Background: Lynch syndrome is caused by germline mismatch repair (MMR) gene mutations. The PREMM1,2,6 model predicts the likelihood of a MMR gene mutation based on personal and family cancer history. Objective: To compare strategies using PREMM1,2,6 and tumour testing (microsatellite instability (MSI) and/or immunohistochemistry (IHC) staining) to identify mutation carriers. Design: Data from population-based or clinic-based patients with colorectal cancers enrolled through the Colon Cancer Family Registry were analysed. Evaluation included MSI, IHC and germline mutation analysis for MLH1, MSH2 , MSH6 and PMS2. Personal and family cancer histories were used to calculate PREMM1,2,6 predictions. Discriminative ability to identify carriers from non-carriers using the area under the receiver operating characteristic curve (AUC) was assessed. Predictions were based on logistic regression models for (1) cancer assessment using PREMM1,2,6, (2) MSI, (3) IHC for loss of any MMR protein expression, (4) MSI+IHC, (5) PREMM 1,2,6+MSI, (6) PREMM1,2,6+IHC, (7) PREMM 1,2,6+IHC+MSI. Results: Among 1651 subjects, 239 (14%) had mutations (90 MLH1, 125 MSH2, 24 MSH6). PREMM1,2,6 discriminated well with AUC 0.90 (95% CI 0.88 to 0.92). MSI alone, IHC alone, or MSI+IHC each had lower AUCs: 0.77, 0.82 and 0.82, respectively. The added value of IHC+PREMM 1,2,6 was slightly greater than PREMM1,2,6+MSI (AUC 0.94 vs 0.93). Adding MSI to PREMM1,2,6+IHC did not improve discrimination. Conclusion: PREMM1,2,6 and IHC showed excellent performance in distinguishing mutation carriers from noncarriers and performed best when combined. MSI may have a greater role in distinguishing Lynch syndrome from other familial colorectal cancer subtypes among cases with high PREMM 1,2,6 scores where genetic evaluation does not disclose a MMR mutation.
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