MLH1 Hypermethylation Research Articles

Promoter hypermethylation of DNA repair genes MLH1 and MSH2 in adenocarcinomas and squamous cell carcinomas of the lung

Promoter hypermethylation of DNA repair genes MLH1 and MSH2 in adenocarcinomas and squamous cell carcinomas of the lung

Promoter hypermethylation of DNA repair genes MLH1 and MSH2 in adenocarcinomas and squamous cell carcinomas of the lung

Five years survival of lung cancer is 16%, significantly lower than in prostate (99.9%), breast (88.5%) and colon (64.1%) carcinomas. When diagnosed in the surgical stage it increases to 50% but this group only comprises 14–16% of the cases. DNA methylation has emerged as a potential cancer-specific biomarker. Hypermethylation of CpG islands located in the promoter regions of tumour suppressor genes is now firmly established as an important mechanism for gene inactivation.This retrospective study included 40 squamous cell carcinomas and 40 adenocarcinomas in various surgical TNM stages to define methylation profile and possible silencing of DNA repair genes – MLH1 and MSH2 – using Methylation-Specific PCR and protein expression by immunohistochemistry in tumoural tissue, preneoplastic lesions and respiratory epithelium with normal histological features.The protein expression of MLH1 and MSH2 genes, in the available preneoplastic lesions and in normal cylindrical respiratory epithelium appeared reduced. The frequency of promoter hypermethylation found on these DNA repair genes was elevated, with a higher prevalence of methylation of MLH1 gene in 72% of squamous cell carcinoma. The differences are not so obvious for MSH2 promoter hypermethylation. No correlation was found among the status of methylation, the protein expression and the clinicopathological characteristics.With a larger study, a better characterization of the hypermethylation status of neoplastic and preneoplastic lesions in small biopsies would be achieved, inherent to tumour histology, heterogeneity and preservation, and finally differences in the study population to elucidate other possible mechanisms of altered expression of the hMLH1 and hMSH.

Abstract C52: A phase Ib biomarker trial of naproxen in patients at risk for DNA mismatch repair deficient colorectal cancer

Abstract Rationale: Approximately 15% of colorectal cancers (CRC) display Microsatellite Instability (MSI). The DNA mismatch repair (MMR) system is deficient in this tumor subtype secondary to a germline mutation in one of the MMR system genes (MLH1, MSH2, MSH6, PMS2) or to the presence of hypermethylation MLH1. Therefore, MSI tumors can have a genetic origin (Lynch syndrome) or a sporadic origin (hypermethylated MSI tumors). Patients and families diagnosed with Lynch Syndrome have an up to 70-80% lifetime risk of CRC. Therefore, this high-risk population may benefit from effective chemopreventive strategies. Results from the CAPP-II trial suggest that aspirin use is associated with reduction of risk for CRC and other tumors in Lynch syndrome; however the large doses needed and potential side effects present barriers to adoption. Other non-steroidal anti-inflammatory drugs (NSAID) with stronger efficacy and better tolerability may be reasonable alternatives for CRC chemoprevention. Naproxen is a NSAID that is widely used in the community with an excellent safety profile. Recent pre-clinical data sponsored by the Division of Cancer Prevention of the National Cancer Institute using a conditional mouse model of Lynch Syndrome (VC-MSH2-LoxP) have shown that Naproxen is the most effective agent from a panel of NSAIDs preventing CRC. Therefore, this clinical trial was designed to confirm the activity of Naproxen observed in vivo in patients diagnosed with Lynch Syndrome. Because NSAIDs exert their therapeutic effects through the inhibition of COX-1/-2 which in turn leads to a reduction in prostaglandin production, tissue level of prostaglandin E2 (PGE2) is a robust biomarker for the effect of NSAIDs. We wish to report herein the background and schema of this early-phase (Ib) cancer prevention trial to introduce the concept of NSAID chemoprevention strategy in this specialized and genetically well-defined patient population, and thus to also facilitate the identification of additional collaborators for potential further larger trials initiatives. Design: Eligible patients include individuals harboring a pathogenic mutation in one of the MMR genes and individuals who have been diagnosed with non-sporadic MSI-high tumors (i.e. no evidence of MLH1 hypermethylation or BRAF mutation). The primary endpoints are to test whether Naproxen at a once-daily 220 mg (low-) or 440 mg (high-) dose, administered for 6 months, reduces the concentration of PGE2 levels in normal colorectal mucosa, when compared to placebo; and to determine the safety profile and tolerability of Naproxen. A total of 60 participants will be randomized to achieve an evaluable sample size of 45 participants. Under the assumption of an effect size of 1.25, we will have 80% power for pairwise comparisons by the two-sample t-test among the three groups with 15 evaluable participants per group. Response to treatment will be defined as having a 30% reduction in the PGE2 level post-treatment. Secondary endpoints include the determination of Naproxen concentrations in plasma and in normal colorectal mucosa after 6 months of treatment, and levels of PGE2 in urine after 6 months of treatment, all measured by validated biomarker assays. The study will be conducted at three clinical sites (The University of Texas MD Anderson Cancer Center, The University of Michigan Comprehensive Cancer Center and Dana Farber Cancer Institute). Screening and accrual are expected to begin in the latter part of 2013. Supported by NCI, DCP Contract HHSN261201200034I to the UT MD Anderson Cancer Prevention Agent Development Program: Early Phase Clinical Research Consortium. Citation Format: Eduardo Vilar, Y. Nancy You, Lana A. Vornik, Elena M. Stoffel, Ramona M. Lim, Steven M. Lipkin, Marjorie Perloff, Powel H. Brown. A phase Ib biomarker trial of naproxen in patients at risk for DNA mismatch repair deficient colorectal cancer. [abstract]. In: Proceedings of the Twelfth Annual AACR International Conference on Frontiers in Cancer Prevention Research; 2013 Oct 27-30; National Harbor, MD. Philadelphia (PA): AACR; Can Prev Res 2013;6(11 Suppl): Abstract nr C52.

