Should internal mammary lymph nodes in breast cancer be a target for the radiation oncologist?

The elective treatment of internal mammary lymph nodes (++IMNs) in breast cancer is controversial. Previous randomized trials have not shown a benefit to the extended radical mastectomy or elective IMN irradiation overall, but a survival benefit has been suggested by some for subgroups of patients with medial tumors and positive axillary lymph nodes. The advent of effective systemic chemotherapy and potential for serious cardiac morbidity have also been factors leading to the decreased use of IMN irradiation during the past decade. The recent publishing of positive trials testing postmastectomy radiation that had included regional IMN irradiation has renewed interest in their elective treatment. The purpose of this study is to critically review historical and new data regarding IMNs in breast cancer.

The historical incidence of occult IMN positivity in operable breast cancer is reviewed, and the new information provided by sentinel lymph node studies also discussed. The results of published randomized prospective trials testing the value of elective IMN dissection and/or radiation are analyzed. The data regarding patterns of failure following elective IMN treatment is studied to determine its impact on local-regional control, distant metastases, and survival. A conclusion is drawn regarding the merits of elective IMN treatment based on this review of the literature.

Although controversial, the existing data from prospective, randomized trials of IMN treatment do not seem to support their elective dissection or irradiation. While it has not been shown to contribute to a survival benefit, the IMN irradiation increases the risk of cardiac toxicity that has effaced the value of radiation of the chest wall in reducing breast cancer deaths in previous randomized studies and meta-analyses. Sentinel lymph node mapping provides an opportunity to further evaluate the IMN chain in early stage breast cancer. Biopsy of "hot" nodes may be considered in the future to select patients who are most likely to benefit from additional regional therapy to these nodes.

Irradiation of the IMN chain in conjunction with the chest wall and supraclavicular region should be considered only for those with pathologically proven IMNs with the goal of improving tumor regional control.