Germline Mutations In Mismatch Repair Genes Research Articles

Abstract LB-439: Distinct tumorigenic pathways within the hereditary nonpolyposis colorectal cancer

Abstract Background Identification of families with hereditary nonpolyposis colorectal cancer (HNPCC) allows for surveillance that has been proved to reduce morbidity and mortality from colorectal cancer (CRC). The HNPCC subset can broadly be divided into tumors caused by germline mismatch-repair (MMR) gene mutations, referred to as Lynch syndrome (LS), and those with an undefined genetic background, designated as familial colorectal cancer type X (FCC-X). Recognition of FCC-X tumor is challenging due to the lack of MMR defect and limited information is available about the global gene expression patterns in FCC-X tumors. We aimed at comprehensive pathway mapping of the global gene expression profile in FCC-X tumors with comparison to LS and sporadic CRC as controls. Materials and methods Tumour specimens were obtained from the national Danish HNPCC Register. RNA was extracted from 3-5 10-µm sections using the High Pure RNA Paraffin Kit (Roche, Castle Hill, Australia). The Whole-genome cDNA-mediated annealing selection extension and ligation (DASL) assay (Illumina, San Diego, CA) containing >24,000 probes in >18,000 genes was used for whole genome expression analysis. Expression values were analysed using the GenomeStudio software (Illumina, San Diego, CA) and imported into MeV 4.6.02. Canonical pathways were identified using DAVID Bioinformatics Resources 6.7. Results RNA was obtained from 180 tumors (60 LS, 60 FCC-X, 30 sporadic MSI-CRC and 30 sporadic MSS-CRC. Samples with <7000 genes represented (n=48) were excluded. Expression data from the remaining 132 samples were cubic normalized and a presence filter of 80% was applied (detection p-values ≤0.01). Sequence Alignment and Modeling (SAM) system analysis identified 3873 genes that differed significantly between LS/sporadic MSI-CRC and FCC-X/sporadic MSS-CRC. Using DAVID Bioinformatics resources, we identified 5 significantly up-regulated pathways in FCC-X/MSS-CRC including vascular smooth muscle contraction, G-protein coupled receptor signaling, calcium signaling, Wnt signalling and integrin cell surface interactions. For LS/MSI-CRC, we also identified 5 up-regulated pathways related antigen processing and presentation, DNA replication, cell cycle progression, and telomere maintenance. Conclusions Gene expression profiling using the DASL technology from 132 CRC identified MSI status as the major discriminator. Our data indicates that vascular smooth muscle contraction, G-protein coupled receptor signaling, calcium signaling, Wnt signaling, and integrin cell surface interactions pathways are up-regulated in FCC-X and MSS-CRC. These data provide strong evidence that these pathways play a role in development of CRC in these families and FCC-X should be considered as different clinical entity. These data also identify key signaling pathways as potential therapeutic targets in FCC- X tumors. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr LB-439. doi:1538-7445.AM2012-LB-439

Microsatellite Instability and DNA Mismatch Repair Protein Deficiency in Lynch Syndrome Colorectal Polyps