Prospective correlation between clinical and pathologic criteria identification of Lynch syndrome (LS) in endometrial carcinoma (EC) patients and relapse.

1543 Background: Prospective comparison of different methods for recognition of LS associated EC is lacking. Microsatellite instability (MSI) has been observed to be inconsistent as a prognostic factor in EC. The aim of this study was to analyze the impact of MSI and Mismatch Repair (MMR)-deficiency on LS identification and prognosis in a prospective series of EC treated in one single institution. Methods: Consecutive and prospective EC patients were included. Clinical data, family history of cancer and criteria for LS were evaluated. MSI and MMR protein expression were performed. When loss of MMR proteins and/or high MSI (MSI-H) was observed, complete sequencing and large genomic rearrangement analysis of germline MLH1, MSH2, MSH6 or PMS2 was done once MLH1 methylation was excluded. Results: Seventy-seven women diagnosed with EC were enrolled from 2009 to 2012 with a median age of 62 (31-87), 84% histological type I, 16% type II and FIGO stages I 83%, II 2.8%, III-IVA 7% and IVB 7%. Among which, 6.6% fulfilled revised Bethesda criteria (rBC), 5.3% criteria defined by the Society Gynecologic Oncology (>20%-to-25% risk of LS) (SGO) and 5.3% Amsterdam II criteria (AII). Seventy-four underwent surgery with curative-intent. Tumor tissue was unavailable in 5 cases for molecular analysis. MSI-H was observed in16 cases (22%) and 18 (24%) had loss of expression of MLH1 (14), MSH2 (2), MSH6 (1) or PMS2 (1). Nine MLH1 hypermethylation, 10 K-RAS and no BRAF mutations were identified. Four (5.5%) pathogenic MMR germline mutations were recognized: 2 MSH2, one MSH6 and one PMS2. One patient (25%) with MSH6 mutation did not fulfil rBC, SGO nor AII criteria and was identified both by MSI-H and loss of MSH6 expression. Median follow-up was 23.4 (0.2-76.3) months. No correlation between MSI-H, MMR gene mutation and relapse was observed in stage I-IVA EC. Conclusions: Based on these results, rBC, AII and SGO criteria for identification of LS in EC do not identify 25% of germline MMR gene mutations. No correlation with relapse and MSI-H could be identified.

