Abstract
Purpose: Breast cancer is a heterogeneous disease and not all patients respond equally to adjuvant radiotherapy. Predictive biomarkers are needed to select patients who will benefit from the treatment and spare others the toxicity and burden of radiation.Experimental Design: We first trained and tested an intrinsic radiosensitivity gene signature to predict local recurrence after radiotherapy in three cohorts of 948 patients. Next, we developed an antigen processing and presentation-based immune signature by maximizing the treatment interaction effect in 129 patients. To test their predictive value, we matched patients treated with or without radiotherapy in an independent validation cohort for clinicopathologic factors including age, ER status, HER2 status, stage, hormone-therapy, chemotherapy, and surgery. Disease-specific survival (DSS) was the primary endpoint.Results: Our validation cohort consisted of 1,439 patients. After matching and stratification by the radiosensitivity signature, patients who received radiotherapy had better DSS than patients who did not in the radiation-sensitive group [hazard ratio (HR), 0.68; P = 0.059; n = 322], whereas a reverse trend was observed in the radiation-resistant group (HR, 1.53; P = 0.059; n = 202). Similarly, patients treated with radiotherapy had significantly better DSS in the immune-effective group (HR, 0.46; P = 0.0076; n = 180), with no difference in DSS in the immune-defective group (HR, 1.27; P = 0.16; n = 348). Both signatures were predictive of radiotherapy benefit (P (interaction) = 0.007 and 0.005). Integration of radiosensitivity and immune signatures further stratified patients into three groups with differential outcomes for those treated with or without radiotherapy (P (interaction) = 0.003).Conclusions: The proposed signatures have the potential to select patients who are most likely to benefit from radiotherapy. Clin Cancer Res; 24(19); 4754-62. ©2018 AACR.