Role of Adjuvant Brachytherapy and External Beam Radiotherapy in Women With High-Risk Stage I Endometrial Cancer [ID 1570]

INTRODUCTION: Endometrial cancer is the most common gynecological cancer in the United States, with rising global incidence. Papillary serous and clear cell carcinomas are high-risk, aggressive histologies. Most radiation therapy studies exclude these rare histologies, leading to debate about optimal treatment approaches. This study compares survival outcomes of radiation modalities in patients with localized (FIGO stage I) papillary serous and clear cell endometrial carcinoma to contribute to evidence guiding radiation therapy decisions. METHODS: The Surveillance, Epidemiology, and End Results (SEER) data (2000–2016) included females with localized papillary serous or clear cell endometrial carcinoma. Patients received external beam radiation therapy (EBRT), brachytherapy, or combined EBRT and brachytherapy. Fine-Gray subdistribution hazard models assessed the effect of radiation modality and age on 5-year and 10-year survival. RESULTS: Higher age was significantly associated with an increased risk of death within 5 years (n=446), with a hazard ratio (HR) of 1.02 (95% CI, 1.00–1.04; P =.037) per year increase in age. At 5 years, brachytherapy showed superior survival compared to EBRT and combination therapy; with an HR of 0.44 (95% CI, 0.26–0.74; P = 0.0021) versus EBRT. Similar results were observed at 10 years (n=331). CONCLUSIONS/IMPLICATIONS: Brachytherapy alone is associated with a significant survival advantage over EBRT and combination therapy in localized papillary serous or clear cell endometrial carcinoma. These findings suggest brachytherapy may be preferred for these high-risk histologies in localized disease, aiding clinical decision-making and potentially improving patient outcomes. Further research considering the effect of systemic therapy and other patient factors is warranted to guide best practices.