Prognostic value of primary tumor surgery in de novo stage IV breast cancer patients with different metastatic burdens: a propensity score-matched and population-based study

Background: Whether primary tumor surgery should be performed in breast cancer patients with metastatic disease at diagnosis has been debated for decades. This study aims to evaluate the value of primary tumor surgery with respect to the mortality of patients with de novo stage IV breast cancer and to define the heterogeneity of this population. Methods: De novo stage IV patients from the Surveillance, Epidemiology and End Results database (SEER) from 2010 to 2015 were included in our study. Propensity score matching (PSM) and inverse probability of treatment weighting (IPTW) were used to achieve balanced baseline characteristics. The effect of surgery was assessed by Kaplan-Meier curves and Cox regression models. Results: Of the 11,684 patients eligible for analysis, 3,730 (31.92%) received primary tumor surgery. Multivariate Cox regression in the PSM cohort revealed that surgery was associated with better outcomes than those in the nonsurgery group in terms of overall survival (OS) [hazard ratio (HR): 0.51; 95% Cl: 0.48-0.55; P<0.001] and breast cancer-specific survival (BCSS) (HR: 0.51; 95% CI: 0.47-0.55; P<0.001). IPTW analysis yielded similar results. In a subgroup analysis, surgery was associated with better survival in all subtypes with low metastatic burdens (<= 2 metastatic sites), but triple-negative breast cancer with a high metastatic burden (>2 metastatic sites) did not benefit from surgery (HR: 0.78; 95% Cl: 0.31-1.97, P=0.596 and 0.78, 95% CI: 0.31-1.97, P=0.596 for OS and BCSS, respectively). Conclusions: Primary tumor surgery significantly prolonged the survival of patients with de novo stage IV breast cancer. However, triple-negative breast cancer patients with more than two metastatic sites may not benefit from surgery.