Is it beneficial for patients with early breast cancer after mastectomy to receive internal mammary node irradiation? A propensity-matched analysis of a retrospective cohort

Background: The association between internal mammary lymph node irradiation (IMNI) and survival in patients with early-stage breast cancer is currently controversial. Objective: We examined the effect of IMNI in patients treated with mastectomy and systemic treatment in China. Methods: We analyzed women with early-stage breast cancer who underwent mastectomy followed by adjuvant chest wall and regional lymph node irradiation (RNI) from the Breast Cancer Information Management System (BCIMS). We analyzed women with early-stage breast cancer who underwent mastectomy followed by adjuvant chest wall and regional lymph node irradiation (RNI) from the BCIMS. Patients were categorized into two groups: those who received IMNI and those who received no IMNI. Disease-free survival (DFS) was the primary endpoint. Cox proportional hazards models and propensity score-matching methods were used to calculate hazard ratios (HRs) with 95% confidence intervals (CIs) and to minimize bias. Results: In accordance with the study inclusion and exclusion criteria, a total of 1,015 patients were included, of whom 189 received adjuvant irradiation with IMNI and 826 received no IMNI. After propensity score matching, baseline characteristics were well-balanced between the two groups. During a median follow-up of 8.9 years, patients treated with IMNIfailed to achieve a better DFS (HR, 0.36; 95% CI, 0.13–0.99; P = 0.04) compared with those treated without IMNI after adjusting for confounders. Subtype analysis further showed that there was an elevated association between IMNI and decreased DFS. Conclusion: In China, our findings suggest that the inclusion of IMNs in the RNI protocol aftermastectomy has no survival benefit over twenty decades ago and needs to be carefully considered. Randomized studies are required to further confirm the influence of IMNI on prognosis.