Role of 21-Gene Recurrence Score in Predicting Prognostic Benefit of Radiation Therapy After Breast-Conserving Surgery for T1N0 Breast Cancer

Purpose: The 21-gene RT-PCR recurrence score (RS) is performed in patients with hormone receptor–positive (ER+, PR+), human epidermal growth factor receptor 2 (HER2)–negative, N0 breast cancer to determine which patients will likely benefit from chemotherapy after breast-conserving surgery (BCS). The purpose of this study was to evaluate whether the RS can predict for patients likely to benefit from radiation therapy (RT) after BCS. Methods and Materials: The National Cancer Database was queried (2004-2017) for female patients with pT1N0 ER+ PR+ HER2-negative breast cancer treated with BCS who had an available RS. Patients were stratified based on their RS (low risk [LR], 1-10; intermediate risk [IR], 11-25; high risk [HR], 26-100). For each RS cohort, propensity score matching was conducted to create 1:1 matched cohorts of patients who received RT and patients who did not. Kaplan-Meier analysis evaluated overall survival (OS). Univariable and multivariable (MVA) Cox proportional hazard analysis identified clinical and treatment factors prognostic for OS. Results: A total of 79,040 patients met the selection criteria: 18,823 in the LR cohort, 52,341 in the IR cohort, and 7876 in the HR cohort. A total of 92% of patients received RT: 91% in the LR cohort, 93% in the IR cohort, and 92% in the HR cohort. After propensity score matching, the 5-year OS in the LR cohort was 95% for those who received RT and 93% for those who did not (P = .184). In the IR cohort, the 5-year OS was 95% for those who received RT and 93% for those who did not (P = .001). In the HR cohort, the 5-year OS was 95% for those who received RT and 84% for those who did not (P < .001). MVA demonstrated that RT was a positive prognostic factor for OS in both the IR cohort (P = .001) and HR cohort (P < .001). On MVA in the LR cohort, RT (P = .186) was not predictive of improved OS. Conclusions: An OS benefit was observed with the use of RT in patients with IR or HR RS but not in patients with LR RS. Future prospective evaluation is warranted.