LINE-1 Hypomethylation Is Associated With a Poor Prognosis Among Patients With Curatively Resected Esophageal Squamous Cell Carcinoma

To investigate the relationship between the long interspersed nucleotide element-1 (L1/LINE-1) methylation level and the disease-free survival and cancer-specific survival in patients with esophageal squamous cell carcinoma (ESCC). Cancer cells exhibit 2 types of deoxyribonucleic acid (DNA) methylation alterations: global DNA hypomethylation and site-specific CpG island promoter hypermethylation. Global DNA hypomethylation plays a role in genomic instability and carcinogenesis. DNA methylation in the LINE-1 repetitive element is a good indicator of the global DNA methylation level. Although the LINE-1 methylation level is attracting interest as a useful marker for predicting cancer prognosis, the prognostic significance of LINE-1 hypomethylaiton in ESCC remains unclear. Using 217 curatively resected ESCC specimens, we quantified the LINE-1 methylation by utilizing the bisulfite pyrosequencing technology. Promoter methylation levels of MGMT and MLH1 were also evaluated by pyrosequencing. ESCC showed significantly lower LINE-1 methylation levels in comparison with matched normal esophageal mucosa (P < 0.0001; N = 50). LINE-1 hypomethylation was significantly associated with disease-free survival [log-rank P = 0.0008; univariate hazard ratio (HR): 2.32, 95% confidence interval (CI): 1.38-3.84, P = 0.0017; multivariate HR: 1.81, 95% CI: 1.06-3.05, P = 0.031] and cancer-specific survival (log-rank P = 0.0020; univariate HR: 2.21, 95% CI: 1.33-3.60, P = 0.0026; multivariate HR: 1.87, 95% CI: 1.12-3.08, P = 0.018]. MGMT and MLH1 hypermethylation were not associated with patient prognosis. LINE-1 hypomethylation in ESCC is associated with a shorter survival, thus suggesting that it has potential for use as a prognostic biomarker.

An Update on the Pathogenesis of Lynch Syndrome: Recently Described Novel Molecular Mechanisms

Lynch syndrome, originally described in 1913 and previously known as hereditary nonpolyposis colorectal carcinoma syndrome, is the most common hereditary cancer syndrome. This syndrome is classically due to germline mutations in the mismatch repair genes MLH1, MSH2, MSH6, or PMS2. The cancer risk for patients with Lynch syndrome is not limited to the colorectum; women with Lynch syndrome are at risk for endometrial cancer, and Lynch patients of both genders are at risk for other cancers as well. There are cases of cancers in families that meet the clinical criteria (Amsterdam and Bethesda criteria) for Lynch syndrome but do not have a mutation in the one of the four classic mismatch repair genes. For some time, there has been speculation that other mutations or mechanisms were responsible for a subset of Lynch syndrome patients; much research has gone into identifying those alternative mutations and mechanisms. Recently, EPCAM deletion, CHEK2 mutations, and germline MLH1 hypermethylation have been identified as alternative mutations that cause Lynch syndrome in mismatch repair-negative patients. This article reviews these novel mechanisms and mutations, their clinical significance, and the pathogenesis of these Lynch causing mutations.

MLH1 promoter hypermethylation in the analytical algorithm of Lynch syndrome: a cost-effectiveness study

The analytical algorithm of Lynch syndrome (LS) is increasingly complex. BRAF V600E mutation and MLH1 promoter hypermethylation have been proposed as a screening tool for the identification of LS. The aim of this study was to assess the clinical usefulness and cost-effectiveness of both somatic alterations to improve the yield of the diagnostic algorithm of LS. A total of 122 colorectal tumors from individuals with family history of colorectal cancer that showed microsatellite instability and/or loss of mismatch repair (MMR) protein expression were studied. MMR germline mutations were detected in 57 cases (40 MLH1, 15 MSH2 and 2 MSH6). BRAF V600E mutation was assessed by single-nucleotide primer extension. MLH1 promoter hypermethylation was assessed by methylation-specific multiplex ligation-dependent probe amplification in a subset of 71 cases with loss of MLH1 protein. A decision model was developed to estimate the incremental costs of alternative case-finding methods for detecting MLH1 mutation carriers. One-way sensitivity analysis was performed to assess robustness of estimations. Sensitivity of the absence of BRAF mutations for depiction of LS patients was 96% (23/24) and specificity was 28% (13/47). Specificity of MLH1 promoter hypermethylation for depiction of sporadic tumors was 66% (31/47) and sensitivity of 96% (23/24). The cost per additional mutation detected when using hypermethylation analysis was lower when compared with BRAF study and germinal MLH1 mutation study. Somatic hypermethylation of MLH1 is an accurate and cost-effective pre-screening method in the selection of patients that are candidates for MLH1 germline analysis when LS is suspected and MLH1 protein expression is absent.

