<h3>Purpose/Objective(s)</h3> The 17-gene genomic prostate score (GPS) assay is a prognostic tool that evaluates gene expression from prostate cancer (PC) biopsy tissue and generates a score between 0 to 100, with higher scores indicating more aggressive disease. The GPS assay is validated as a strong predictor of adverse outcomes in men with localized PC after prostatectomy. For patients treated with external beam radiation therapy (EBRT), a genomic assay using core needle biopsy tissue that predicts risk of PC progression could inform decisions regarding treatment intensity. Here, we analyzed whether GPS results are associated with time to biochemical failure (BCF), distant metastasis (DM), and prostate cancer related death (PCD) after EBRT for localized PC and, if so, whether the association is modified by race. <h3>Materials/Methods</h3> We conducted a retrospective study on men with localized PC treated with EBRT at an equal-access academic health center from 2000 to 2016. Patients were treated per standard of care with <i>post hoc</i> GPS assay analysis. Endpoints investigated were time to BCF per the Phoenix criteria, DM, and PCD. The association of GPS result with each endpoint was evaluated using multivariable Cox proportional hazards models. Results were then stratified by race. <h3>Results</h3> A total of 238 patients met eligibility criteria; 69% were Black. The National Comprehensive Cancer Network (NCCN) risk group distribution was: 30% very low, low, or favorable intermediate; 37% unfavorable intermediate; 21% high; 11% very high. Median follow-up for patients who did not experience BCF was 7.6 years. The GPS result, when stratified by 20 units, was significantly associated with BCF, DM, and PCD in multivariable analysis, adjusted for NCCN risk group (Table 1). Similar results were observed with a dichotomous GPS result. There was no significant interaction between the GPS assay and race (p=0.923). HRs for BCF were similar in AA men (HR 3.88; 95% CI 2.40-6.24) versus non-AA men (HR 4.01; 95% CI 2.42-6.45). <h3>Conclusion</h3> Among men treated with EBRT, the GPS assay is a strong, independent predictor of time to BCF, DM and PCD. In patients with unfavorable intermediate-risk PC and higher, the GPS assay can stratify risk beyond the NCCN categories, identifying patients who could be candidates for treatment (de)intensification. The results also suggest that the association between the GPS result and long-term outcomes is independent of race.