Risk Factors for Locoregional Recurrence After Mastectomy in Stage T1 N0 Breast Cancer

Objectives: Postmastectomy radiotherapy (PMRT) is proven to decrease locoregional recurrence (LRR) in locally advanced breast cancer. However, there is little data regarding PMRT in early stage disease. This study examines risk factors for LRR in patients who underwent mastectomy for T1 N0 breast cancer, with the aim of identifying a subgroup who may potentially benefit from PMRT., Methods: From 1994 to 2004, there were 1259 pathologic stage T1 N0 breast cancers treated with mastectomy and no radiation within the Kaiser Permanente Southern California medical system. Kaplan-Meier survival curves for LRR were compared using the log-rank test, and multivariate analysis was done using Cox proportional hazard ratios to identify risk factors for LRR. Results: Median follow-up was 8.15 years. The 10-year Kaplan-Meier LRR rate was 3.2% (95% confidence interval [CI], 2%-4.3%). The median time to LRR was 2.5 years after mastectomy, and the most common site was chest wall (68%). Grade 3 (hazard ratio 3.97; 95% CI, 1.94-8.14; P=0.0002) and margins <= 3 mm (hazard ratio 2.97; 95% CI, 1.21-7.29; P=0.02) were significantly associated with LRR on multivariate analysis. The 10-year Kaplan-Meier rate of LRR for the 1230 patients with neither or one factor was 2.7% (95% CI, 1.6%-3.8%), compared with a LRR rate of 25% (95% CI, 2.2%-42.7%) among the 29 patients with both high grade and margins <= 3 min (P < 0.0001). Conclusions: After mastectomy for pT1 N0 breast cancer, there is a small subgroup of patients with grade 3 disease and a close or positive margin (3 mm) who have an increased risk of LRR. These patients may benefit from the administration of PMRT.