Issues in Radiation Treatment for Breast Cancer

By Diane Severin MD

Background

When a woman has surgery for breast cancer, the presence of cancer cells in the lymph nodes in the armpit (called 'lymph node positive') means that there is a high chance that cancer cells are elsewhere in the body. These cancer cells are usually in small numbers and are such a small size they cannot be found by X- rays or scans. Women who have positive lymph nodes are normally advised to receive systemic treatment (chemotherapy) as well as radiation therapy.

If more than four lymph nodes in the armpit were found to have cancer cells, women will be advised to receive radiation treatments to the armpit (also called 'axilla'), supraclavicular fossa (the area above the collarbone) and / or the internal mammary chain (the area between the ribs and breastbone). These are areas where many lymph nodes are located (see picture).

1. humerus (the bone in the upper arm)
2. clavicle (or collarbone)
3. supraclavicular fossa (area of lymph nodes above the clavicle)
4. axillary lymph nodes (lymph nodes in the armpit routinely removed with surgery)
5. internal mammary lymph node chain

The goal of giving radiation treatment is to decrease the chance of cancer coming back (called a local recurrence) in the armpit area, other lymph node areas, and the chest wall. Patients who have had more than 10 lymph nodes removed may have radiation to the supraclavicular area only, as the incidence of recurrence in the armpit is small (2-3%).

Giving radiation treatment to the internal mammary chain has been controversial and remains so. Recurrence in this area is rare (5%) but in cases where the internal mammary nodes were examined under the microscope, there was an increased chance of finding cancer cells if cancer cells had also been found in the axillary nodes.

Radiation and Mastectomy Studies

The treatment of the internal mammary nodes has become more common, but controversy continues since the 1997 publication of three randomized trials studying post-mastectomy radiation. Women with breast cancers considered high risk because of large tumor size or positive lymph nodes were randomized to receive:

• chemotherapy or tamoxifen versus
• chemotherapy or tamoxifen and radiation therapy

All the women who took part in the three studies had mastectomies (the entire breast removed by surgery). The area radiated was the chest wall, axilla (if less than 10 lymph nodes were removed), supraclavicular fossa and internal mammary chain. These studies included both pre-menopausal and post-menopausal women. Patients were examined by their doctors regularly for ten years after treatment. The patients who received radiation treatment were found to have a decrease in local recurrence as well as a survival benefit of 9%. This has not been shown before in a randomized trial. After the publication of these three studies many oncologists felt there was enough evidence to offer radiation therapy to all women who had mastectomies and had high risk of recurrence or positive lymph nodes.

Not all oncologists agree with this and argue that the women who took part in these studies do not represent the same type of patients seen in their practice. The reason for this is the relatively small number of lymph nodes removed from the axilla (median of 7 nodes) in two of the studies. In North America, most surgeons remove ten or more lymph nodes from the axilla. The argument is that the patients in these 2 studies benefited from the radiation because these had been cancer cells left behind in the axilla.

Radiation and Breast Conservation

The area of controversy is whether or not to give radiation treatment to the lymph nodes including the internal mammary chain for women who have undergone lumpectomy (the breast is conserved and only the part of the breast containing the tumor was removed with surgery). Radiation to the conserved breast is considered standard treatment and is known to decrease local recurrence but has never shown a survival benefit. The supraclavicular area and/or the axilla are usually radiated only if:

• 4 or more axillary lymph nodes are positive for cancer cells or
• less than ten nodes were removed and one or more of these is positive

Whether or not to treat the internal mammary nodes is unclear. Since the three post-mastectomy trials were published, the question is whether or not radiation treatment to the lymph nodes in patients with lumpectomies would also give a survival benefit. Unfortunately, the results of the post-mastectomy trials cannot be applied to women who have had breast conservation. The reason for this is that breast conservation patients and post-mastectomy patients are two different populations. The prognosis of a patient who has a local recurrence in the conserved breast is much different than that of a patient with a local recurrence post-mastectomy. No randomized trials have been published addressing this issue.

The Study at the Cross Cancer Institute

The National Cancer Institute of Canada (NCIC) is currently trying to answer this question - is radiation to the lymph nodes helpful for women who have had breast conservation and are lymph node-positive? Patients are being randomized to receive radiation to the breast only as per standard practice or radiation to the breast and lymph nodes (axilla - if less than 10 nodes removed, supraclavicular fossa and internal mammary chain). Again, the results of this study will not be available for many years. You can find out more about this and other studies at the Cross Cancer Institute on our Research page. You may also contact the research nurses Liz Shepert at 432-8802 or Janet Samson at 432- 8546.

Sources

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