Introduction/Background*Universal screening for mismatch repair deficiency (MMRd) in endometrial cancer has been included as a component of the integrated molecular risk assessment and can be used for screening patients with a genetic predisposition for cancer (eg. Lynch syndrome). MMR status is also emerging as an important marker for choosing candidate patients for immunotherapy. We designed a study to evaluate the characteristics of patients with MMR deficient tumours and the impact screening had on their management.

Methodology We included a cohort of consecutively treated women with endometrial cancer in a prospective study between January 2020 to March 2021 at the University Medical Centre Maribor, Slovenia. Cancerous tissue of patients with endometrial cancer was stained using immunohistochemistry (IHC) for the proteins of MMR genes MLH1, PMS2, MSH2 and MSH6. Descriptive statistics are reported in median values (range), categorical variables were evaluated using χ² and continuous variables were evaluated using the Mann-Whitney U test. Statistical analysis was performed using SPSS version 23.

Result(s)*Fourty-five women with EC were identified. Fifteen women (33.3%) had IHC MMRd tumours and 30 women (66.7%) had MMR proficient (MMRp) tumours. Women with MMRd tumours were older (p<.015) with a median age of 72.0 years (49-87) vs. 62.5 years (32-82) and had significantly more frequent deep myometrial invasion (p<.027) as well as lymphovascular space invasion (p<.028) of tumours. There was no significant difference between tumour grade (p>.069). Three women (6.7%) fulfilled traditional criteria for genetic counselling referral. Based on the implementation of universal MMR testing, 15 (33.3%) women with MMRd tumours were additionally identified as candidates for genetic counselling.

Conclusion*Universal MMR testing enables a more personalised risk score and the identification of women with a genetic predisposition for cancer in which EC might present as the »sentinel cancer«. Cost effective screening could improve personalised care and future cancer prevention.