Blood test may spare some women from radiation after endometrial cancer surgery

Copied word for word from the study's registry entry, so the wording is the study team's rather than ours.

Inclusion Criteria: General inclusion criteria includes the following selection criteria to be eligible for inclusion in any aspect of the study. Eligibility will be assessed by the investigator: 1\. Signed and dated informed consent form (ICF) obtained prior to any trial-specific enrollment procedure. 2\. Patient is ≥ 18 years-old at the time of ICF signature. 3. Able to submit sufficient residual tissue obtained per standard of care procedures. HIR patients must meet all the following selection criteria to be eligible for the randomization cohort in the study. Eligibility will be assessed by the investigator: 1. FIGO 2009 Stage I after hysterectomy and lymph node assessment by bilateral pelvic lymphadenectomy or SLND 1. If para-aortic lymph nodes are not pathologically assessed, documentation of surgical assessment or imaging is recommended. 2. Stage I patients with endometrioid histology: 1. Age 70 years or older with one uterine risk factor, 2. Age 50-69 years with two risk factors, 3. Age 18 - 49 years with three risk factors. Uterine risk factors include: * Grade 2 or 3 tumor. * Outer half depth of invasion. * Lymphovascular invasion. Note: peritoneal cytology must be negative if performed. Patients must meet all the following selection criteria to be eligible for the observation arms of the study. Eligibility will be assessed by the investigator following hysterectomy and lymph node assessment by bilateral pelvic and para-aortic lymphadenectomy or SLND: 1\. High risk cohort a. FIGO 2009 Stage I with high risk histology i. Defined as serous, clear cell, carcinosarcoma, or mixed histology. 1. Negative peritoneal cytology, where performed (recommended) 2. If para-aortic lymph nodes are not pathologically assessed, imaging is required b. FIGO 2009 Stage II Endometrioid 2\. Low risk cohort a. FIGO 2009 Stage I patients at low risk of recurrence i. Endometriod histology ii. Absent uterine risk factors, or present but insufficient to meet HIR criteria Exclusion Criteria: Patients are not eligible for the study if they meet any of the following criteria, as assessed by the investigator: 1. Undifferentiated or dedifferentiated histology 2. Uterine sarcoma 3. Prior pelvic radiation therapy 4. Positive pelvic washings 5. Pelvic lymph node assessment was not performed 6. Isolated Tumor Cells (ITC) identified in the lymph node(s) 7. Prior therapy for endometrial cancer (including hormonal therapy, chemotherapy, targeted therapy, immunotherapy) a. Contraceptives or other hormonal management for endometrial intraepithelial hyperplasia is allowed 8. Patients with a history of other invasive malignancies, with the exception of non-melanoma skin cancer, are excluded if there is any evidence of active malignancy within the last five years. a. Patients are also excluded if their previous cancer treatment contraindicates this protocol therapy. 9. Patients with a history of serious comorbid illness or uncontrolled illnesses that would preclude protocol therapy. 10. Patients with a history of myocardial infarction, unstable angina, or uncontrolled arrhythmia within 3 months from enrollment. 11. Previous diagnosis of Crohn's disease or ulcerative colitis. 12. Patient is currently receiving, or plans to receive, commercial ctDNA/MRD assay for disease monitoring, excluding Signatera. Patients must agree to forego testing with assays other than Signatera Genome upon enrollment until end of study.