Prognostic factors and outcomes associated with postmastectomy radiation therapy following neoadjuvant chemotherapy and mastectomy for breast cancer: A retrospective cohort study.

The indications for postmastectomy radiation therapy (PMRT) after neoadjuvant chemotherapy (NAC) remain controversial. We aimed to identify prognostic factors and investigate subgroups in which PMRT could improve treatment outcomes. This study included 178 patients with clinical stage II-III breast cancer who underwent mastectomy after NAC between May 2006 and December 2022. PMRT was administered to 149 (83.7%) patients. The median follow-up period was 64 months. The response to NAC, molecular subtype, and pathologic stage were independent predictors of treatment outcomes. The human epidermal growth factor receptor 2 (HER2)-positive and triple-negative (TN) molecular subtypes were associated with significantly higher pathologic complete response (ypCR) rates than the luminal HER2-negative subtype. Twenty-six patients (14.6%) achieved ypCR after NAC, and the overall response rate was 77.5%. Non-responders to NAC showed significantly worse 5-year locoregional control (LRC, P = .01), progression-free survival (PFS, P< .01), and overall survival (OS, P< .01). Despite the relatively high likelihood of achieving ypCR, the TN subtype was significantly associated with worse 5-year LRC (P< .01), PFS (P = .02), and OS (P = .02) compared with the luminal HER2-negative and HER2-positive subtypes. With regard to the pathologic lymph nodal stage, PMRT did not confer significant benefits in terms of LRC (P = .20), PFS (P = .30), or OS (P = .70) in the pathologically node-negative (ypN0) subgroup, but its use led to significant improvements in LRC (P< .01), PFS (P< .01), and OS (P = .02) in the ypN1-3 subgroup. nonresponse to NAC and TN molecular subtype were poor prognostic factors for survival. PMRT was associated with improved survival outcomes in patients with residual lymph nodes following NAC and mastectomy.