controlling for patient age, diagnosis year, race/ethnicity, stage, grade, number of positive regional lymph nodes, and tumor size.Results A total of 2,362 patients were identified. A significant improvement in cause specific survival (CSS) was noted in patients who underwent combination therapy (vaginal brachytherapy [VB] plus external beam radiation therapy [EBRT]) versus chemotherapy alone (hazard ratio [HR] 0.805, 95% confidence interval [CI] 0.674-0.961, p<0.05). VB and EBRT each given exclusively versus chemotherapy alone resulted in improved overall survival (OS) ([VB HR 0.852, 95% CI 0.788-0.920, p<0.001], [EBRT HR 0.758, 95% CI 0.646-0.889, p=0.001]), but not cause specific survival (CSS). No difference in survival was found in VB or EBRT alone versus combination therapy, or in EBRT versus VB. Conclusions Combination aRT with chemotherapy shows superior CSS compared to chemotherapy alone. This SEER database study validates aRT use in this rare subset of high-risk endometrial cancer.