Introduction: In the past years, there has been a rise on advanced endometrial cancers (EC) patients resulting in mortality increase. To overcome this trend, it is essential to improve the stratification of the risk of post-surgery recurrence and to anticipate the development of disease relapse and resistance to treatment. Liquid biopsy analyses represent a promising tool to address these clinical challenges, however, the best strategy to efficiently apply them in the context of EC must be better defined. Therefore, the study was designed to determine the value of cfDNA/ctDNA monitoring to improve the clinical management of patients with localized and recurrent disease. Material & Methods: Plasma samples and the uterine aspirate (UA) from 198 patients with EC were collected in different Spanish hospitals at surgery and throughout the course of the disease. The genetic landscape of UAs was characterized using targeted sequencing. Total cfDNA was isolated from all plasma samples, quantified, and analysed for the presence of ctDNA based on the mutational profile found on the UAs. Results: The genetic characterization of UAs obtained at surgery allowed the identification of pathogenetic variants in the 95,45% of the tumours and ctDNA levels could be monitored in the 89,4% of the patients. High levels of cfDNA and detectable levels of ctDNA at baseline correlated with poor prognosis, for both DFS (p-value<0.0001; HR=9,25) and DSS (p-value<0.0001; HR=11,20). Importantly, this approach remains clinically significant when stratifying tumours based on histopathological risk factors, highlighting its additional value to identify patient with a poor evolution. In fact, cfDNA/ctDNA analysis served to identify patients who showed early post-surgery relapse. Moreover, longitudinal analyses of cfDNA/ctDNA proved to be a powerful asset to identify patients undergoing relapse, months prior to the arisen of any clinical evidence. Conclusion: This study represents the most comprehensive study on cfDNA/ctDNA characterization in EC and demonstrates its value to improve the risk stratification and anticipate the disease relapse in patients with localized disease. Besides, the dynamic ctDNA assessment showed utility to complement the current strategies to monitor disease evolution and the response to treatment. Implementation of cfDNA/ctDNA monitoring into the clinical routine will provide an unique opportunity to improve EC management

The authors have declared no competing interest.

This work has been supported by the Instituto de Salud Carlos III (ISCIII) and FEDER (PI20/00969 and PI20/01566) -AGM, MA-, (PI21/00990) -LMR-; the Ministerio de Ciencia, Innovacion y Universidades, Agencia Estatal de Investigacion (PID2022-136854OB-I00) -GMB-, the CIBERONC (CB16/12/00328 -LM-EC-AGM-MA-, CB16/12/00295 -GMB-) and the Fundacion cientifica AECC (FCAECC, GCTRA1804MATI) -AGM, MA and GMB-, Proyectos de Excelencia (IN607D2021/05) -LM- and ERA PerMed ERA-NET cofunded by the European Union, NextGeneration-EU through Instituto de Salud Carlos III (ISCIII) and FCAECC (AC21_2/00020) -GMB-LMR-. LMR and EC are supported by a contract "Miguel Servet" from ISCIII (CP20/00119, CP22/00147, respectively). SO is funded by an FCAECC-postdoctoral grant (PI21/00990). CCA is funded by an IDIS-predoctoral grant (2020). JRB is supported by a Juan Rodes contract (JR21/00019) from the Institute of Health Carlos III.

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The study was approved by the corresponding Research Ethics Committees (Galician Research Ethics Committee reference number 2017/530 and 2022/029, Vall d'Hebron Research Ethics Committee reference number PRAMI276-2018) and conducted in accordance with the guidelines for Good Clinical Practice and the Declaration of Helsinki. All patients provided written informed consent before enrolment.

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