Are There Patients With T1 to T2, Lymph Node-Negative Breast Cancer Who Are "High-Risk" for Locoregional Disease Recurrence?

BACKGROUND: Indications for postmastectomy radiotherapy (PMRT) in patients with T1 to T2, lymph node-negative (N0) breast cancer with "high-risk" features are controversial. The European Organization for Research and Treatment of Cancer (EORTC) 22922 and National Cancer Institute of Canada Clinical Trials Group MA20 trials reporting improved 10-year disease-free survival with lymph node irradiation included patients with high-risk N0 disease, but, to the authors' knowledge, benefits in patients receiving modern systemic therapy are uncertain. METHODS: The authors retrospectively identified patients with T1 to T2N0 disease who were treated with mastectomy from January 2006 through December 2011. High-risk features included age <40 years, multifocality/multicentricity, lymphovascular invasion, medial/central tumor location, and high nuclear grade. RESULTS: Among 672 eligible patients, only 15 received PMRT and were excluded. Of the remaining 657 patients, 187 (28%) had 1 high-risk feature and 449 patients (68%) had >= 2 high-risk features. A total of 36 patients with unknown tumor grade were excluded from risk analysis. Approximately 98% of patients underwent sentinel lymph node biopsy alone and 86% received adjuvant systemic therapy. At a median of 5.6 years of follow-up, the locoregional disease recurrence (LRR) rate was 4.7% (31 patients). Increasing tumor size was found to be associated with LRR (hazard ratio, 1.70; P = .006), whereas other high-risk features were not (all P > .05). Receipt of systemic therapy decreased the LRR rate (hazard ratio, 0.40; P = .03). Although crude LRR rates increased from 3.8% to 9.4% with 1 versus >= 4 high-risk features, the number of risk factors was not found to be significantly associated with LRR (P = .54). CONCLUSIONS: In the current study, a low crude LRR rate (4.7%) was observed in a large unselected cohort of patients with T1 to T2N0 breast cancer with high-risk features who were treated with mastectomy and systemic therapy without PMRT. Although increasing tumor size and the omission of systemic therapy were found to be predictive, other features did not confer a higher LRR risk either independently or together, and do not by themselves mandate the use of PMRT in this patient population. (C) 2017 American Cancer Society.