Colorectal cancers associated with Lynch syndrome are characterized by deficient DNA mismatch repair (MMR) function. Our aim was to evaluate the prevalence of microsatellite instability (MSI) and loss of MMR protein expression in Lynch syndrome-associated polyps. Sixty-two colorectal polyps--37 adenomatous polyps, 23 hyperplastic polyps, and 2 sessile serrated polyps (SSP)--from 34 subjects with germline MMR gene mutations were tested for MSI using a single pentaplex PCR for five mononucleotide repeat microsatellite markers, and also for expression of MLH1, MSH2, MSH6, and PMS2 proteins by immunohistochemistry. High-level MSI (MSI-H) was seen in 15 of 37 (41%) adenomatous polyps, one of 23 (4%) hyperplastic polyps, and one of two (50%) SSPs. Loss of MMR protein expression was seen in 18 of 36 (50%) adenomatous polyps, zero of 21 hyperplastic polyps, and zero of two SSPs. Adenomatous polyps 8 mm or larger in size were significantly more likely to show MSI-H [OR, 9.98; 95% confidence interval (CI), 1.52-65.65; P = 0.02] and deficient MMR protein expression (OR, 3.17; 95% CI, 1.20-8.37; P = 0.02) compared with those less than 8 mm in size. All (six of six) adenomatous polyps 10 mm or larger in size showed both MSI-H and loss of MMR protein expression by immunohistochemistry. Our finding that the prevalence of MMR deficiency increases with the size of adenomatous polyps suggests that loss of MMR function is a late event in Lynch syndrome-associated colorectal neoplasia. Although testing large adenomatous polyps may be of value in the diagnostic evaluation of patients with suspected Lynch syndrome, the absence of an MMR-deficient phenotype in an adenoma cannot be considered as a strong evidence against Lynch syndrome, as it is with colorectal carcinomas.

Molecular Pathways: Microsatellite Instability in Colorectal Cancer: Prognostic, Predictive, and Therapeutic Implications

Microsatellite instability (MSI) is the molecular fingerprint of the deficient mismatch repair (MMR) system, which characterizes ∼15% of colorectal cancers. MSI develops as a result of germline mutations in MMR genes or, more commonly, from epigenetic silencing of MLH1 in sporadic tumors occurring in a background of methylation of CpG islands in gene promoter regions and in tumors that frequently show hotspot mutations in the BRAF oncogene. MSI tumors have distinct phenotypic features and have been consistently associated with a better stage-adjusted prognosis compared with microsatellite stable tumors. MSI negatively predicts response to 5-fluorouracil and may also determine responsiveness to other drugs used for treatment of colorectal cancers. Recent data have expanded the molecular heterogeneity of MSI tumors and may contribute to our understanding of differential chemosensitivity. The ability to identify deficient MMR has important implications for patient management, and it holds promise for therapeutic exploitation and for the development of novel therapeutics.

Comparison of the clinical prediction model PREMM1,2,6 and molecular testing for the systematic identification of Lynch syndrome in colorectal cancer

BackgroundLynch 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.ObjectiveTo compare...

C-Terminal Fluorescent Labeling Impairs Functionality of DNA Mismatch Repair Proteins

The human DNA mismatch repair (MMR) process is crucial to maintain the integrity of the genome and requires many different proteins which interact perfectly and coordinated. Germline mutations in MMR genes are responsible for the development of the hereditary form of colorectal cancer called Lynch syndrome. Various mutations mainly in two MMR proteins, MLH1 and MSH2, have been identified so far, whereas 55% are detected within MLH1, the essential component of the heterodimer MutLα (MLH1 and PMS2). Most of those MLH1 variants are pathogenic but the relevance of missense mutations often remains unclear. Many different recombinant systems are applied to filter out disease-associated proteins whereby fluorescent tagged proteins are frequently used. However, dye labeling might have deleterious effects on MutLα's functionality. Therefore, we analyzed the consequences of N- and C-terminal fluorescent labeling on expression level, cellular localization and MMR activity of MutLα. Besides significant influence of GFP- or Red-fusion on protein expression we detected incorrect shuttling of single expressed C-terminal GFP-tagged PMS2 into the nucleus and found that C-terminal dye labeling impaired MMR function of MutLα. In contrast, N-terminal tagged MutLαs retained correct functionality and can be recommended both for the analysis of cellular localization and MMR efficiency.