Germline promoter hypermethylation of tumor suppressor genes in gastric cancer

To explore germline hypermethylation of the tumor suppressor genes MLH1, CDH1 and P16(INK4a) in suspected cases of hereditary gastric cancer (GC). A group of 140 Chinese GC patients in whom the primary cancer had developed before the age of 60 or who had a familial history of cancer were screened for germline hypermethylation of the MLH1, CDH1 and P16(INK4a) tumor suppressor genes. Genomic DNA was extracted from peripheral blood leukocytes and modified by sodium bisulfite. The treated DNA was then subjected to bisulfite DNA sequencing for a specific region of the MLH1 promoter. The methylation status of CDH1 or P16(INK4a) was assayed using methylation-specific PCR. Clonal bisulfite allelic sequencing in positive samples was performed to obtain a comprehensive analysis of the CpG island methylation status of these promoter regions. Methylation of the MLH1 gene promoter was detected in the peripheral blood DNA of only 1/140 (0.7%) of the GC patient group. However, this methylation pattern was mosaic rather than the allelic pattern which has previously been reported for MLH1 in hereditary non-polyposis colorectal cancer (HNPCC) patients. We found that 10% of the MLH1 alleles in the peripheral blood DNA of this patient were methylated, consistent with 20% of cells having one methylated allele. No germline promoter methylation of the CDH1 or P16(INK4a) genes was detected. Mosaic germline epimutation of the MLH1 gene is present in suspected hereditary GC patients in China but at a very low level. Germline epimutation of the CDH1 or P16(INK4a) gene is not a frequent event.

“Null Pattern” of Immunoreactivity in a Lynch Syndrome-Associated Colon Cancer Due to Germline MSH2 Mutation and Somatic MLH1 Hypermethylation

Lynch syndrome accounts for approximately 3% of newly diagnosed colorectal cancers and is caused by germline defects in DNA mismatch repair genes. Screening of patients for Lynch syndrome can be done by immunohistochemical staining for a panel of mismatch repair proteins and/or DNA testing for microsatellite instability. We describe a unique "null" immunophenotype in a Lynch syndrome associated colon cancer in a 71-year-old woman who also had a personal history of ureteral cancer and a strong family history of various malignancies. Immunohistochemical stains for MLH1, MSH2, PMS2, and MSH6 were completely negative in the tumor cells, with positive staining in stromal and inflammatory cells. Mutation analysis using peripheral blood showed a germline G587R mutation in the MSH2 gene. Further testing revealed the tumor to be positive for MLH1 promoter hypermethylation. Normal colonic mucosa adjacent to the tumor was negative for MLH1 promoter methylation. The lack of immunostaining for any of the 4 DNA mismatch repair proteins in this extremely unusual case was, therefore, related to a germline MSH2 mutation and somatic MLH1 promoter hypermethylation.

