Outcomes and utilization of postmastectomy radiotherapy for T3N0 breast cancers.

BACKGROUND: The role of postmastectomy radiotherapy (PMRT) for women with pT3N0M0 breast cancer is controversial. We sought to determine the benefit of PMRT in this cohort using the National Cancer Database (NCDB).

METHODS: We analyzed women with pT3N0M0 breast cancer who received mastectomy with or without PMRT between 2004 and 2012. We excluded men, women ≤18 years, neoadjuvant or unknown radiation or chemotherapy status, unknown estrogen or progesterone receptor status, unknown surgical margin status, histology other than invasive ductal or lobular carcinoma, and if death occurred <3 months after diagnosis. A total of 4291 patients was included for analysis. Chi-squared analysis was used to compare patient characteristics. Univariate (UVA) and multivariate (MVA) Cox proportional hazards modeling was used to identify factors associated with survival. Propensity score matching was performed to address confounding variables. Survival analysis was performed using Kaplan-Meier and shared frailty models.

RESULTS: Of the 4291 women analyzed, 2030 (47%) received PMRT. On MVA, PMRT (HR 0.72, p < 0.001), chemotherapy (HR 0.51, p < 0.001), and hormone therapy (HR 0.63, p < 0.001) were associated with improved overall survival (OS). After propensity score matching, a matched cohort of 2800 women was analyzed. At 5 years, OS was 83.7% and 79.8% with and without PMRT, respectively (p < 0.001). This difference in OS benefit increased with time. At 10 years, OS was 67.4% and 59.2% with and without PMRT, respectively.

CONCLUSIONS: PMRT was associated with improved OS in women with pT3N0M0 breast cancer, which strongly suggests PMRT may provide a survival advantage and should be considered.