Value of postmastectomy radiotherapy on overall survival in stage II–III node-negative patients following neoadjuvant therapy: A surveillance, epidemiology, and end results-based population study

The necessity of postmastectomy radiotherapy (PMRT) for patients whose initially positive lymph nodes become node-negative (ypN0) after neoadjuvant therapy (NAT) is uncertain. This study analyzed data from the Surveillance, Epidemiology, and End Results database to evaluate PMRT's effect on these patients. Women with unilateral breast cancer who achieved ypN0 status post-NAT from 2010 to 2019 were categorized into PMRT and non-PMRT groups. Propensity score matching (PSM) minimized confounding factors. Statistical tests and multivariate analysis identified survival prognostic factors, while Kaplan-Meier curves and forest plots assessed survival outcomes. The study involved 699 cases, with 458 receiving PMRT and 241 not. After matching, 194 patient pairs were examined. Multivariate analysis revealed stage III disease (hazard ratio: 2.06; 95% CI: 1.12-3.79, <i>p</i> = 0.02) and lack of PMRT (hazard ratio: 2.48; 95% CI: 1.31-4.62, <i>p</i> = 0.01) as independent survival risk factors. PMRT significantly improved overall survival (hazard ratio: 0.43; 95% CI: 0.26-0.72, <i>p</i> < 0.001), especially in patients with clinical node status cN+ (cN1, hazard ratio: 0.47; 95% CI: 0.25-0.88, <i>p</i> = 0.016; cN2-3 hazard ratio: 0.35; 95% CI: 0.15-0.86, <i>p</i> = 0.017, respectively), grade 3 tumors(hazard ratio: 0.47; 95% CI: 0.25-0.88, <i>p</i> = 0.016), stage III disease (hazard ratio: 0.47; 95% CI: 0.26-0.83, <i>p</i> = 0.007), and triplenegative breast cancer (hazard ratio: 0.15; 95% CI: 0.05-0.42, <i>p</i> < 0.001). However, it did not significantly benefit those with grade 1-2 tumors, stage II disease, HER2-positive, or hormone receptor-positive/HER2-negative tumors. The study suggests PMRT may not be necessary for these groups, particularly for HR-positive/HER2-negative grade 1-2 with stage II disease, due to limited short-term benefits.