Comparison of breast-conserving surgery and mastectomy in early breast cancer using observational data revisited: a propensity score-matched analysis

Recent observational studies showed that breast-conserving surgery (BCS) resulted in superior survival compared to mastectomy in breast cancer patients. This study compared the clinical outcomes of BCS and mastectomy using propensity score (PS) matching analysis, which had advantages over conventional methods in reducing bias. Nonmetastatic breast cancer patients who underwent BCS and mastectomy were matched 1:1 based on their PS. We used the Kaplan-Meier method and Cox-regression model to estimate the treatment effects. A total of 2,866 patients with a median follow-up time of 67 months were included in the original study population. Although the mastectomy cohort (N=1,219) had more advanced disease compared to the BCS cohort (N=1,647), LRFS was similar between the two groups (93.8% vs. 92.4%, P>0.05). BCS (vs. mastectomy) was associated with improved DFS (73.8% vs. 58.7%, P<0.01) and CSS (91% vs. 78.2%, P<0.01) in the original population. In the PS-matched population (N=1,668), clinicopathological features were equally distributed between the two cohorts. BCS (vs. mastectomy) was not associated with improved DFS (70.7% vs. 66.9%, P>0.05) or CSS (87.5% vs. 84.9%, P>0.05). We found that PS methods reduce bias when estimating treatment effects using observational data. BCS and mastectomy show equivalent outcomes in nonmetastatic breast cancer patients.