Testing for Lynch Syndrome in Endometrial Carcinoma: From Universal to Age-Selective MLH1 Methylation Analysis

International guidelines recommend universal screening of endometrial carcinoma (EC) patients for Lynch syndrome (LS). This screening is generally based on mismatch repair (MMR) protein immunohistochemistry followed by MLH1 methylation analysis of MLH1-negative cases to exclude the likely sporadic cases from germline testing. As LS-associated EC is uncommon in the elderly, age-selective methylation testing could improve cost-efficiency. We performed MMR immunohistochemistry on 821 unselected ECs (clinic-based cohort) followed by a MLH1 promoter methylation test of all MLH1/PMS2-negative tumors. Non-methylated MLH1-deficient cases underwent NGS and MLPA-based germline analyses to identify MLH1 mutation carriers. A reduction in the test burden and corresponding false negative rates for LS screening were investigated for various age cut-offs. In addition, the age distribution of 132 MLH1 mutation carriers diagnosed with EC (registry-based cohort) was examined. A germline MLH1 mutation was found in 2/14 patients with non-methylated MLH1-deficient EC. When compared to a universal methylation analysis, selective testing with a cut-off age of 65 years, would have reduced the testing effort by 70.7% with a false negative rate for LS detection of 0% and 3% in the clinic and registry-based cohorts, respectively. The use of age-selective methylation analysis is a feasible way of reducing the costs and laboratory burden in LS screening for EC patients.