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We aimed to investigate the prognostic value of postpathological characters in nonmetastatic breast cancer (NMBC) patients who received preoperative radiotherapy (PRT) followed by mastectomy (MAST).We conducted retrospective analyses using the data collected from the Surveillance, Epidemiology, and End Results program of the National Cancer Institute. Univariate and multivariate analyses were performed to identify prognostic factors. Disease-specific survival was calculated by the Kaplan–Meier curve and validated by log rank test. The discriminations of independent risk factors and staging systems were compared by the area under receiver operating characteristic curves (AUC) and validated by Harrell concordance index (bootstrapping algorithm). Akaike information criterion (AIC) was applied to compare the difference of model.One thousand three hundred fifty NMBC patients who had received PRT followed by MAST from 1988 to 2013 were included in the study. We found the metastatic lymph node ratio (mLNR) staging was a superior indicator than pN staging. Thus, we proposed a T-lymph node ratio (T-NR) staging system with simplified-T categories (T0–3 and T4) and the mLNR staging. The novel T-NR staging system provided larger AUC (P = .024, .008, respectively) and the smaller AIC (P < .001) value than American Joint Committee on Cancer staging system.The novel T-NR staging system performed more accurate survival prediction and better model fitness for NMBC patients who receive PRT followed by MAST, it may provide a wide applicability in clinical decision-making.