192 The prevalence of lymph node metastasis in low-grade endometrial carcinoma

Introduction/Background The extent of surgery for endometrial carcinoma in Norway depends on preoperative risk-classification based on endometrial biopsy and imaging. With sentinel lymph node biopsy (SLN) replacing lymphadenectomy for nodal assessment, the risk/benefit of surgical staging has changed. We sought to investigate the prevalence of lymph node metastasis in women with low-grade histology. Methodology Women undergoing surgical staging at Oslo University Hospital, a tertiary referral hospital for assumed uterine-confined endometrioid adenocarcinoma with grade 1 or 2 on final pathology from 2006 to 2021 were included. Women were stratified according to myometrial invasion; Results We identified 505 women: 72% underwent lymph node dissection and 28% sentinel lymph node biopsy. Histology was 51% grade 1 and 49% grade 2. Nodal metastasis was detected in 8% of women overall; 3% and 14% for grade 1 and grade 2, respectively (table 1). For nodal metastasis based on grade and myometrial invasion, significantly more women with myometrial invasion ≥50% had nodal metastasis compared to women with myometrial invasion Conclusion The risk of lymph node metastasis in low-grade histology endometrial carcinoma varies significantly based on myometrial invasion. Omitting nodal assessment puts up to 15% of patients with deep myometrial invasion at risk of undetected metastasis and subsequent undertreatment. As surgical staging techniques have evolved, the time has come for implementation of SLN for surgical staging in all women with low-grade endometrial carcinoma, regardless of preoperative risk-assessment. Disclosures See attached files.