Radiation is a “local” treatment like surgery. This means that it has an impact only where it is aimed, and it is usually limited to the breast (or chest wall) and lymph nodes.

Radiation is primarily given for three reasons. The first is to kill any microscopic cancer cells that might remain after a lumpectomy (also called a wide local excision or partial mastectomy). Even though the surgeon is able to get the entire tumor out with clear margins (meaning a rim of normal breast tissue around the cancer), we know that if we don’t give radiation to the breast, there is a significant risk that the tumor will come back in the breast. Radiation reduces this risk. Radiation in this situation can be given to the entire breast over several weeks (called whole breast irradiation) or it can be given with brachytherapy. Brachytherapy (also called accelerated partial breast irradiation or APBI) involves the placement of a balloon and catheter in the area of the breast where the tumor was located (the tumor bed). Radiation is given to just the tissue surrounding the tumor bed and not the whole breast. Not everyone qualifies for this treatment, but be sure to discuss whether or not you are a candidate with your surgeon and radiation oncologist.

The second reason that radiation is given is to reduce the risk of a recurrence in the chest wall or lymph nodes after a mastectomy. There are certain situations after a mastectomy that put you at increased risk for having the cancer come back. The first of these is a positive margin. Usually this means that the tumor was very close to the muscles of the chest wall so that when the surgeon removed the breast, some cancer cells were right at the edge. This means that some cells may have been left behind. Radiation is given to the chest wall and skin to kill these cells. Other reasons to give radiation after a mastectomy are that there were lymph nodes involved and/or the primary tumor was larger than 5 cm.

The third reason that radiation is given is to make a tumor resectable. Tumors that involve the skin or chest wall may be particularly difficult for a surgeon to resect with clear margins. In these instances, radiation may be given to shrink the tumor before surgery. However, it is probably more common to get chemotherapy in this situation and save radiation until after the surgery.