Abstract
BACKGROUND: To define the role of post-mastectomy radiotherapy (PMRT) in triple-negative breast cancer (TNBC), employing lymph node ratio (LNR, ratio of positive over excised lymph nodes) to offer personalized treatment strategies for this aggressively behaving cancer type. METHODS: The study included a total of 6474 women diagnosed with T1-4 N1-3 M0 TNBC from 2010 to 2017 using the SEER database, all of whom underwent mastectomy. Breast cancer-specific survival (BCSS) was defined as the time from diagnosis until death attributable to the breast cancer. Overall survival (OS) was defined as the time from diagnosis until death from any cause. A 1:1 propensity score matching (PSM) method was utilized to balance the baseline characteristics between the PMRT and non-PMRT groups. Kaplan-Meier analysis, together with the log-rank test, was applied to estimate survival outcomes. RESULTS: After PSM, the PMRT group displayed better OS (HR(OS) = 0.898, 95% CI = 0.819-0.984, p = 0.021). Subgroup analyses indicated that PMRT improved BCSS outcomes in the high-LNR group (HR(BCSS) = 0.762, 95% CI = 0.636-0.913; p = 0.003) rather than low- (HR(BCSS) = 1.125, 95% CI = 0.938-1.348; p = 0.203) or intermediate-LNR groups (HR(BCSS) = 0.925, 95% CI = 0.778-1.099; p = 0.374). Compared with the non-PMRT group, patients receiving PMRT had better OS in the intermediate-LNR (HR(OS) = 0.834, 95% CI = 0.715-0.972, p = 0.021) and high-LNR groups (HR(OS) = 0.757, 95% CI = 0.643-0.893, p = 0.001), whereas the difference was not significant in the low-LNR group (HR(OS) = 1.044, 95% CI = 0.889-1.226, p = 0.599). CONCLUSION: PMRT substantially improves the survival outcomes for individuals who fall into the intermediate to high-risk groups as determined by LNR, an essential prognostic factor. This helps in developing personalized PMRT treatment strategies for TNBC patients, thereby enabling precision medicine approaches.