SEntinel Lymph Node Endometrial Cancer Trial: A Prospective Multicenter International Single-Arm Observational Trial (SELECT)

Screening Inclusion Criteria: * ECOG performance status 0-1 or KPS ≥ 70% * Age ≥ 18 years * Endometrioid adenocarcinoma histologic diagnosis on endometrial biopsy or dilatation and curettage * No evidence of extrauterine disease, or suspicious pelvic lymph nodes, or distant metastases, or cervical invasion on pre-operative conventional imaging studies (Pelvic +/- Abdomen CT or MRI or sonogram, or body PET scan) and physical examination (uterine confined by exam and imaging ) * Suitable candidate for surgery * Planned surgical treatment including hysterectomy in combination with SLN biopsy and a bilateral salpingo-oophorectomy * No history of second primary cancer (invasive or in situ) within the past 5 years, not including non-melanoma skin cancer * Approved and signed informed consent * No history of neoadjuvant chemotherapy or radiotherapy for endometrial cancer * No history of prior pelvic or abdominal radiotherapy Screening Exclusion Criteria: * Extrauterine disease, or gross lymph node involvement, or cervical invasion suspected on pre-operative imaging studies and physical examination (disease not uterine confined clinical stage \> I) * Contraindication for SLN mapping * The planned treatment is not surgery, or the surgical treatment does not include hysterectomy in combination with SLN biopsy and a bilateral salpingo-oophorectomy Eligibility Inclusion Criteria Patients will be classified in the study cohort (part 2; n=182) according to surgical treatment received, final post hysterectomy and staging pathologic report, and planned adjuvant treatment. The inclusion criteria are specified below. Study Cohort (n=182) A patient will be enrolled in the study cohort if all the following criteria are met: * At surgery, the patient must undergo: * Hysterectomy * Bilateral salpingo-oophorectomy, unless already performed (including allowing unilateral salpingo-oophorectomy if unilateral salpingo-oophorectomy already performed) * Bilateral pelvic SLN mapping (bilateral sentinel nodes are negative for malignancy) * On the final pathologic report, the patient must have a diagnosis of: * Stage I intermediate-risk endometrial endometrioid cancer (Grade 1 or Grade 2 with ≥ 50% myometrial invasion or Grade 3 with \<50% myometrial invasion, including non-invasive disease) * Negative pelvic peritoneal cytology * Adjuvant treatment as recommended by the multidisciplinary team must be as follows: * No adjuvant treatment, or * Intravaginal radiation only Eligibility Exclusion Criteria * There is intra-operative detection of extra-uterine disease or grossly involved lymph nodes * Presence of any positive pelvic nodes including micrometastasis and isolated tumor cells (ITC) * Hysterectomy is not performed * Bilateral salpingo-oophorectomy is not performed, unless already performed (unilateral salpingo-oophorectomy is allowed if unilateral salpingo-oophorectomy already performed) * Failed unilateral or bilateral SLN mapping * Patient undergoes a complete unilateral or bilateral pelvic lymphadenectomy * Patient undergoes a radical type C hysterectomy * Stage IA endometrioid cancer Grade1 or 2 and myometrial invasion \<50% * Stage IB Grade 3 endometrioid cancer * Non-endometrioid histology: Serous, clear cell, carcinosarcoma, undifferentiated, or de-differentiated histology noted on final hysterectomy pathology * Empty unilateral or bilateral sentinel lymph nodal packet(s) * Positive peritoneal cytology