The clinical relevance of LODDS for post-mastectomy radiotherapy in T1-2N1M0 breast cancer: a real-world propensity score-weighted analysis using the SEER database.

BACKGROUND: The benefit of postmastectomy radiotherapy (PMRT) in patients with T1-2N1M0 breast cancer remains heterogeneous. This study evaluated whether the log odds of positive lymph nodes (LODDS) could stratify PMRT-associated survival benefit in this population. METHODS: This study was designed as a retrospective observational cohort study using data from the Surveillance, Epidemiology, and End Results (SEER) database. Patients with T1-2N1M0 breast cancer who underwent mastectomy between 2010 and 2018 were identified from the SEER database. LODDS was calculated as log [(positive lymph nodes + 0.5)/(negative lymph nodes + 0.5)] and categorized into low, intermediate, and high groups. Inverse probability of treatment weighting (IPTW) was used to balance baseline characteristics. Breast cancer-specific survival (BCSS) and overall survival (OS) were analyzed using Kaplan-Meier curves and Cox regression models. RESULTS: A total of 28,864 patients were included, of whom 12,481 received PMRT and 16,383 did not. After IPTW, baseline characteristics were well balanced. PMRT was associated with improved BCSS [hazard ratio =0.776, 95% confidence interval (CI): 0.723-0.833, P<0.001] and OS (hazard ratio =0.800, 95% CI: 0.759-0.844, P<0.001). The association between PMRT and BCSS differed by LODDS group (P for interaction =0.048). PMRT was not significantly associated with improved BCSS in the low LODDS group (hazard ratio =0.895, 95% CI: 0.779-1.028, P=0.12), but was associated with improved BCSS in the intermediate and high LODDS groups (P<0.001). CONCLUSIONS: PMRT was associated with improved survival in patients with T1-T2N1M0 breast cancer after mastectomy, especially among those with intermediate or high LODDS. LODDS may help refine PMRT decision-making beyond N stage alone.