Postmastectomy radiation therapy can improve survival for breast cancer patients with 1–3 positive axillary lymph nodes: a retrospective cohort study using the SEER database

BACKGROUND: Postmastectomy radiation (PMRT) is an important adjuvant treatment for high-risk breast cancer. However, evidence concerning its efficacy in promoting survival of patients with 1–3 positive axillary lymph nodes remains insufficient. METHODS: We identified 57,793 patients, diagnosed from 2010–2015, from the Surveillance, Epidemiology, and End Results database, including 15,126 cases treated with beam radiation and 42,667 cases with none/unknown radiation. A Kaplan–Meier curve was utilized to compare survival of the two groups. We used univariate and multivariate Cox proportional hazard models to identify independent prognostic factors presented as hazard ratios (HRs) and 95% confidence intervals (CIs). For subgroup analysis, patients were stratified according to lymph node status, tumor size, and molecular subtypes. RESULTS: The PMRT group showed more aggressive clinicopathological features, including higher grades (P<0.001), larger tumor sizes (P<0.001), more lymph nodes (P<0.001), younger ages (P<0.001), more ER-negative cases (P<0.001), more PR-negative cases (P<0.001), and more HER2 overexpression (P<0.001). In addition, the PMRT group received more radical surgeries (P<0.001) and more chemotherapy (P<0.001). In the multivariate Cox proportional hazard regression analysis, the PMRT group exhibited improved survival in terms of breast cancer specific survival (BCSS) (HR, 0.74; 95% CI, 0.68–0.81; P<0.001) and overall survival (OS) (HR, 0.72; 95% CI, 0.67–0.78; P<0.001). After stratification according to positive axillary lymph nodes, the PMRT group showed improved BCSS and OS in the LN 1 to 3 subgroup (HR, 0.74; 95% CI, 0.64–0.85; P<0.001 and HR, 0.68; 95% CI, 0.60–0.78; P<0.001, respectively). For patients with 1–3 positive axillary lymph nodes and T1–2 tumors, the PMRT group still showed improved BCSS and OS (HR, 0.823; 95% CI, 0.69–0.99; P=0.04 and HR, 0.75; 95% CI, 0.64–0.88; P<0.001, respectively). In the subgroup analysis, PMRT remained a significant favorable prognostic factor in T2 and HER2−/HR+ subtype (P<0.05). CONCLUSIONS: This study suggests that PMRT can confer a survival benefit to breast cancer patients with 1–3 positive axillary lymph nodes, even with modern treatment options. Furthermore, for patients with 1–3 positive axillary lymph nodes and T1–2 tumors, PMRT can still provide survival benefits.