Survival Impact of Locoregional Treatment of the Primary Tumor in De Novo Metastatic Breast Cancers in a Large Multicentric Cohort Study: A Propensity Score-Matched Analysis

{Improvement in overall survival (OS) by locoregional treatment (LRT) of the primary tumor in de novo metastatic breast cancer (MBC) patients remains controversial. The aim of our study was to evaluate the impact of LRT on OS in a large retrospective cohort of de novo MBC patients, with regard to immunohistochemical characteristics and pattern of metastatic dissemination. We conducted a multicentric retrospective study of patients diagnosed with de novo MBC selected from the French Epidemiological Strategy and Medical Economics MBC database (NCT03275311) between 2008 and 2014. Overall, 4276 women were included in the study. LRT comprised either radiotherapy, surgery, or both. LRT was used in 40% of patients. Compared with no LRT, patients who received LRT were younger (p < 0.0001) and were more likely to have only one metastatic site (p < 0.0001) or bone-only metastases (p < 0.0001). LRT was associated with a significantly better OS based on landmark multivariate analysis at 1-year (hazard ratio 0.65, 95% confidence interval 0.55-0.76, p < 0.001). Similar results were observed in all sensitivity analyses, including propensity score matching. In subgroup analysis, LRT was associated with better OS in patients with hormone receptor-positive/human epidermal growth factor receptor 2 (HER2)-negative (61.6 vs. 45.9 months, p < 0.001) and HER2-positive tumors (77.2 vs. 52.6 months