Identification of Cancer Patients with Lynch Syndrome: Clinically Significant Discordances and Problems in Tissue-Based Mismatch Repair Testing

Tissue-based microsatellite instability (MSI) analysis and immunohistochemistry for DNA mismatch repair proteins are accepted screening tools to evaluate patients with cancer for Lynch syndrome. These laboratory analyses are thus important tools in cancer prevention. Quality assurance review was conducted to identify test discordances and problems. These results were then analyzed in conjunction with genetic testing outcomes. Six hundred and forty-six consecutive tumors from 2002 to 2010 were examined. MSI-low tumors were excluded so that 591 tumors comprised the final analyses. Discordance was defined as a discrepancy between immunohistochemical and MSI analysis. Problem was defined as indeterminate or questionable immunohistochemical or MSI results. All results and clinical and family histories were centrally reviewed by two pathologists and one genetics counselor. Discordances and problems were identified in 23 of 591 (3.9%) of the tumors. Twelve of 102 MSI-high carcinomas (11.8%) and one of 489 microsatellite stable tumors had discordant immunohistochemistry. Of these 13 tumors, 11 were from patients who had personal and/or family cancer histories concerning for a germline mismatch repair gene mutation. In addition to discordances, 10 tumors with problematic immunohistochemical profiles were identified. Accurate evaluation of MSI was possible in all tumors. In summary, concordance between immunohistochemistry and MSI was high, particularly for tumors that are microsatellite stable. Greater frequency of test discordance was identified in the tumors that were MSI-high. Thus, a major consequence of the use of immunohistochemistry by itself as a screen is the failure to identify colorectal and endometrial cancer patients who likely have Lynch syndrome.

Relevance, Pathogenesis, and Testing Algorithm for Mismatch Repair–Defective Colorectal Carcinomas: A Report of the Association for Molecular Pathology

Loss-of-function defects in DNA mismatch repair (MMR), which manifest as high levels of microsatellite instability (MSI), occur in approximately 15% of all colorectal carcinomas (CRCs). This molecular subset of CRC characterizes patients with better stage-specific prognoses who experience no benefit from 5-fluorouracil chemotherapy. Most MMR-deficient (dMMR) CRCs are sporadic, but 15% to 20% are due to inherited predisposition (Lynch syndrome). High penetrance of CRCs in germline MMR gene mutation carriers emphasizes the importance of accurate diagnosis of Lynch syndrome carriers. Family-based (Amsterdam), patient/family-based (Bethesda), morphology-based, microsatellite-based, and IHC-based screening criteria do not individually detect all germline mutation carriers. These limitations support the use of multiple concurrent tests and the screening of all patients with newly diagnosed CRC. This approach is resource intensive but would increase detection of inherited and de novo germline mutations to guide family screening. Although CRC prognosis and prediction of 5-fluorouracil response are similar in both the Lynch and sporadic dMMR subgroups, these subgroups differ significantly with regard to the implications for family members. We recommend that new CRCs should be classified into sporadic MMR-proficient, sporadic dMMR, or Lynch dMMR subgroups. The concurrent use of MSI testing, MMR protein IHC, and BRAF c.1799T>A mutation analysis would detect almost all dMMR CRCs, would classify 94% of all new CRCs into these MMR subgroups, and would guide secondary molecular testing of the remainder.

Prognostic and Predictive Impact of DNA Mismatch Repair in the Management of Colorectal Cancer

Colorectal cancers develop via two major pathways that include chromosomal instability and microsatellite instability. Microsatellite instability occurs due to deficient DNA mismatch repair (MMR), which can be caused by epigenetic silencing of the MLH1 MMR gene in sporadic colorectal cancers or germline mutations in MMR genes that result in Lynch syndrome. While the molecular origin of deficient MMR differs, sporadic and Lynch syndrome tumors share similar pathological features and have a more favorable stage-adjusted prognosis compared with MMR-proficient cases. While controversy remains, there is evidence to suggest that deficient MMR may predict a lack of benefit from 5-fluorouracil-based adjuvant chemotherapy. The focus of this article is on the MMR phenotype and its prognostic and predictive implications for the management of patients with colorectal cancer.

