DBCG-IMN: A Population-Based Cohort Study on the Effect of Internal Mammary Node Irradiation in Early Node-Positive Breast Cancer

J Clin Oncol. 2016 Feb 1;34(4):314-20. doi: 10.1200/JCO.2015.63.6456. Epub 2015 Nov 23.


Purpose: It is unknown whether irradiation of the internal mammary lymph nodes improves survival in patients with early-stage breast cancer. A possible survival benefit might be offset by radiation-induced heart disease. We assessed the effect of internal mammary node irradiation (IMNI) in patients with early-stage node-positive breast cancer.

Patients and methods: In this nationwide, prospective population-based cohort study, we included patients who underwent operation for unilateral early-stage node-positive breast cancer. Patients with right-sided disease were allocated to IMNI, whereas patients with left-sided disease were allocated to no IMNI because of the risk of radiation-induced heart disease. The primary end point was overall survival. Secondary end points were breast cancer mortality and distant recurrence. Analyses were by intention to treat.

Results: A total of 3,089 patients were included. Of these, 1,492 patients were allocated to IMNI, whereas 1,597 patients were allocated to no IMNI. With a median of 8.9 years of follow-up time, the 8-year overall survival rates were 75.9% with IMNI versus 72.2% without IMNI. The adjusted hazard ratio (HR) for death was 0.82 (95% CI, 0.72 to 0.94; P = .005). Breast cancer mortality was 20.9% with IMNI versus 23.4% without IMNI (adjusted HR, 0.85; 95% CI, 0.73 to 0.98; P = .03). The risk of distant recurrence at 8 years was 27.4% with IMNI versus 29.7% without IMNI (adjusted HR, 0.89; 95% CI, 0.78 to 1.01; P = .07). The effect of IMNI was more pronounced in patients at high risk of internal mammary node metastasis. Equal numbers in each group died of ischemic heart disease.

Conclusion: In this naturally allocated, population-based cohort study, IMNI increased overall survival in patients with early-stage node-positive breast cancer.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adult
  • Breast Neoplasms / mortality
  • Breast Neoplasms / pathology
  • Breast Neoplasms / radiotherapy*
  • Breast Neoplasms / surgery
  • Cohort Studies
  • Denmark / epidemiology
  • Female
  • Humans
  • Lymph Nodes / pathology
  • Lymph Nodes / radiation effects*
  • Lymphatic Metastasis
  • Middle Aged
  • Prospective Studies
  • Radiotherapy, Adjuvant