Radiotherapy Plays an Important Role in Improving the Survival Outcome in Patients with T1-2N1M0 Breast Cancer – A Joint Analysis of 4209 Real-world Cases from Two Institutions.

Abstract

To compare the survival outcomes between breast-conserving surgery (BCS) and mastectomy, and investigate the role of radiotherapy (RT) in patients with T1-2N1M0 breast cancer in a real-world setting. There were 4209 women with T1-2N1M0 breast cancer treated in two institutions between 1999 and 2014 were retrospectively reviewed. All had received lumpectomy or mastectomy and axillary lymph node dissection without neoadjuvant chemotherapy. 3858 patients underwent modified radical mastectomy (MRM), 832 (21.6%) of them received postoperative RT (MRM + RT). 351 patients received BCS, all of them received postoperative RT (BCS + RT). Overall survival (OS) and disease-free survival (DFS) rates were calculated by using the Kaplan-Meier method and compared by log-rank test. The association of survival outcome with choice of different surgical modalities (BCS vs. MRM) and the role of RT were evaluated using multivariable proportional hazards regression and further confirmed with propensity score-matching (PSM) methods. At a median follow-up of 70 months (range, 6-226 months), the 5-year OS rates of the BCS and MRM group were 96.0% and 92.7% (p=0.005), and the corresponding 5-year DFS rates were 92.8% vs 84.0% (p<0.001). Multivariate analysis revealed that T stage, the number of positive axillary lymph node, histological grade, molecular subtype, Her2 status & target therapy, and RT were all independent prognostic factors for OS (p<0.05) and DFS (p<0.05). However, the type of breast surgery was not independently associated with either OS (p=0.788) or DFS (p=0.088). Between 326 pairs of patients (BCS + RT vs. MRM without RT) matched by PSM, BCS + RT group enjoyed significantly higher 5-year OS (96.0% vs. 94.0%, p=0.045) and DFS (92.8% vs. 87.0%, p=0.018). In further analysis of 1116 pairs of patients (BCS or MRM + RT vs. MRM without RT) matched by PSM, BCS or MRM + RT group had significantly higher 5-year OS (94.3% vs. 87.3%, p<0.001) and DFS (86.4% vs. 78.0%, p<0.001) than MRM without RT group. Based on this real-world-case analysis, we find that breast conserving surgery had superior survival outcomes to mastectomy in patients with T1-2N1M0 breast cancer, in which postoperative radiotherapy plays an important role. These findings need further validation.