Ovarian cancer linked to lynch syndrome typically presents as early-onset, non-serous epithelial tumors

Objective Heredity is a major cause of ovarian cancer and during recent years the contribution from germline mismatch repair (MMR) gene mutations linked to Lynch syndrome has gradually been recognized. Methods We characterized clinical features, tumor morphology and mismatch repair defects in all ovarian cancers identified in Swedish and Danish Lynch syndrome families. Results In total, 63 epithelial ovarian cancers developed at mean 48 (range 30–79) years of age with 47% being early stage (FIGO stage I). Histologically, endometrioid (35%) and clear cell (17%) tumors were overrepresented. The underlying MMR gene mutations in these families affected MSH2 in 49%, MSH6 in 33% and MLH1 in 17%. Immunohistochemical loss of the corresponding MMR protein was demonstrated in 33/36 (92%) tumors analyzed. Conclusion The combined data from our cohorts demonstrate that ovarian cancer associated with Lynch syndrome typically presents at young age as early-stage, non-serous tumors, which implicates that a family history of colorectal and endometrial cancer should be specifically considered in such cases.

Utility of immunohistochemistry in detecting alterations of mismatch repair genes of DNA. A series of 48 cases of colorectal cancer

Hereditary non-polyposis colorectal cancer (HNPCC) is associated in more than 95% to a germline mutation in the genes of the mismatch repair (MMR) of DNA. The aim of this study was to assess the utility of immunohistochemistry, a simple and fast technique, in the triage of families where HNPCC is suspected. Tumor samples included in this study were from patients with resection for colorectal cancer, examined in our laboratory between 2004 and 2007. For each case, a formalin-fixed paraffin-embedded tissue block containing tumor tissue and normal adjacent mucosa was selected. Tumor specimens were examined with immunohistochemistry for the presence of hMLH1, hMSH2, and hMSH6 proteins. Scoring of the tumor staining was performed without any knowledge of patients' family history. The loss of protein expression was noted in four patients among 48cases tested: two cases with isolated loss of hMSH2, a case with isolated loss of hMSH6 and one case with combined loss of MSH2/MSH6. No case has shown a suppression of hMLH1 protein. Comparing the immunohistochemical results for clinical has revealed a clear correlation between loss of protein expression demonstrated by immunohistochemistry and clinical data. Indeed, three cases among the four who showed no expression of MMR proteins showed at least one clinical criterion predictive of HNPCC. In conclusion, our study support the potential utility of immunohistochemistry to identify a significant portion of colorectal tumors derived from germline mutation of MMR genes and can be used as an adjunct measure in the identification of HNPCC.

Genetic profiles of hereditary nonpolyposis colorectal cancer.

469 Background: With the aim to identify genetic markers of hereditary nonpolyposis colorectal cancer (HNPCC), we applied tiling BAC array-based comparative genomic hybridization (aCGH) to 46 HNPCC-associated colorectal cancer. Methods: 32 k iling BAC arrays were used to generate high-density genomic profiles. Tumors were selected through a case-control design with half of the tumors derived from individuals with disease-predisposing mismatch repair gene mutations and the reminder from phenotypic HNPCC families without identified mutations. In addition, an equal number of sporadic tumors were used for comparison. Results: Tumors with disease-predisposing germline mutations showed frequent gains of chromosomes 1p (39%), 17 (43%), 19 (57%) and 22q (30%). HNPCC associated tumors without mutations did as a group have more complex alterations with the most frequent changes being gains of 20q (70%), 19 (35%), 17 (26%) and loss of 18 (39%). Gains of 1p and 20q and loss of chromosome 18 were identified as significant discriminators between HNPCC tumors with/without germline MMR gene mutations. Conclusions: The aCGH profiles of HNPCC-associated colorectal cancer suggest that specific gains and losses may be used to distinguish between tumors with/without germline mismatch repair gene mutations. No significant financial relationships to disclose.

