IntroductionThe role of radiotherapy (RT) in de novo metastatic breast cancer (dnMBC) patients undergoing surgery remains controversial due to limited evidence. This study aimed to evaluate the impact of postoperative radiotherapy on survival outcomes in this population.Materials and methodsWe retrospectively analyzed 102 dnMBC patients who underwent surgery at a provincial cancer hospital. Patients were grouped based on whether they received postoperative RT. Baseline characteristics were compared using the chi-square test. Kaplan-Meier analysis and Cox proportional hazards models were used to assess the prognostic impact of postoperative radiotherapy on local recurrence-free survival (LRFS), progression-free survival (PFS), and overall survival (OS).ResultsKM survival analysis showed that postoperative RT significantly improved LRFS (HR = 0.3634, 95%CI 0.1552-0.8508,  = .0197) and PFS (HR = 0.4903, 95%CI 0.3061-0.7855,  = .003) but had no significant effect on OS (HR = 0.7337, 95%CI 0.3514-1.508,  = .5395). Multivariate analysis identified postoperative RT as an independent protective factor for LRFS (HR = 0.265, 95%CI 0.088-0.795,  = .018) and PFS (HR = 0.525, 95%CI 0.313-0.882,  = .015). Subgroup analysis showed that for LRFS, RT had no significant interaction with different subgroup classification variables (all interaction  > .05). However, RT had a significant interaction with N stage for PFS ( = .016), specifically in N1-3 patients (HR = 0.384, 95% CI 0.221-0.668).ConclusionRT may improve disease control in selected dnMBC patients undergoing surgery, particularly those with lymph node metastasis. However, these findings still require further validation in larger, multicenter cohorts.