The Role of Post-Mastectomy Radiotherapy in T1-2N1 Breast Cancer Patients: Propensity Score Matched Analysis

SIMPLE SUMMARY: With the development of modern systemic therapy, the role and indications of PMRT need to be further investigated in early-stage N1 breast cancer patients who have received upfront mastectomy, as recent guidelines still do not reach a consensus. Our study aimed to identify risk factors that may worsen treatment outcomes, and found that three lymph node metastases were prognostic for loco-regional control (LRC), disease-free survival (DFS), and lympho-vascular invasion (LVI) for overall survival (OS). However, the benefit of PMRT was not evident even in patients with these risk factors, and the results were similar after propensity score matching. Moreover, the incidence of arm lymphedema was significantly higher after PMRT. Therefore, we cautiously suggest omitting PMRT in T1-2N1 breast cancer patients, given the similar oncologic outcomes and increased risk of RT-related toxicity after PMRT. ABSTRACT: This study aimed to evaluate the role of post-mastectomy radiotherapy (PMRT) in T1-2N1 breast cancer. Between 2006 and 2014, a total of 504 patients with T1-2N1 breast cancer were analyzed. PMRT was administered to 71 patients, and 1:2 propensity score matching (PSM) was performed between the PMRT and non-PMRT groups. Loco-regional control (LRC), disease-free survival (DFS), and overall survival (OS) rates were compared according to PMRT status. Thirteen and one loco-regional recurrences were observed in the PMRT and non-PMRT groups, respectively. Before PSM, the 8-year LRC, DFS, and OS rates in the non-PMRT and PMRT groups were 98.5% and 96.5% (p = 0.426), 89.7% and 91.2% (p = 0.700), and 91.5% and 92.1% (p = 0.679), respectively. Corresponding rates were 95.6% and 96.5% (p = 0.365), 84.1% and 91.2% (p = 0.185), and 88.4% and 92.1% (p = 0.276), respectively, after PSM. Multivariate analysis showed that three lymph node metastases were prognostic for LRC and DFS rates and LVI for OS rate. Arm lymphedema developed in 32.4% of patients who received PMRT, which was significantly higher than the non-PMRT group (p < 0.001). Contributions of PMRT for improvement of treatments outcomes in T1-2N1 breast cancer patients were not evident, while the incidence of arm lymphedema significantly increased after PMRT. Further prospective trials are required to re-evaluate the role of PMRT.