Introduction/Background Sentinel lymph node (SLN) mapping is suggested to be a safe surgical staging method for women with high-risk (grade 3 or non-endometrioid histology) endometrial cancer (EC). However, approximately 20% of women do not have bilateral mapping, leaving a need for consensus on the choice of surgical algorithm in cases of non-mapping. We aimed to assess the safety of SLN mapping algorithms in women with high-risk EC.

Methodology We conducted a national prospective study of SLN mapping in women with high-risk EC from March 2017- January 2023. A power calculation was based on the negative predictive value (NPV) of the SLN algorithm; determining the inclusion of a minimum of 150 women with SLN mapping, pelvic (PLD) and paraaortic (PAA) lymphadenectomy performed. Women underwent SLN mapping, PLD and PAA besides removal of any FDG- PET–positive lymph nodes. Accuracy analyses were applied.

Results We included 216 women. Of these, 170 women had SLN mapping, PLD and PAA performed, and were included in the final accuracy analysis. 42/170 (24.7%) had nodal metastasis. In case of failed mapping, the algorithm with PLD only demonstrated a sensitivity of 88% (95% CI 74–96) and an NPV of 96% (95% CI 91–99). The sensitivity increased to 93% (81–99) and NPV 98% (95% CI 93–100) if PLD and PAA were performed in case of failed mapping. However, equal safety was demonstrated if PLD was performed in case of failed mapping, in combination with removal of any PET-positive lymph nodes: sensitivity 93% (95% CI 81–99), NPV 98% (95% CI 93–100).

Conclusion SLN mapping can be adopted as a safe staging procedure in women with high-risk EC if surgeons strictly adhere to a surgical algorithm in case of failed mapping. This includes either PLD and PAA if pre-operative PET/CT is not performed or PLD and removal of any FDG-positive lymph nodes.

Disclosures The authors have no conflicts of interest to declare.