Soluble immune checkpoints in endometrial cancer – a discovery study

Boštjan Pirš^1,2Maja Pušić Novak³Luka Roškar^2,4Tea Lanišnik Rizner^3*Špela Smrkolj^1,2*

• ¹Department of Gynaecology, Division of Gynaecology and Obstetrics, University Medical Centre Ljubljana, Ljubljana, Slovenia
• ²Faculty of Medicine, University of Ljubljana, Ljubljana, Slovenia
• ³Laboratory for Translational Molecular Endocrinology, Institute of Biochemistry and Molecular Genetics, Faculty of Medicine, University of Ljubljana, Ljubljana, Slovenia
• ⁴Department of Gynaecology and Obstetrics, General Hospital Murska Sobota, Murska Sobota, Slovenia

Background Soluble immune checkpoints (sICs) are circulating forms of membrane-bound immune molecules, the latter being targets of immune checkpoint inhibitors, widely used in cancer treatment. Altered sIC levels have been reported in several malignancies and sICs are posited as promising diagnostic, prognostic and predictive biomarkers measurable in peripheral blood. However, data on their levels in endometrial cancer (EC) patients are scarce. This study aimed to evaluate plasma concentrations of multiple sICs in EC patients and assess their potential diagnostic, prognostic, and predictive value. Methods In this prospective case–control study, plasma levels of 16 soluble immune checkpoints were measured in 50 patients with histologically confirmed EC prior to surgical staging and in 26 age-and BMI-matched controls undergoing benign gynecologic surgery. Fluorescence-based multiplex immunoassay (MagPix, Luminex) was used to quantify analyte concentrations. FIGO 2023 stage classification and risk grouping according to ESGO 2020 guidelines was performed based on clinicopathologic data and molecular characteristics (MMR and p53 status). Statistical analyses were performed using non-parametric tests and robust logistic regression. Results EC and control groups did not differ in demographic, clinical, or lifestyle parameters. sIC levels were measurable in majority of patients. No significant differences in sIC levels were observed between EC patients and controls. Within the EC cohort, patients with MMR-deficient tumors exhibited significantly elevated levels of sPD-1, sPD-L1, sLAG-3, sICOS, sGITR, and sCD86 compared with MMR-proficient cases. Higher plasma concentrations of sTIM-3, sCD27, sHVEM, and sCD40 were associated with the presence of lymphovascular space invasion (LVSI). Levels of sCD27 and sCD40 were significantly higher in advanced or metastatic disease (stage IIIA or higher). Conclusions Although soluble immune checkpoint levels did not differentiate EC patients from controls, several sICs correlated with key prognostic and predictive features, including LVSI, advanced stage, and MMR deficiency. These findings suggest that circulating immune checkpoint proteins may serve as non-invasive biomarkers for risk assessment and immunotherapy response prediction in endometrial cancer. Further validation in larger, independent cohorts is warranted.