging?

"Staging" is the word used to describe various examinations, usually done after a more advanced type of cancer is diagnosed, to see if the disease is still localized or has spread to other places in the body. For example, surgery to remove some of the axillary lymph nodes in the armpit is a staging procedure.
In dealing with breast cancer, the whole point of doing a mastectomy is to remove the cancer while it's still confined to the breast. (If a second malignant tumor is found later in the other breast, this is usually a "new primary", not a metastasis from the first). If the cancer is already known to be present in other parts of a woman's body, removing her breast has limited or no benefit unless it's infected, painful or ulcerated. The need for staging when advanced cancer is found is another important reason for separating diagnosis from treatment - to avoid more surgery than is necessary.
No staging technique is 100% reliable; but certain blood tests, X-rays, nuclear and "CT" (computed tomography) X-ray scans can often show if the cancer has spread to the bone, lungs and the liver. Brain scans aren't routinely done as a part of staging unless the patient has neurological symptoms or results of other exams are suspicious, but preoperative bone scans and/or X-rays are still ordered by most experts.
However, a woman facing a mastectomy for a large breast cancer tumor should ask for a bone scan before permitting her breast to be removed.