Introduction/Background NICE-DG42 set UK standards to test all endometrial cancers for mismatch repair (MMR) deficiency. It's unclear if MMR testing and correct genetic referral for Lynch syndrome testing has been adopted across the UK with reported numbers uncertain. This data is necessary to inform UK health policy makers regarding resources needed and assess compliance with NICE-DG42. The Irish health service has similar MMR testing aims.

Methodology This study audited MMR testing in endometrial cancer at St. James’s Hospital, Ireland. Data was collected from electronic patient records of patients with endometrial cancer discussed at the gynae-oncology MDT from March 2022-March 2023. We reviewed MMR testing, MLH1 hypermethylation studies and Lynch syndrome testing.

Results 128 patients with mean(+/-SD) age of 64(+/-11.2), mean(+/-SD) BMI of 36.7(+/-10.3, 48% recorded) and majority endometrioid histological subtypes (79.7%,n=102), were included. MMR testing was performed in 91.4%(n=117), 30%(n=35) abnormal and 70%(n=82) normal.

100%(n=25) with MLH1/PMS2 loss had hypermethylation testing, all sporadic origins. One had MLH1 loss but hypermethylation details were unavailable (external referral for MDT discussion). One had PMS2 loss and hypermethylation testing suggesting sporadic origin.

MSH2/MSH6 loss was seen in three patients and two had genetics referral. The first had somatic variants, unlikely hereditary. The second did not reveal pathogenic variant (MSH2/MSH6 loss not resolved). Lynch syndrome-like recommendations were made to this family.

MSH6 loss was seen in five patients and three had genetic referral – one was diagnosed with Lynch syndrome and two declined further genetic testing. Two did not have genetic referral (case from different facility; delayed genetic referral post-audit).

Germline testing was performed in four patients and one diagnosed with Lynch syndrome.

Conclusion MMR testing was conducted in majority of patients, with 30% abnormal results. Germline testing, performed in four patients, diagnosed one Lynch syndrome. The findings highlight importance of comprehensive molecular profiling in endometrial cancers, guiding hereditary risk assessment.

Disclosures No conflicts of interest.