Locoregional Recurrence After Mastectomy: Risk Factors and Implications for Postmastectomy Radiation.

INTRODUCTION: Locoregional recurrence (LRR) after mastectomy is a critical concern in breast cancer management, although contemporary recurrence patterns in the era of modern systemic therapy and the expanded use of postmastectomy radiation therapy (PMRT) are not well defined. METHODS: We retrospectively reviewed 595 women who underwent mastectomy for invasive breast cancer at a single academic center between 2014 and 2020. Patient demographics, clinicopathologic features, treatments, and outcomes were abstracted from the electronic medical record. Univariable and multivariable Cox proportional hazards regression models were used to identify predictors of LRR and overall recurrence. RESULTS: The median follow-up was 4.8 y. The rate of PMRT in the cohort was 35%, including 78.8% of node-positive patients. Overall, 9.4% of patients experienced recurrence, including 3.4% with LRR (2.7% isolated LRR and 0.7% with distant disease). Estimated 5-y LRR was 3.9%, with an average time to recurrence of 2.6 y. On multivariable analysis, lymphovascular invasion (hazard ratio 6.28, 95% confidence interval 2.30-17.15) and close margins (hazard ratio 3.02, 95% confidence interval 1.15-7.98) were independent predictors of LRR. Nodal status and young age were not associated with increased LRR. Predictors of overall recurrence included higher stage, close/positive margins, and lymphovascular invasion. CONCLUSIONS: In this contemporary cohort, rates of LRR remain low and are consistent with prior reports. Lymphovascular invasion and close surgical margins emerged as independent risk factors for LRR, while nodal status was not significant, likely reflecting adherence to PMRT guidelines. Greater emphasis on margin status and lymphovascular invasion may be warranted when individualizing recommendations for PMRT.