[The role of postmastectomy radiotherapy in clinical T1-3N1M0 breast cancer patients with pathological negative lymph nodes after neoadjuvant chemotherapy and mastectomy].

Objective: To analyze the outcomes of clinical T1-3N1M0 breast cancer patients with pathological negative axillary lymph nodes (ypN0) after neoadjuvant chemotherapy (NAC) and mastectomy, and investigate the role of postmastectomy radiotherapy (PMRT).
Methods: A total of 185 patients with clinical T1-3N1M0 breast cancer treated between 1999 and 2013 were retrospectively reviewed. All patients were treated with NAC and mastectomy, and achieved ypN0. Of them, 89 patients received additional PMRT and 96 patients did not. 101 patients had clinical stage Ⅱ disease. 84 patients had clinical stage Ⅲ disease. The rates of locoregional recurrence (LRR), distant metastasis (DM), disease-free survival (DFS), and overall survival (OS) were calculated using the Kaplan-Meier method, and differences were compared using the log-rank test. Univariate analysis was used to interpret the impact of clinical features and treatment on patients' outcome.
Results: The 5-year rates of LRR, DM, DFS, and OS for all patients were 4.5%, 10.4%, 86.6%, and 97.1%, respectively. For patients with and without PMRT, the 5-year LRR rates were 1.1% and 7.5% (P=0.071), the 5-year DM rates were 5.1% and 15.0% (P=0.023), the 5-year DFS rates were 95.0% and 79.0% (P=0.008), and the 5-year OS rates were 100.0% and 94.5% (P=0.089) respectively. In univariate analysis, lymph-vascular space invasion (LVSI) was poor prognostic factor of LRR (P=0.001), < 40 years old and lack of PMRT was a poor prognostic factor for DM (P<0.05), lack of PMRT was a poor prognostic factor for DFS (P=0.008), primary lesion residual and mild-moderate pathological response to NAC were poor prognostic factors for OS (P<0.05). In the subgroup of Stage Ⅲ disease, for patients with and without PMRT, the 5-year LRR rates were 1.9% and 14.4% (P=0.041), the 5-year DFS rates were 91.9% and 67.4% (P=0.022), respectively. In the subgroup of Stage Ⅱ disease, for patients with and without PMRT, the 5-year DM rates were 0 and 11.5% (P=0.044), the 5-year DFS rates were 100.0% and 84.9% (P=0.023), respectively. Conclusions: The LRR rate of clinical T1-3N1M0 breast cancer patients who achieved ypN0 after NAC and mastectomy was low. PMRT decreased the DM rate and increased DFS rate in all patients, and significantly decreased the LRR rate in Stage Ⅲ disease. PMRT should be considered for patients with Stage Ⅲ disease, and further research is warranted to investigate the benefit of PMRT for Stage Ⅱ disease.