The breast is considered the primary tumour site where the first cancer lump is diagnosed stemming from the breast duct or lobe. Breast cancer probably spreads through the bloodstream. The lymph nodes in the arms act as signals as to how likely a particular breast cancer is spread. Affected lymph nodes become swollen and enlarged.
When cancer comes back after treatment, it may return in the same place. This is called a “recurrence,” because it is not new cancer. But a recurrence can also appear in a place not directly related to the first breast cancer. This is called a “metastasis”. If cancer is detected in several areas, these are called “metastases” or secondary tumours.
Cancers from other parts of the body rarely spread to the breast or the chest wall. If you have a tumour in your lymph nodes, lungs, liver, bones, or brain, it probably is a re-growth or recurrence of the original breast cancer rather than a new and different cancer. In other words, if you had breast cancer and you now have cancer in your bones, liver, or other places, it is probably not bone or liver cancer, but breast cancer that has spread to the bones or the liver. This is important because breast cancer—even when it has spread—is usually more treatable than cancer that starts in the bones or liver.
Breast cancer that returns in other parts of the body is invasive cancer. However, cancer that comes back in the breast after surgery and/or radiation therapy can be either non-invasive or invasive. If you have developed cancer in the opposite breast from the one that was originally treated, it is probably not a recurrence. Most cancers that develop on the other side represent new cancer rather than a recurrence.
Breast cancer can return in three general locations. It can be:
- Local – in the breast where it started, or in the skin and underlying tissues where the breast used to be.
- Regional – in the lymph nodes next to the breast.
- Metastatic – in another part of the body, such as the lung, liver, bone, ovary or brain, or in lymph nodes far from the breast.
The spread of cancer is often termed as local, regional or distant.
- Local means that the spread of cancer is confined within the breast, even though there may be multiple sites in the breast.
- Regional means cancer has spread to the lymph nodes, mainly to the axillary nodes under the arm.
- Distant means that cancer has spread to other organs in the body.