Atypical identification of Lynch syndrome by immunohistochemistry and microsatellite instability analysis on jejunal adenocarcinoma

Background Lynch syndrome (LS) is a hereditary cancer condition associated with germline mutations in the mismatch repair genes MLH1, MSH2, MSH6 and PMS2. This condition has been traditionally described in terms of an increased risk for early-onset colorectal and endometrial cancers. Individuals with LS additionally have an increased risk to develop other cancers including ovarian, gastric, urinary tract, hepatobiliary tract, small bowel, brain, and skin cancers. The preferred method of genetic testing for LS is to initially perform microsatellite instability (MSI) analysis and/or immunohistochemistry (IHC) staining as a test on the tumor tissue of an affected individual. If abnormal, this testing would indicate that a germline mismatch repair gene mutation is more likely to explain the cancer and, if IHC is performed, may also indicate which gene to test first via molecular analysis. MSI/IHC has been more widely validated for colon and endometrial cancers as opposed to other cancers associated with this condition.

Lynch Syndrome - is breast cancer a feature?

Background The debate on whether or not breast cancer is in the tumor spectrum for Lynch syndrome produces a conundrum for healthcare providers. The classic tumor spectrum for Lynch Syndrome (LS) includes colon, endometrial, ovarian, stomach, small intestine, hepatobiliary, urinary tract and brain/central nervous system cancers. Muir-Torre Syndrome (MTS) is a variant of LS that is associated with additional skin lesions including sebaceous gland tumors and keratoacanthomas. MTS was observed in 28% of LS families when assessing for MTS skin lesions [1]. It has also been reported that 10-14% of individuals with MTS present initially with breast cancer [2,3]. An extensive study published in 2002 excluded breast cancer as part of the tumor spectrum associated with LS [4]. However, more recently it was reported that DNA mismatch repair (MMR) gene deficiencies were identified in 51% of breast cancers arising in MMR mutation carriers [5]. Another study reported a male with an MLH1 mutation who had both colon and breast cancer. The breast cancer exhibited somatic reduction to homozygosity for the MLH1 mutation [6]. Here we report two unrelated families in which the proband has a germline MMR gene mutation and bilateral breast cancer, and one family in which the proband had ovarian and renal cancer and her daughter, maternal aunt and cousin had breast cancer at age 47, 59, and 48 respectively. This raises the question are these breast cancers associated with the MMR mutations or a breast cancer susceptibility gene and what testing should be offered?

The Spindle-Assembly Checkpoint, Aneuploidy, and Gastrointestinal Cancer

Genomic instability is a common occurrence in solid tumors, and it has long been conjectured that this process plays a causal role in cancer. The field of human molecular genetics has provided a means to test this hypothesis, fueled in part by the analysis of hereditary cancer-predisposition syndromes. Some of the first unequivocal support for the idea came from the discovery in 1993 that hereditary nonpolyposis colon cancer is caused by germline mutations of mismatch-repair genes.1,2 Work on the autosomal dominant hereditary breast and ovarian cancer predisposition syndromes, as well as on rare autosomal recessive syndromes such as Fanconi's . . .

The role of SMAD4 in early‐onset colorectal cancer

Chromosomal loss within the region of 18q and loss of SMAD4 expression have been reported to be frequent somatic events during colorectal cancer tumour progression; however, their associations with age at onset have not been widely studied. We analysed 109 tumours from a population-based case-family study based on colorectal cancers diagnosed before the age of 45 years. These patients with early-onset colorectal cancer had been previously screened for germ-line mismatch repair gene mutations, microsatellite instability (that included the mononucleotide repeat in TGFbetaRII) and somatic k-ras mutations. We measured SMAD4 protein expression using immunohistochemistry and SMAD4 copy number using quantitative real-time PCR. Loss of SMAD4 protein expression was observed in 27/109 (25%) of cancers tested and was more commonly observed in rectal tumours (15/41, 36%) when compared with tumours arising in the colon (11/66, 17%) (P = 0.04). There was no association between SMAD4 protein expression and TGFbetaR11 mutation status, SMAD4 copy number, family history, MSI status, tumour stage or grade. Loss of SMAD4 expression is a common feature of early-onset colorectal tumours as it is in colorectal cancers diagnosed in other age-groups. Taken together, the molecular pathways (genetic and epigenetic) now known to be involved in early-onset colorectal cancer only explain a small proportion of the disease and require further exploration.

