# Diagnostic Accuracy and Interrater Agreement of FDG-PET/CT Lymph Node Staging in High-Risk Endometrial Cancer: The SENTIREC-Endo Study

## TL;DR

FDG-PET/CT scans help detect lymph node cancer spread in high-risk endometrial cancer patients but are best used with surgical methods for accurate diagnosis.

## Contribution

The study confirms FDG-PET/CT's role as a complementary tool for lymph node staging when combined with sentinel lymph node mapping in high-risk endometrial cancer.

## Key findings

- FDG-PET/CT showed 56% sensitivity and 91% specificity for detecting lymph node metastases.
- High interrater agreement (95% agreement, κ = 0.84) was observed among specialists evaluating FDG-PET/CT scans.
- FDG-PET/CT is recommended for clinical use alongside sentinel node biopsy to guide targeted dissection of PET-positive nodes.

## Abstract

This study looked at how well FDG-PET/CT scans detect cancer spread to lymph nodes in women with high-risk endometrial cancer. It included 227 women undergoing treatment at three Danish hospitals. The scans correctly identified lymph node spread in many patients, especially along the major vessels, but were less reliable in finding all cases where cancer had spread to the lymph nodes. Specialists from different hospitals largely agreed on which lymph nodes looked suspicious, showing that the method was consistent across hospitals. While FDG-PET/CT alone cannot replace surgical staging, we confirmed that it added value when used alongside the sentinel lymph node mapping surgical procedure. The combined approach allows doctors to better identify the nodes that need removal for investigation, while avoiding unnecessary surgery with the removal of all lymph nodes. The findings support implementing FDG-PET/CT as part of a focused strategy of optimal lymph node staging in high-risk endometrial cancer.

Background/Objectives: The SENTIREC-endo study identified a safe sentinel lymph node mapping algorithm combined with PET-positive node dissection, matching radical pelvic and paraaortic lymphadenectomy in high-risk endometrial cancer. The present study evaluated the diagnostic accuracy of FDG-PET/CT for lymph node metastases in the same population based on location, size, and Standardised Uptake Value (SUV), in addition to assessing interrater agreement across three Danish centres. Methods: This prospective multicentre study included women with high-risk endometrial cancer from the Danish SENTIREC study database (2017–2023). All patients underwent preoperative FDG-PET/CT. Diagnostic accuracy was evaluated against a pathology-confirmed reference standard. Interrater agreement was evaluated between trained specialists in Nuclear Medicine. Results: Among 227 patients, 52 patients (23%) had lymph node metastases. FDG-PET/CT identified lymph node metastases with 56% sensitivity (95% CI: 42–68) and 91% specificity (95% CI: 86–94). Positive and negative predictive values were 64% and 87%, respectively. Specificity for paraaortic nodes was high (97%), though sensitivity remained limited (56%). Lymph node size and SUVmax had moderate diagnostic value (AUC-ROC ~0.7). Interrater proportion of agreement was 95% and Cohen’s Kappa κ = 0.84 (95% CI: 0.73–0.94), the latter of which was ‘almost perfect’. Conclusions: FDG-PET/CT had limited sensitivity in lymph node staging in high-risk EC, and the diagnostic accuracy of FDG-PET/CT remains complementary to the sentinel node procedure. Due to its high specificity and strong interrater reliability, FDG-PET/CT is recommended for clinical implementation in combination with the sensitive sentinel node biopsy for the targeted dissection of PET-positive lymph nodes, particularly in paraaortic regions.