Giving radiation therapy to the lymph nodes located behind the breast bone and above the collar bone to patients with early breast cancer improves overall survival without increasing side effects. This new finding ends the uncertainty about whether the beneficial effect of radiation therapy in such patients was simply the result of irradiation of the breast area, or whether it treated cancer cells in the local lymph nodes as well. This finding was presented at the 2013 European Cancer Congress.

Lymphatic drainage from breast cancer means that the cancer is more likely to spread to other parts of the body. It normally follows two pathways. The best known is to the axilla, and these lymph nodes are usually treated by surgery and/or radiation therapy. The second pathway drains to the internal mammary (IM) lymph nodes behind the breast bone, and also to those just above the collar bone, the medial supraclavicular (MS) nodes. Because of uncertainty about the effects of treatment in this area, and particularly concerns about the increased toxicity that might be due to the irradiation of a larger area, many centers do not currently treat the IM-MS lymph nodes.

“Our results make it clear that irradiating these lymph nodes give a better patient outcome than giving radiation therapy to the breast/thoracic wall alone. Not only have we shown that such treatment has a beneficial effect on locoregional disease control, but it also improves distant metastasis-free survival and overall survival,” said Philip Poortmans, MD, PhD, of the Institute Verbeeten, Tilburg, The Netherlands, and a member of the EORTC Radiation Oncology and Breast Cancer Groups. This international randomized trial involved 4,004 patients from 43 centers.

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After an average follow-up of 10.9 years, patients in the IM-MS treatment group had better overall survival independent of the number of lymph nodes involved. A total of 382 patients in the IM-MS group died during that period, compared with 429 in the non IM-MS group, and there was no increase in mortality not related to breast cancer in the first group. To date, no serious complications related to the treatment have occurred.

The researchers believe that the beneficial effect of IM-MS radiation can be explained by the ability of the treatment to eradicate microscopic tumour deposits in the lymph nodes. “With this treatment, we can stop the development of metastases at their source,” said Poortmans. “Interestingly, this effect is irrespective of the stage of the tumor. We believe that this is likely to be related to the positive interaction of the IM-MS treatment with systemic treatment—chemotherapy, hormonal therapy, and targeted treatment.”

“The results of our trial, in which the patients received appropriate systemic treatments, contradict the existence of a ‘competition’ between locoregional and systemic treatments,” said Poortmans. “Because there is an interaction between these treatments, in many patients their combination will result in an enhancement of the combined benefits; in other words, one plus one can equal more than two.”