Aberrant DNA Methylation in Hereditary Nonpolyposis Colorectal Cancer Without Mismatch Repair Deficiency

Approximately half of the families that fulfill Amsterdam criteria for Lynch syndrome or hereditary nonpolyposis colorectal cancer (HNPCC) do not have evidence of the germline mismatch repair gene mutations that define this syndrome and result in microsatellite instability (MSI). The carcinogenic pathways and the best diagnostic approaches to detect microsatellite stable (MSS) HNPCC tumors are unclear. We investigated the contribution of epigenetic alterations to the development of MSS HNPCC tumors. Colorectal cancers were divided into 4 groups: (1) microsatellite stable, Amsterdam-positive (MSS HNPCC) (N = 22); (2) Lynch syndrome cancers (identified mismatch repair mutations) (N = 21); (3) sporadic MSS (N = 92); and (4) sporadic MSI (N = 46). Methylation status was evaluated for CACNAG1, SOCS1, RUNX3, NEUROG1, MLH1, and long interspersed nucleotide element-1 (LINE-1). KRAS and BRAF mutation status was analyzed. MSS HNPCC tumors displayed a significantly lower degree of LINE-1 methylation, a marker for global methylation, than any other group. Although most MSS HNPCC tumors had some degree of CpG island methylation, none presented a high index of methylation. MSS HNPCC tumors had KRAS mutations exclusively in codon 12, but none harbored V600E BRAF mutations. Tumors from Amsterdam-positive patients without mismatch repair deficiency (MSS HNPCC) have certain molecular features, including global hypomethylation, that distinguish them from all other colorectal cancers. These characteristics could have an important impact on tumor behavior or treatment response. Studies are underway to further assess the cause and effects of these features.

Risk of Pancreatic Cancer in Families With Lynch Syndrome

Lynch syndrome is an inherited cause of colorectal cancer caused by mutations of DNA mismatch repair (MMR) genes. A number of extracolonic tumors have been associated with the disorder, including pancreatic cancer; however, the risk of pancreatic cancer in Lynch syndrome is uncertain and not quantified. To estimate pancreatic cancer risk in families with germline MMR gene mutations. Cancer histories of probands and their relatives were evaluated in MMR gene mutation carriers in the familial cancer registries of the Dana-Farber Cancer Institute (n = 80), Boston, Massachusetts, and University of Michigan Comprehensive Cancer Center (n = 67), Ann Arbor, Michigan. Families enrolled before the study start date (June 2008) were eligible. Age-specific cumulative risks and hazard ratio estimates of pancreatic cancer risk were calculated and compared with the general population using modified segregation analysis, with correction for ascertainment. Age-specific cumulative risks and hazard ratio estimates of pancreatic cancer risk. Data on 6342 individuals from 147 families with MMR gene mutations were analyzed. Thirty-one families (21.1%) reported at least 1 case of pancreatic cancer. Forty-seven pancreatic cancers were reported (21 men and 26 women), with no sex-related difference in age of diagnosis (51.5 vs 56.5 years for men and women, respectively). The cumulative risk of pancreatic cancer in these families with gene mutations was 1.31% (95% confidence interval [CI], 0.31%-2.32%) up to age 50 years and 3.68% (95% CI, 1.45%-5.88%) up to age 70 years, which represents an 8.6-fold increase (95% CI, 4.7-15.7) compared with the general population. Among 147 families with germline MMR gene mutations, the risk of pancreatic cancer was increased compared with the US population. Individuals with MMR gene mutations and a family history of pancreatic cancer are appropriate to include in studies to further define the risk of premalignant and malignant pancreatic neoplasms and potential benefits and limitations of surveillance.

