Introduction/Background To investigate the frequency and clinical significance of Microsatellite Instability (MSI) in endometrial cancer patients.

Methodology The study included 174 patients who underwent total hysterectomy with the diagnosis of endometrial cancer in Hacettepe University Hospital, Department of Obstetrics and Gynecology between January 1, 2019 and March 30, 2021. Loss of expression of DNA mismatch (MMR) proteins was investigated by pathological examination. Patients who were found to be at risk of Lynch syndrome as a result of MMR research were referred to the medical genetics department.

Results The median age of the patients was 60 (min: 35, max: 94). 83.9% of patients were postmenopausal (146/174). The median BMI of the patients included in the study was 30.2 (min: 19.0, max: 54.1). Early stage endometrial cancer was observed in the vast majority of patients (Stage 1A: 54.6%). In the final pathology results, endometrioid adenocarcinoma was the most common with 81%, and serous type cancer was detected in 8% of the patients.

All pathological specimens were analyzed for MMR gene defect. MMR loss was detected in 35.1% of the patients (61/174). The relationship between MMR loss status and histological type is summarized in table 1. In addition, 11.5% (20/174) of the patients in our study were found to be p53 mutants.

Conclusion Today, molecular classification plays a role in the adjuvant treatment plan and prognosis predictions of endometrial cancer. Patients with MMR gene defect, which constitutes 25–30% of endometrial cancers, should be evaluated in terms of Lynch syndrome. In our study, it was found that MMR gene defect is more common in endometrioid type and mixed type endometrial cancers, in line with the literature. Longer follow-up is required for interpretation of survival data.

Disclosures .The authors have no conflict of interest related this research