Effect of postmastectomy radiotherapy on T1-2N1M0 triple-negative breast cancer

Background: The effect of postmastectomy radiotherapy (PMRT) on T1-2N1M0 triple-negative breast cancers (TNBC) remains unclear. The population-based study aimed to investigate the survival outcomes of T1-2N1M0 TNBC patients who underwent PMRT or not. Methods: We selected 1743 patients with T1-2N1M0 TNBC who underwent mastectomy between 2010 and 2015 through the Surveillance, Epidemiology and End Results (SEER) database. After propensity score matching (PSM) , the PMRT and no-PMRT groups consisted of 586 matched patients, respectively.The Kaplan-Meier method was applied to calculate breast cancer-specific survival (BCSS) and cox proportional hazard model were used to determine the prognostic factors of T1-2N1M0 TNBC.Results: The 5-year BCSS for the PMRT group and no-PMRT group was 79.1% and 74.7%, respectively. TNBC patients with stage T1-2N1M0 receiving PMRT did not show better BCSS than those did not (HR =0.800, 95% CI =0.605-1.056, P =0.115). Subgroup analysis showed that in patients with three nodes positive, radiotherapy could significantly improve BCSS(HR=0.396, 95% CI = 0.175-0.900, P = 0.027), but it brought no significant advantage in BCSS in patients with one or two nodes positive(HR =1.061, 95% CI =0.725-1.552, P =0.761; HR =0.657, 95% CI =0.405-1.065, P =0.088).In addition, PMRT improves the BCSS in TNBC patients with T2 tumor concomitant with three positive lymph nodes(HR =0.343, 95% CI =0.132-0.890, P =0.028).Conclusion: TNBC patients with T2 tumor concomitant with three positive lymph node can benefit from PMRT.