Signatera Assessment in Early-Stage Endometrial Cancer

The goal of this clinical trial is to assess if circulating tumor DNA can guide adjuvant selection in high-intermediate risk early-stage endometrial cancer. The main question it aims to answer is: • To evaluate if 3-year recurrence-free survival among women with Stage I, high-intermediate risk endometrial cancer who are ctDNA negative after receiving ctDNA-guided observation is non-inferior to adjuvant vaginal brachytherapy (an internal radiation therapy) Researchers will compare high-risk intermediate ctDNA negative participants who are observed to those who receive vaginal brachytherapy to see if they have similar outcomes. Participants will be asked to: * Receive serial ctDNA testing * Visit their study doctor per their standard of care visits about every 3 months for 2 years * Answer a questionnaire about their well-being