Real-world impact of postmastectomy radiotherapy in T1–2 breast cancer with one to three positive lymph nodes

BACKGROUND: The utility of postmastectomy radiotherapy (PMRT) in breast cancer patients with T1–2 (tumor size ≤5 cm) and N1 (one to three lymph nodes involved) disease remains controversial. The aim of this population-based study was to investigate the effectiveness of PMRT in this patient subset in the current clinical practice. METHODS: We included T1–2N1 breast cancer patients treated with mastectomy from 2004 to 2012 using the data form the Surveillance, Epidemiology, and End Results program. The association of PMRT administration with breast cancer-specific survival was determined using multivariable Cox analysis. RESULTS: We identified 10,248 patients of this study, including 3,725 (36.3%) received PMRT and 6,523 (63.7%) patients did not receive PMRT. Use of PMRT showed increase from 2008 onward; the percentage of patients receiving PMRT was 30.6% in 2004 and was 47.1% in 2012 (P<0.001). Patients diagnosis after 2008, aged <50 years, high tumor grade, T2 stage, and ≥2 positive lymph nodes were independently related to PMRT receipt. Multivariate analysis indicated that PMRT was not related to better breast cancer–specific survival compared to those without PMRT both before (P=0.186) and after propensity score matching (P=0.137). CONCLUSIONS: In breast cancer with T1–2N1 disease, PMRT does not appear to improve survival in the era of modern systemic therapy.