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Lynch syndrome is the most common inherited colorectal cancer syndrome, accounting for 2-4% of all colorectal cancer cases. This review focuses on the tissue workup of Lynch syndrome, including methods to determine whether or not a tumor is mismatch repair deficient, and whether a mismatch repair-deficient tumor is sporadic or Lynch syndrome-associated. Strategies for determining which tumors to test and how best to implement a Lynch syndrome screening program are also discussed, as well as potential developments in the future.

Lynch syndrome is characterized by mutations in one of four mismatch repair genes, MLH1, MSH2, MSH6, or PMS2. Clinical mutation analysis of these genes includes sequencing of exonic regions and deletion/duplication analysis. However, detection of deletions and duplications in PMS2 has previously been confined to Exons 1-11 due to gene conversion between PMS2 and the pseudogene PMS2CL in the remaining 3' exons (Exons 12-15). We have recently described an MLPA-based method that permits detection of deletions of PMS2 Exons 12-15; however, the frequency of such deletions has not yet been determined. To address this question, we tested for 3' deletions in 58 samples that were reported to be negative for PMS2 mutations using previously available methods. All samples were from individuals whose tumors exhibited loss of PMS2 immunohistochemical staining without concomitant loss of MLH1 immunostaining. We identified seven samples in this cohort with deletions in the 3' region of PMS2, including three previously reported samples with deletions of Exons 13-15 (two samples) and Exons 14-15. Also detected were deletions of Exons 12-15, Exon 13, and Exon 14 (two samples). Breakpoint analysis of the intragenic deletions suggests they occurred through Alu-mediated recombination. Our results indicate that ∼12% of samples suspected of harboring a PMS2 mutation based on immunohistochemical staining, for which mutations have not yet been identified, would benefit from testing using the new methodology., (Copyright © 2012 Wiley Periodicals, Inc.)

Objective: To characterize the current state of evidence and apply simulation modeling to support decision making about provision and coverage of a Lynch syndrome (LS) screening program among colorectal cancer (CRC) patients in our integrated healthcare delivery system., Study Design: Application of multiple methods for synthesizing evidence guided by needs of our clinical and administrative decision makers., Methods: Narrative and focused reviews, computerized simulation models of multiple screening options, queries of our electronic data warehouse, and extensive communication with decision makers., Results: Review of published evidence at the time of the study period revealed that screening unselected CRC patients for LS would likely cost less than $25,000 per life-year saved (compared with no screening) and that screening with immunohistochemistry is substantially more efficient than other options. Our simulation models suggest that not only does including BRAF mutation testing substantially improve efficiency but that adding methylation testing improves it further. We characterized a variety of other metrics that contributed not only to local decisions but to the broader evidence base on this topic., Conclusion: The current state of evidence at the time of the study period suggests an LS screening program can be both effective in reducing mortality from CRC and cost-effective. However, direct evidence remains limited and multiple factors could threaten success of such a program. We have identified opportunities for optimizing the efficiency of available screening protocols. While there was enough evidence for our system to proceed with an LS screening program, we recognize the threats to program success and will prospectively collect outcome data supporting empirical examination of the program.

Germline mutation detection in PMS2, one of four mismatch repair genes associated with Lynch syndrome, is greatly complicated by the presence of numerous pseudogenes. We used a modification of a long-range PCR method to evaluate PMS2 in 145 clinical samples. This modification avoids potential interference from the pseudogene PMS2CL by utilizing a long-range product spanning exons 11-15, with the forward primer anchored in exon 10, an exon not shared by PMS2CL. Large deletions were identified by MLPA. Pathogenic PMS2 mutations were identified in 22 of 59 patients whose tumors showed isolated loss of PMS2 by immunohistochemistry (IHC), the IHC profile most commonly associated with a germline PMS2 mutation. Three additional patients with pathogenic mutations were identified from 53 samples without IHC data. Thirty-seven percent of the identified mutations were large deletions encompassing one or more exons. In 27 patients whose tumors showed absence of either another protein or combination of proteins, no pathogenic mutations were identified. We conclude that modified long-range PCR can be used to preferentially amplify the PMS2 gene and avoid pseudogene interference, thus providing a clinically useful germline analysis of PMS2. Our data also support the use of IHC screening to direct germline testing of PMS2., ((c) 2010 Wiley-Liss, Inc.)

Background and Aims: Estimates have been made concerning the fraction of colorectal cancer (CRC) cases that meet Amsterdam I criteria but not Amsterdam II criteria. The aim of this study was to determine in a population setting what fraction of CRC cases can be considered familial high-risk, what fraction of these meet Amsterdam I or II criteria, and what fraction of CRC cases overall meet Amsterdam I and II criteria., Methods: The Utah Population Data Base (UPDB), which links Utah genealogies to the Utah Cancer Registry, was used to examine the aims of the study. Familial high-risk was operationally defined as CRC occurring at an age <50 years or as a part of a first-degree relative pair. A subset of Amsterdam positive cancers was tested for microsatellite instability (MSI) to determine what fraction of Amsterdam families was likely to have hereditary nonpolyposis colorectal cancer (HNPCC)., Results: Of the 6,628 CRC cases in the UPDB, 24.5% met the criteria for familial high-risk. Of these, 2.6% met Amsterdam I criteria and 5.5% Amsterdam II. Of total data base CRC cases, 0.8% met Amsterdam I criteria and 2.3% Amsterdam II. In a subset of colon tumors from Amsterdam families, 70% were MSI stable., Conclusions: Although nearly 25% of CRC cases in our population data base met a simple definition of familial high-risk, only a small fraction of these and a smaller fraction of total CRC cases met Amsterdam I or II criteria. Less than half of a limited set of tumors from Amsterdam families were MSI positive.

Background & Aims: Estimates of the frequency of hereditary nonpolyposis colon cancer (HNPCC) based on clinical criteria have varied widely. Recent studies of germline mismatch repair gene mutations have suggested that HNPCC accounts for close to 3% of all colon cancer, but this estimate may have been inflated by inclusion of founder effects peculiar to Finland. We therefore determined by genetic criteria the colon cancer burden associated with HNPCC in a population-based study of 1066 individuals from Utah and California., Methods: The coding regions of mismatch repair genes hMSH2 and hMLH1 were sequenced from the germline of those individuals whose tumors exhibited microsatellite instability., Results: Microsatellite instability was present in 16% (171/1066) of tumors. Pathogenic germline mismatch repair gene mutations were identified in 7 individuals, and missense amino acid changes of uncertain significance were identified in another 6 individuals. After adjusting for the availability of sufficient germline DNA for sequencing, the 7 clearly pathogenic mutations accounted for 0.86% of colon cancer at the population level. Individuals with these mutations were significantly younger, more likely to have a family history of colon and endometrial cancer, and more likely to have first-degree relatives with a young-age onset of colon cancer than individuals with unstable tumors but without germline mutations (P < 0.01)., Conclusions: We conclude that genetically defined HNPCC accounts for a very small percentage of colon cancer at the population level, a percentage less than that estimated by most previous clinical studies.