Establishing pathogenicity of germline mismatch repair gene mutations: A Bayesian model

An increasing problem in diagnostic molecular genetics is establishing the pathogenicity of mutations. It is therefore fortunate that in Lynch Syndrome data from the analysis of tumours can provide evidence for or against pathogenicity. Testing tumours for microsatellite instability and immunohistochemical changes in protein expression is now in almost routine use, but how confident can one be that these findings are evidence for or against pathogenicity? Attempts are being made to address the general issue of interpretation through e.g.

Mononucleotide precedes dinucleotide repeat instability during colorectal tumour development in Lynch syndrome patients

A progressive accumulation of genetic alterations underlies the adenoma-carcinoma sequence of colorectal cancer. This accumulation of mutations is driven by genetic instability, of which there are different types. Microsatellite instability (MSI) is the predominant type present in the tumours of Lynch syndrome patients and in a subset of sporadic tumours. It is generally accepted that MSI can be found in the early stages of tumour progression, such as adenomas; however, the frequencies reported vary widely among studies. Moreover, data on the qualitative differences between adenomas and carcinomas, or between tumours of hereditary and sporadic origin, are scarce. We compared MSI in samples of colorectal adenoma and colorectal carcinoma in order to identify possible differences along the adenoma-carcinoma sequence. We compared germline mismatch repair (MMR) gene mutation carriers and non-carriers, to address possible differences of instability patterns between Lynch syndrome patients and patients with sporadic tumours. We found a comparable relative frequency of mono- and dinucleotide instability in sporadic colorectal adenomas and carcinomas, dinucleotide instability being observed most frequently in these sporadic tumours. In MMR gene truncating mutation carriers, the profile was different: colorectal adenomas showed predominantly mononucleotide instability and in colorectal carcinomas, also more mononucleotide than dinucleotide instability was detected. We conclude that MSI profiles differ between sporadic and Lynch syndrome tumours, and that mononucleotide marker instability precedes dinucleotide marker instability during colorectal tumour development in Lynch syndrome patients. As mononucleotide MSI proves to be highly sensitive for detecting mutation carriers, we propose the use of mononucleotide markers for the identification of possible Lynch syndrome patients.

Deficient DNA Mismatch Repair Is Common in Lynch Syndrome-Associated Colorectal Adenomas

Lynch syndrome is caused by germline mutations in DNA mismatch repair (MMR) genes. Both microsatellite instability (MSI) testing and immunohistochemical analyses (IHC) of colon cancers are valuable diagnostic strategies for Lynch syndrome. We sought to determine whether these markers of MMR deficiency were also detectable in pre-cancerous colorectal adenomas. Fifteen subjects with a germline MMR gene mutation who had 44 adenomas removed during surveillance colonoscopy were identified. MSI testing and IHC for MLH1, MSH2, and MSH6 were performed. MSI was detected in 23 adenomas. There was a significant association between MSI and high-grade dysplasia (P = 0.006) and distal location (P = 0.0008). Loss of MMR protein by IHC was detected in 31 adenomas. A significant association was observed between loss of staining by IHC and high-grade dysplasia (P = 0.04). Among the 40 adenomas in which both MSI tests and IHC were performed, the presence of a germline mutation correlated with an abnormal MSI result in 58% of cases, an abnormal IHC result in 70% of cases, and either an abnormal MSI or IHC result in 73% of cases. The combination of MSI and IHC testing in colorectal adenomas is a sensitive screen for the detection of Lynch syndrome and may be particularly useful when Lynch syndrome is suspected and adenomatous polyps are the only tissues available for analysis.