Molecular analysis of DNA repair gene methylation and protein expression during chemical-induced rat lung carcinogenesis

A defective ratio between DNA damage and repair may result in the occurrence of a malignant phenotype. Previous studies have found that many genetic alterations in DNA repair genes occur frequently in lung cancer. However, the epigenetic mechanisms underlying this tumorigenesis are not clear. Herein, we have used a chemical-induced rat lung carcinogenesis model to study the evolution of methylation alterations of DNA repair genes BRCA1, ERCC1, XRCC1, and MLH1. Methylation-specific PCR and immunohistochemistry were used to analyze gene methylation status and protein expression during the progression of lung carcinogenesis. Promoter hypermethylation of BRCA1 was only detected in three samples of infiltrating carcinoma. CpG island hypermethylation of ERCC1, XRCC1, and MLH1 was found to increase gradually throughout lung carcinogenesis progression. Both the prevalence of at least one methylated gene and the average number of methylated genes were heightened in squamous metaplasia and dysplasia compared with normal tissue and hyperplasia, and was further increased in carcinoma in situ (CIS) and infiltrating carcinoma. Immunohistochemical analysis showed that BRCA1 and MLH1 protein expression decreased progressively during the stages of lung carcinogenesis, whereas ERCC1 and XRCC1 expression were only found in later stages. Although methylation levels were elevated for ERCC1 and XRCC1 during carcinogenesis, an inverse correlation with protein expression was found only for BRCA1 and MLH1. These results suggest that a continuous accumulation of DNA repair gene hypermethylation and the consequent protein alterations might be a vital molecular mechanism during the process of multistep chemical-induced rat lung carcinogenesis.

MSI phenotype and MMR alterations in familial and sporadic gastric cancer

Microsatellite instability (MSI) is a major pathway involved in gastric carcinogenesis occurring in 20% of gastric cancer (GC). However, it is not clear whether MSI phenotype preferentially occurs in the sporadic or familial GC, when stringent inclusion criteria are used. The aim of this study was to compare the frequency of MSI and hypermethylation of MLH1 promoter in a large series of familial GC patients (non-HNPCC and non-CDH1-related) and sporadic cases. Additionally, we analysed the immunoexpression of MMR proteins in a fraction of cases. Overall, the frequency of familial GC was 7.1%, and the frequency of hereditary tumours was 4.6%. MSI phenotype and MLH1 hypermethylation frequencies were not statistical different between familial and sporadic GC settings. Further, the MSI phenotype was not associated with any clinico-pathological features studied in the familial GC setting, whereas in the sporadic setting, it was associated with older age, female gender and intestinal histotype. Using our stringent Amsterdam-based clinical criteria to select familial GC (number of cases, age of onset), we verified that sporadic and familial cases differed in gender but shared histopathological features. We verified that the frequency of MSI was similar in familial and sporadic GC settings, demonstrating that this molecular phenotype is not a hallmark of familial GC in contrast to what is verified in HNPCC. Moreover, we observed that the frequency of MLH1 hypermethylation is similar in sporadic and familial cases suggesting that in both settings MSI is not associated to MMR genetic alterations but in contrast to epigenetic deregulation.

Molecular characterization of late stomal recurrence following total laryngectomy

The goal was to determine recurrent or second primary status for late stomal malignancies, 16 and 17 years post-total laryngectomy in two laryngeal squamous cell carcinoma (LSCC) patients, based on DNA methylation signatures and HPV typing. Adopting a literature review based definition of late stomal recurrences as new primaries at the site of the stoma or neopharynx occurring >5 years after total laryngectomy, we employed a multi-gene candidate approach to examine promoter methylation in 24 tumor suppressor genes and PCR-based assays for HPV status offered additional insights into whether the late stomal tumors post-total laryngectomy were related or not. The primary tumor for Patient 1 was negative for HPV but had aberrant hypermethylation of APC, MLH1 and BRCA1. The stomal biopsy 17-years later showed presence of HPV-16 without any methylated genes. In Patient 2, HPV-11 and promoter methylation of APC identified in the primary tumor was also observed in the stomal malignancy 16 years post-total laryngectomy. Additional information provided by molecular typing for HPV and methylation markers underscored Patient 1's and 2's late stomal presentation as most likely a second primary and recurrence, respectively. DNA methylation markers are particularly advantageous because DNA methylation is an early event in tumorigenesis, and the epigenetic modification, 5-methylcytosine, is a stable marker. Molecular marks to discern genetic heterogeneity or relatedness of stomal malignancies several years post-total laryngectomy can provide clues to their status as either second primaries or likely recurrences. Our results support the hypothesis that a subset of stomal recurrences after total laryngectomy represents second primary tumors.

