Outcome of post-mastectomy radiotherapy after primary systemic treatment in patients with different clinical tumor and nodal stages of breast cancer: a cohort study.

To evaluate the effect of post-mastectomy radiation therapy (PMRT) stratified by clinical tumor (T) or nodal (N) staging and determine predictors of overall survival (OS), locoregional recurrence (LRR), distant metastasis, and disease-free survival (DFS) in patients with breast cancer who received neoadjuvant chemotherapy (NACT) and total mastectomy (TM), we enrolled patients who received a diagnosis of breast invasive ductal carcinoma who received NACT followed by TM. Cox regression analysis was employed to calculate hazard ratios (HRs) and confidence intervals (CIs). Univariate and multivariate Cox regression analyses indicated that non-PMRT, Charlson comorbidity index ≥ 2, advanced clinical T or N stage, pathologic partial response, pathologic stationary disease, or pathologic progression disease were poor prognostic factors for OS. Well-differentiated tumor grade, pathologic complete response, and positive hormone receptors were better independent prognostic factors for OS. Adjusted HRs derived from PMRT for breast cancer after NACT and TM were 0.69 (0.53-0.89) and 0.74 (0.59-0.93) in clinical T3 and T4, respectively. aHRs derived from PMRT for breast cancer after NACT and TM were 0.67 (0.45-0.99), 0.75 (0.62-0.92), and 0.77 (0.60-0.98) in clinical N0, N1, N2-3, respectively. The aHRs (95% CI) of the PMRT group to the non-PMRT group for LRR-free survival and DFS were improved significantly. Our study indicated that PMRT significantly improved OS in clinical T3N0-T4N3 and for LRR-free survival and DFS in clinical T2N0-T4N3 from those of non-PMRT patients regardless of pathologic response and other predictors.