General characteristics of the study population and tumor
A total of 1197 patients were enrolled in the study through the SEER database. Participants were allocated into two groups based on the surgical method. They were subjected to: the BCS+RT group (439, 36.68%) and the mastectomy group (758, 63.32%). Patients in the BCS+RT group showed smaller tumors (P<0.001), fewer lymph node metastases (P<0.001), and a higher PR negative rate compared to patients in the mastectomy group (P<0.05). Moreover, the odds of chemotherapy and radiotherapy administration to patients in the BCS+RT group was significantly high compared to those in the mastectomy group (P<0.001).Considering the different between case and control groups.We used PSM to construct a matched sample consisting of 321 pairs of BCS+RT and mastectomy subjects. There were no difference between the variables of the two groups after PSM.Table 1 shows the demographic and clinicopathological characteristics of the two groups.
Comparison of BCSS and OS Between BCS+RT and mastectomy groups
To determine the effectiveness of the two surgical procedures, OS and BCSS in patients who had been subjected to BCS + RT and mastectomy were compared. Before PSM,the median follow-up time was 56 months. Among patients in the BCS + RT group, Kaplan-Meier analysis showed a significantly high OS and BCSS when compared to those in the mastectomy group (all log-rank P<0.05,Figure 1). The 5-year OS for patients who had been subjected to BCS+RT and mastectomy were 85.1% and 67.7%, while the 10-year OS for patients in the two groups were 77.1% and 55.5%, respectively. The 5-year BCSS for patients who had been subjected to BCS+RT and mastectomy were 90.2% and 78.7%, while the 10-year BCSS were 86.5% and 76.3%, respectively.After PSM with a 6 months landmark, Patients in the BCS + RT group showed a significantly high OS outcomes compared to patients in the mastectomy group(log-rank P=0.042, Figure 2A),while patients in the two subjects had similar BCSS(log-rank P =0.181, Figure 2B). The 5-year OS for the group with BCS + RT was 84.6% and was 78.7% in the mastectomy group,while the 10-year OS for patients in the two groups were 75.1% and 66.7%.Similar 5-year and 10-year BCSS were found for the two groups (5-year:BCS + RT,89.6% vs. mastectomy, 85.0%;10-year:BCS + RT,85.0% vs. mastectomy, 83.6%).
Prognostic factors associated with OS and BCSS
Before PSM, multivariate cox regression analysis showed that larger tumors and more lymph node metastases were associated with poor BCSS and OS. Chemotherapy (HR = 1.968, 95% CI=1.538-2.517, P<0.001) and BCS + RT (HR = 0.697, 95% CI = 0.527-0.922, P = 0.012) were only associated with improved OS, but not BCSS(Table 2).After PSM, the results of multivariate cox regression analysis, with a 6-month landmark showed that factors associated with OS and BCSS were same as the fators before PSM.Patients who had larger tumors and more lymph node metastases showed poor BCSS and OS.Surgical type and chemotherapy are independent OS prognostic factors.Patients in the BCS + RT group showed a significantly high OS outcomes compared to patients in the mastectomy group (HR = 0.684,95% CI = 0.479-0.977, P=0.037).Patients who were not administered with chemotherapy showed low OS compared to those who had received chemotherapy (HR =2.253, 95% CI=1.457-3.485, P<0.001)(Table 3).
Stratified analysis of OS and BCSS
A stratified analysis of all patients after PSM was performed to determine the possible factors affecting the overall survival time for patients who had been subjected to the two types of surgical procedures. Stratified analysis was based on age, diagnostic year, race, marital status, histological grade, tumor size (T stage), lymph node status, ER, PR, surgical methods and postoperative chemotherapy (Table 4). After adjusting for the important prognostic variables in the univariate analysis, the multivariate analysis showed significantly high OS when BCS+RT was given to patients aged between 20-49 years,the white race group,patients with grade III+IV, patients with T2, patients with ER positive and those who received chemotherapy(See Supplementary Figure 1, Additional File 1).No factors were associated with the BCSS of patients who received BCS+RT.