Initial screening by immunohistochemistry is effective in universal screening for Lynch syndrome in endometrial cancer patients: a prospective observational study.

Background: Few prospective reports of universal screening for Lynch syndrome exist for patients with endometrial cancer. In this study, we performed immunohistochemical staining for DNA mismatch repair-related genes (MLH1, MSH2, MSH6 and PMS2), to determine the extent to which Lynch syndrome can be diagnosed in endometrial cancer patients through universal screening.

Methods: We recruited 116 consecutive patients assumed to have uterine corpus malignancy from October 2019 to February 2021 in a prospective observational study. We performed immunohistochemical for mismatch repair-related proteins on samples from 100 patients who had surgicopathologically confirmed diagnoses of endometrial cancer. Samples with missing immunohistochemical results for any of the proteins had subsequent universal screening tests for microsatellite instability, DNA methylation of the MLH1 promoter region and mismatch repair genetics.

Results: We identified 19 (19.0%) patients with lost results for any of the proteins. All 19 patient samples had subsequent screening tests. We identified the microsatellite instability-high phenotype in 84.2% (16/19) of these patients and MLH1 methylation in 57.9% (11/19). Mismatch repair genetic testing detected two pathological variants, in MSH2 and MSH6, which indicated that the prevalence of Lynch syndrome was 2.0% in our cohort. Two cases of unclassified variant (MSH6) and one case of benign variant (PMS2) were also detected.

Conclusions: Initial screening by immunohistochemical is an effective method in universal screening for Lynch syndrome in endometrial cancer patients.