Internal Mammary Node Irradiation (IMNI) Improves Survival Outcome for Patients With Clinical Stage II-III Breast Cancer After Preoperative Systemic Therapy

Abstract

The indication for internal mammary node irradiation (IMNI) after preoperative systemic therapy in breast cancer remains vague. This study was designed to evaluate the effect of IMNI in patients with clinical stage II-III breast cancer after preoperative systemic therapy and surgery. Between August 2005 and December 2013, 497 patients with clinical stage II-III breast cancer underwent anthracycline- or taxane-based preoperative systemic therapy, surgery, and postoperative radiation therapy. A median dose of 50Gy (range, 46-60Gy) in 25 fractions was delivered to the chest wall or breast with IMNI (n=236) or without IMNI (n=261). Disease-free survival (DFS) and overall survival (OS) rates with or without IMNI were evaluated using the Kaplan-Meier method and compared with the log-rank test. Propensity score matching was performed to adjust for the unbalanced characteristics between the 2 groups. Prognostic factors associated with survival were evaluated by univariate and multivariate analysis. The median follow-up time was 64months. Patients with IMNI presented with more advanced clinical T stage, pathologic N stage, positive lymph-vascular invasion, and medically or centrally located disease (P<.05). The 5-year DFS and OS rates were 73.7% and 86.3% in the IMNI group and 71.5% and 86.7% in the non-IMNI group, respectively (P>.05). Multivariate analysis demonstrated that IMNI was an independent prognostic factor for DFS (P=.018) and resulted in a borderline improvement in OS (P=.067). After propensity score matching, characteristics were well balanced. The 5-year DFS rates of IMNI and non-IMNI group were 76.8% and 63.4%, respectively (P=.030), and the 5-year OS rates were 88.9% and 84.1%, respectively (P=.083). IMNI was independently prognostic for DFS (P=.014) and OS (P=.047) in matched patients. IMNI improves survival outcomes in patients with clinical stage II-III breast cancer after preoperative systemic therapy. Further prospective studies are warranted to identify the role of IMNI in the preoperative systemic therapy setting.