Radiotherapy plays an important role in improving the survival outcome in patients with T1-2N1M0 breast cancer - a joint analysis of 4262 real world cases from two institutions.

BACKGROUND: To compare the survival outcomes between breast-conserving surgery (BCS) and modified radical mastectomy (MRM), and to investigate the role of radiotherapy (RT) in patients with pT1-2N1M0 breast cancer. METHODS: A total of 4262 women with T1-2N1M0 breast cancer treated at two institutions were retrospectively reviewed. A total of 3858 patients underwent MRM, and 832 (21.6%) of them received postoperative RT (MRM + RT). A total of 404 patients received BCS plus postoperative RT (BCS + RT). All patients received axillary lymph node dissection, while 3.8% of them had upfront sentinel node biopsy. The association of survival outcomes with different surgical modalities (BCS vs. MRM) and the role of RT were evaluated using multivariable proportional hazards regression and confirmed by the propensity score-matching (PSM) method. RESULTS: At a median follow-up of 71 months (range of 6-230 months), the 5-year overall survival (OS) rates of the BCS and MRM groups were 96.5 and 92.7%, respectively (P = .001), and the corresponding 5-year disease-free-survival (DFS) and locoregional recurrence (LRR) rates were 92.9 and 84.0%, and 2.0 and 7.0% (P = .001), respectively (P < .001). Multivariate analysis revealed that RT was an independent prognostic factor for improved OS (P = .001) and DFS (P = .009), and decreased LRR (P < .001). However, surgery procedure was not independently associated with either OS (P = .495), DFS (P = .204), or LRR (P = .996), which was confirmed by PSM analysis. CONCLUSION: Postoperative radiotherapy rather than the surgery procedures was associated with superior survival outcomes in patients with T1-2N1M0 breast cancer.