BACKGROUND: Immunohistochemistry (IHC) for mismatch repair protein expression, microsatellite instability (MSI) testing, tumor morphology, and family history were compared to determine which screening strategy is superior in identifying Lynch syndrome (LS) in unselected women with newly diagnosed endometrial cancer (EC) who have undergone universal germline mutation testing. METHODS: A prospective cohort study was performed that recruited women with newly diagnosed EC. Participants completed a family history assessment with molecular characterization of EC with IHC and MSI testing and EC assessment for LS-associated morphologic features and underwent universal germline mutation testing for mutations in the mismatch repair pathway. The sensitivity, specificity, and positive and negative predictive values were compared between the screening strategies. RESULTS: A total of 118 (65%) of 182 consecutive women with EC participated. Of these, 34 women (29%) had tumors that were IHC deficient and 27 women (23%; N 5 117) had tumors that were positive for MSI. Twenty women (17%) met IHC criteria and 16 women (15.2%, N 5 105) met family history criteria based on Ontario Ministry of Health Criteria for the genetic assessment for LS. Seven women (5.9%) had a germline mutation: 4 had MLH1 (mutL homolog 1), 2 had MSH6 (mutS homolog 6), and 1 had MSH2 (mutS homolog 2). IHC in women aged <60 years had the best performance characteristics, with a sensitivity of 100%, a specificity of 86.1%, a positive predictive value of 58.3%, and a negative predictive value of 100%. Family history and tumor morphology both had the lowest sensitivity at 71.4%. Overall tumor morphology had the poorest performance, with a specificity of 42.1%. CONCLUSIONS: The mutation rate of 5.9% was higher than expected in this unselected cohort of women with EC. The superior screening strategy to identify women presenting with EC is universal IHC screening in women aged <60 years. Cancer 2014;120:3932-9.

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BACKGROUND: For women with ovarian cancer (OC), the optimal screening strategy to identify Lynch syndrome (LS) has not been determined. In the current study, the authors compared the performance characteristics of various strategies combining mismatch repair (MMR) immunohistochemistry (IHC), microsatellite instability testing (MSI), and family history for the detection of LS. METHODS: Women with nonserous and/or nonmucinous ovarian cancer were recruited prospectively from 3 cancer centers in Ontario, Canada. All underwent germline testing for LS and completed a family history assessment. Tumors were assessed using MMR IHC and MSI. The sensitivity, specificity, and positive and negative predictive values of screening strategies were compared with the gold standard of a germline result. RESULTS: Of 215 women, germline data were available for 189 (88%); 13 women (7%) had pathogenic germline variants with 7 women with mutS homolog 6 (MSH6); 3 women with mutL homolog 1 (MLH1); 2 women with PMS1 homolog 2, mismatch repair system component (PMS2); and 1 woman with mutS homolog 2 (MSH2). A total of 28 women had MMR-deficient tumors (13%); of these, 11 had pathogenic variants (39%). Sequential IHC (with MLH1 promoter methylation analysis on MLH1-deficient tumors) followed by MSI for nonmethylated and/or MMR-intact patients was the most sensitive (92.3%; 95% confidence interval, 64%-99.8%) and specific (97.7%; 95% confidence interval, 94.2%-99.4%) approach, missing 1 case of LS. IHC with MLH1 promoter methylation analysis missed 2 patients of LS. Family history was found to have the lowest sensitivity at 55%. CONCLUSIONS: Sequential IHC (with MLH1 promoter methylation analysis) followed by MSI was found to be most sensitive. However, IHC with MLH1 promoter methylation analysis also performed well and is likely more cost-effective and efficient in the clinical setting. The pretest probability of LS is high in patients with MMR deficiency and warrants universal screening for LS. Cancer 2020;126:4886-4894.