Gemcitabine Functions Epigenetically by Inhibiting Repair Mediated DNA Demethylation

Gemcitabine is a cytotoxic cytidine analog, which is widely used in anti-cancer therapy. One mechanism by which gemcitabine acts is by inhibiting nucleotide excision repair (NER). Recently NER was implicated in Gadd45 mediated DNA demethylation and epigenetic gene activation. Here we analyzed the effect of gemcitabine on DNA demethylation. We find that gemcitabine inhibits specifically Gadd45a mediated reporter gene activation and DNA demethylation, similar to the topoisomerase I inhibitor camptothecin, which also inhibits NER. In contrast, base excision repair inhibitors had no effect on DNA demethylation. In Xenopus oocytes, gemcitabine inhibits DNA repair synthesis accompanying demethylation of oct4. In mammalian cells, gemcitabine induces DNA hypermethylation and silencing of MLH1. The results indicate that gemcitabine induces epigenetic gene silencing by inhibiting repair mediated DNA demethylation. Thus, gemcitabine can function epigenetically and provides a tool to manipulate DNA methylation.

Abstract A92: Preliminary report on the methylation status of CDKN2A and MLH1 genes in Puerto Rican patients with acute myeloid leukemia

Abstract In acute myeloid leukemias, aberrant DNA methylation of promoter-associated CpG islands represents an important mechanism in leukemogenesis. Hypermethylation of promoters blocks transcriptional activity of genes associated with tumor suppression and cell cycle control. In this study, we evaluate the promoter methylation status of genes CDKN2A and MLH1 in a small sample of Puertorrican patients with acute myeloid leukemia. Methods: Peripheral blood was obtained from 6 patients with acute myeloid leukemia at the time of their diagnosis. Mononuclear cells were isolated by density gradient technique. DNA was isolated and further modified with sodium bisulfite. Methylation-specific polymerase (MSP) chain reaction was performed to detect the aberrant promoter methylation of CDKN2A and MLH1 genes in 6 patients with acute myeloid leukemia. Results: A total of 6 samples were analyzed. The mean age was 44 years (24-66) and most of the patients were female (5/6,83%). Four of the patients had diploid cytogenetics, one patient had t(8;21) and one had-7q cytogenetics. WBC counts at presentation were 5.35/uL (0.8-13.8). Hypermethylation of CDKN2A and MLH1 was not detected in any of the samples. Conclusions: Hypermethylation of CDKN2Aand MLH1 was not seen in the first six samples analyzed in this cohort of Puertorrican patients. Collection of more patient's samples and correlation with clinical data is ongoing. Citation Information: Cancer Epidemiol Biomarkers Prev 2010;19(10 Suppl):A92.

Prevalence and characteristics of hereditary nonpolyposis colon cancer (HNPCC) syndrome in immigrant Chinese cancer patients.

e12019 Background: Hereditary nonpolyposis colon cancer (HNPCC) syndrome is a hereditary disorder that predisposes to colon, endometrial, and gastric cancers before 50 years old. Molecular diagnoses, by testing microsatellite instability (MSI), or immunohistochemical staining (IHC) of the lack of the mismatch repair (MMR) protein expression and genomic sequencing of the MMR genes, is more sensitive and specific than the clinical diagnostic criteria, such as Amsterdam or Bethesda criteria. HNPCC affects 2-5% of Caucasian population. We aim in this study to evaluate the prevalence and clinical characteristics of HNPCC in Chinese patients (immigrants) newly diagnosed of colon, endometrial, and gastric cancer. Methods: Patients of Chinese ethnicity diagnosed of colorectal, endometrial, or gastric cancer in Maimonides Medical Center from 2000 to 2009 were eligible and 150 cases were identified. Medical records were reviewed and IHC staining of four MMR genes, namely MLH1, MSH2, MSH6, and PMS2 were performed on primary tumor specimens. Results: Forty-nine cases were studied so far, 33 of colon cancer, 3 of endometrial cancer and 13 of gastric cancer. There were 24 males and 25 females, age ranges from 32 to 93 years old. Nine patients (4 colon cancers and 5 gastric cancers) were diagnosed at age younger than 50 years old, and none had deficiency of MMR expression by IHC. Two abnormal cases were detected as described below and were confirmed in Ohio State University. Conclusions: Colon cancer with suspected HNPCC MSH6 mutation can have first presentation in patients greater than 50 years old in Chinese patients. The prevalence and characteristics of HNPCC in Chinese patients warrants further study, which is still ongoing. Case Age Gender Cancer site Tumor grade and differentiation Family history IHC staining result and interpretation 1 66 M Ascending colon T2N0M0 adeno ca, moderately differentiated None MSH6 negative, suggestive of HNPCC 2 86 F Ascending colon T1N0M0 adeno ca, poorly differentiated, mucin production None MLH1, PMS2 negative, consistent with MLH1 hypermethylation No significant financial relationships to disclose.

