Internal mammary node irradiation improves 8-year survival in breast cancer patients: results from a retrospective cohort study in real-world setting

Abstract

Regional nodal irradiation (RNI) improves disease outcome in breast cancer patients, but the contribution of internal mammary node irradiation (IMNI) in the context of modern systemic treatment is still controversial. The aim of our study is to evaluate the effect of IMNI in patients with modern systemic treatment in real-world setting. We retrospectively analyzed patients with primary breast cancer treated with surgery followed by adjuvant chemotherapy and adjuvant chestwall/breast irradiation and RNI from 5/2007-12/2010. RNI was delivered to the ipsilateral supraclavicular region and infraclavicular region + / - IMNs. We separated two groups based on the presence and the absence of IMNI. The primary end point was disease-free survival (DFS). DFS and overall survival (OS) were evaluated with Kaplan-Meier method. Differences between two groups were compared with the log-rank test (p < 0.05 considered significant). We used two methods to account for potential confounders: propensity score matching (PSM) and Cox regression analysis. We analyzed 872 patients who received RNI with IMNI (n = 390) or without IMNI (n = 482). Median radiation dose was 50Gy. Median follow-up was 98months. IMNI improved 8-year DFS rates versus no IMNI: 75.9% and 64.9% (p < 0.001). After PSM, baseline characteristics were well balanced between the two groups. IMNI significantly improved DFS (p < 0.001) in patients after PSM. IMNI was an independent prognostic factor for DFS. In this study, we found that IMNI improved DFS and OS in breast cancer patients in the context of modern systemic treatment. These data continue to support that IMNI is a key component of RNI.