Adjuvant Therapy in POLE-Mutated and p53-Wildtype/NSMP Early Stage Endometrial Cancer RAINBO BLUE & TAPER

Inclusion Criteria:

* Patients must have had surgery consisting of hysterectomy and bilateral salpingo-oophorectomy. Lymph node dissection can be performed as per institutional standards. There must be no macroscopic residual disease after surgery.
* Patients must have histologically confirmed Stage I to III endometrial carcinoma which can be endometrioid, serous, clear cell, un/dedifferentiated, carcinosarcoma or mixed.
* Patients' Eastern Cooperative Group (ECOG) performance status must be 0, 1, or 2.
* HIV-infected patients on effective anti-retroviral therapy with undetectable viral load within 6 months are eligible for this trial.
* Patients' age must be ≥ 18 years.
* Patient consent must be appropriately obtained in accordance with applicable local and regulatory requirements.
* Patient is able (i.e. sufficiently fluent) and willing to complete the patient-reported outcomes (PRO) questionnaires in either English, French or a validated language
* Patients must be accessible for treatment and follow-up. Patients enrolled on this trial must be treated and followed at the participating centre
* Protocol treatment is to begin within 10 weeks of hysterectomy/bilateral salpingo-oophorectomy

Exclusion Criteria:

* Prior Neoadjuvant chemotherapy for current endometrial cancer diagnosis.
* Prior pelvic radiation.
* Patients with a history of other malignancies, except: carcinoma in-situ without evidence of invasive disease when resected, adequately treated non-melanoma skin cancer, or other tumours curatively treated with no evidence of disease for ≥ 5 years.
* Clinical evidence of distant metastasis as determined by pre-surgical or post-surgical imaging (CT scan of chest, abdomen and pelvis or whole-body PET-CT scan)
* Patients with a documented positive surgical margin.
* Patients with a documented positive peritoneal washings, if performed.