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OBJECTIVE The aim was to evaluate the impact of local surgery performed during the year following metastatic breast cancer (MBC) diagnosis on patients' outcomes from a large real-life cohort. SUMMARY BACKGROUND DATA Locoregional treatment for patients with MBC at the time of diagnosis remains debated. METHODS Women with newly diagnosed, de novo stage IV MBC and who started MBC treatment between January 2008 and December 2014 in one of the 18 French Comprehensive Cancer Centers were included (NCT03275311). The impact of local surgery performed during the first year on overall survival (OS) and progression-free survival (PFS) was evaluated by the Cox proportional hazards model in a 12 month-landmark analysis. RESULTS Out of 16,703 patients in the ESME database, 1,977 had stage IV MBC at diagnosis, were alive and progression-free at 12 months and eligible for this study. Among them, 530 (26.8%) had received primary breast cancer surgery within 12 months. A greater proportion of patients who received surgery had less than 3 metastatic sites than the no-surgery group (90.8% vs 78.2%, p < 0.0001). Surgery within 12 months was associated with treatment with chemotherapy, HER2-targeted therapy (89.1% vs 69.6%, p < 0.0001) and locoregional radiotherapy (81.7% vs 32.5%, p < 0.0001). Multivariable analyses showed that surgery performed within 12 months was associated with longer OS and PFS (adjusted HR [95%CI] = 0.75 [0.61 - 0.92] and 0.72 [0.63 - 0.83], respectively), which were also affected by pattern and number of metastatic sites, histological subtype and age. CONCLUSIONS In the large ESME cohort, surgery within one year after de novo MBC diagnosis was associated with a significantly better OS and PFS.