Early onset MSI-H colon cancer with MLH1 promoter methylation, is there a genetic predisposition?

BackgroundTo investigate the etiology of MLH1 promoter methylation in mismatch repair (MMR) mutation-negative early onset MSI-H colon cancer. As this type of colon cancer is associated with high ages, young patients bearing this type of malignancy are rare and could provide additional insight into the etiology of sporadic MSI-H colon cancer.MethodsWe studied a set of 46 MSI-H colon tumors cases with MLH1 promoter methylation which was enriched for patients with an age of onset below 50 years (n = 13). Tumors were tested for CIMP marker methylation and mutations linked to methylation: BRAF, KRAS, GADD45A and the MLH1 -93G>A polymorphism. When available, normal colon and leukocyte DNA was tested for GADD45A mutations and germline MLH1 methylation. SNP array analysis was performed on a subset of tumors.ResultsWe identified two cases (33 and 60 years) with MLH1 germline promoter methylation. BRAF mutations were less frequent in colon cancer patients below 50 years relative to patients above 50 years (p-value: 0.044). CIMP-high was infrequent and related to BRAF mutations in patients below 50 years. In comparison with published controls the G>A polymorphism was associated with our cohort. Although similar distribution of the pathogenic A allele was observed in the patients with an age of onset above and below 50 years, the significance for the association was lost for the group under 50 years. GADD45A sequencing yielded an unclassified variant. Tumors from both age groups showed infrequent copy number changes and loss-of-heterozygosity.ConclusionSomatic or germline GADD45A mutations did not explain sporadic MSI-H colon cancer. Although germline MLH1 methylation was found in two individuals, locus-specific somatic MLH1 hypermethylation explained the majority of sporadic early onset MSI-H colon cancer cases. Our data do not suggest an intrinsic tendency for CpG island hypermethylation in these early onset MSI-H tumors other than through somatic mutation of BRAF.

Hereditary and Familial Colon Cancer

Between 2% to 5% of all colon cancers arise in the setting of well-defined inherited syndromes, including Lynch syndrome, familial adenomatous polyposis, MUTYH-associated polyposis, and certain hamartomatous polyposis conditions. Each is associated with a high risk of colon cancer. In addition to the syndromes, up to one-third of colon cancers exhibit increased familial risk, likely related to inheritance. A number of less penetrant, but possibly more frequent susceptibility genes have been identified for this level of inheritance. Clarification of predisposing genes allows for accurate risk assessment and more precise screening approaches. This review examines the colon cancer syndromes, their genetics and management, and also the common familial colon cancers with current genetic advances and screening guidelines.

Recent insights into the pathogenesis of colorectal cancer

Colorectal cancer (CRC) is one of the leading causes of cancer-related deaths in the Western world, but our understanding of this disease is incomplete. The recent advent of new technologies has provided novel insights into the pathogenesis of CRC. Genome-wide association studies have recently linked CRC to 10 common genetic variants or single-nucleotide polymorphisms that map to chromosomes 8q23, 8q24, 10p14, 11q23, 14q22, 15q13, 16q22, 18q21, 19q13 and 20p1. However, the causal significance of these variants is not understood, and some are located in poorly characterized genomic regions or gene deserts. Recent studies indicate that the single-nucleotide polymorphism rs6983267, which maps to 8q24, serves as an enhancer of MYC expression by binding T cell factor 4 (TCF4) and influencing Wnt signaling. In addition, several microRNAs interact with genes such as K-RAS, APC, p53, PTEN, TCF4, COX-2, DNMT3a and DNMT3b. Germline hypermethylation of the DNA mismatch repair genes MLH1 and MSH2 may serve as predisposing events in some CRC patients. Recent studies have elucidated novel mechanisms involved in CRC, including the involvement of single-nucleotide polymorphisms not located within traditional genes, the role of microRNAs and epimutations in DNA mismatch repair genes. Interestingly, most of this progress has been made by understanding DNA that does not encode genes.

