A retrospective analysis on metastatic rate of the internal mammary lymph node and its clinical significance in adjuvant radiotherapy of breast cancer patients

BACKGROUND: There is a discrepancy about the metastatic rate of internal mammary lymph nodes (IMNs) between clinical and pathologic findings. We aimed to investigate the metastatic rate of IMNs and to provide recommendations on target volume delineation of IMNs for adjuvant radiotherapy in breast cancer patients. METHODS: We retrospectively analyzed data from 114 breast cancer patients treated with surgery without adjuvant radiotherapy who developed local and/or regional lymph node recurrence/metastasis at our institute from January 2015 to January 2019. Patients with widely lung or pleural metastases were excluded. We first analyzed the recurrence rate with the chest wall, the metastatic rate of internal mammary/anterior mediastinal, ipsilateral axillary and supraclavicular lymph nodes, and then investigated the distribution of the IMNs. RESULTS: Among the 114 included patients, the recurrence rate with the chest wall, metastatic rate of IMNs, IMNs/anterior mediastinal lymph nodes, ipsilateral axillary lymph nodes, and the ipsilateral supraclavicular lymph nodes was 43, 37.7, 59.6, 12.3, and 22.8%, respectively. The metastatic IMNs were mainly located from the first to the second intercostal space. However, metastatic lymph nodes could also be observed above the upper edge of the first rib. CONCLUSIONS: The metastatic rate is high in the IMNs and irradiation of the internal mammary lymphatic chain is required. It is suggested that the upper bound of the internal mammary lymphatic chain should be up to the subclavian vein with a 5-mm margin, thus connecting to the caudal border of supraclavicular clinical target volume in breast cancer patients at high risk of recurrence.