Optimal radiotherapy for patients with internal mammary lymph node metastasis from breast cancer

BACKGROUND: This study aimed to determine the optimal radiotherapy (RT) regimen for patients with clinical metastasis to the internal mammary lymph node (cIMN+) from breast cancer. METHODS: We retrospectively reviewed the medical records of 84 patients with cIMN+ breast cancer treated with curative surgery, taxane-based chemotherapy, and postoperative RT between January 2009 and December 2014. Postoperative RT was administered to the whole breast or chest wall using 50 Gy in 2 Gy fractions. Boost RT to the internal mammary lymph node (IMN) was administered at the physician’s discretion. We categorized patients into two groups according to the IMN dose as follows: low-dose IMN RT (50.0–63.5 Gy) and high-dose IMN RT (63.6–70.4 Gy). RESULTS: After a median follow-up of 58 months (range, 12–111 months), IMN recurrence was observed in 2 patients (2.4%), and all IMN recurrences developed simultaneously with distant metastases. The 5-year locoregional recurrence-free survival, disease-free survival (DFS), and overall survival rates were 89.1, 72.0, and 81.2%, respectively. The triple-negative subtype, IMN size ≥1.0 cm, old age, and low-dose IMN were significantly associated with poor DFS. Among the patients with IMN size ≥1.0 cm, the 5-year DFS was significantly higher in those treated with high-dose IMN RT than in those treated with low-dose IMN RT (69.3% vs. 33.3%, p = 0.019). CONCLUSIONS: IMN RT without IMN dissection resulted in favorable outcomes in cIMN+ breast cancer. For patients with a large IMN, a higher IMN radiation dose might be needed for disease control.