Genetic Variants of Methyl Metabolizing Enzymes and Epigenetic Regulators: Associations with Promoter CpG Island Hypermethylation in Colorectal Cancer

Aberrant DNA methylation affects carcinogenesis of colorectal cancer. Folate metabolizing enzymes may influence the bioavailability of methyl groups, whereas DNA and histone methyltransferases are involved in epigenetic regulation of gene expression. We studied associations of genetic variants of folate metabolizing enzymes (MTHFR, MTR, and MTRR), DNA methyltransferase DNMT3b, and histone methyltransferases (EHMT1, EHMT2, and PRDM2), with colorectal cancers, with or without the CpG island methylator phenotype (CIMP), MLH1 hypermethylation, or microsatellite instability. Incidence rate ratios were calculated in case-cohort analyses, with common homozygotes as reference, among 659 cases and 1,736 subcohort members of the Netherlands Cohort Study on diet and cancer (n = 120,852). Men with the MTHFR 677TT genotype were at decreased colorectal cancer risk (incidence rate ratio, 0.49; P = 0.01), but the T allele was associated with increased risk in women (incidence rate ratio, 1.39; P = 0.02). The MTR 2756GG genotype was associated with increased colorectal cancer risk (incidence rate ratio, 1.58; P = 0.04), and inverse associations were observed among women carrying DNMT3b C-->T (rs406193; incidence rate ratio, 0.72; P = 0.04) or EHMT2 G-->A (rs535586; incidence rate ratio, 0.76; P = 0.05) polymorphisms. Although significantly correlated (P < 0.001), only 41.5% and 33.3% of CIMP tumors harbored MLH1 hypermethylation or microsatellite instability, respectively. We observed inverse associations between MTR A2756G and CIMP among men (incidence rate ratio, 0.58; P = 0.04), and between MTRR A66G and MLH1 hypermethylation among women (incidence rate ratio, 0.55; P = 0.02). In conclusion, MTHFR, MTR, DNMT3b, and EHMT2 polymorphisms are associated with colorectal cancer, and rare variants of MTR and MTRR may reduce promoter hypermethylation. The incomplete overlap between CIMP, MLH1 hypermethylation, and microsatellite instability indicates that these related "methylation phenotypes" may not be similar and should be investigated separately.

Germline hypermethylation of MLH1 and EPCAM deletions are a frequent cause of Lynch syndrome

It was shown that Lynch syndrome can be caused by germline hypermethylation of the MLH1 and MSH2 promoters. Furthermore, it has been demonstrated very recently that germline deletions of the 3' region of EPCAM cause transcriptional read-through which results in silencing of MSH2 by hypermethylation. We wanted to determine the prevalence of germline MLH1 promoter hypermethylation and of germline and somatic MSH2 promoter hypermethylation in a large group of Lynch syndrome-suspected patients. From a group of 331 Lynch Syndrome-suspected patients we selected cases, who had no germline MLH1, MSH2, or MSH6 mutation and whose tumors showed loss of MLH1 or MSH2, or, if staining was unavailable, had a tumor with microsatellite instability. Methylation assays were performed to test these patients for germline MLH1 and/or MSH2 promoter hypermethylation. Two patients with germline MLH1 promoter hypermethylation and no patients with germline MSH2 promoter hypermethylation were identified. In the subgroup screened for germline MSH2 promoter hypermethylation, we identified 3 patients with somatic MSH2 promoter hypermethylation in their tumors, which was caused by a germline EPCAM deletion. In the group of 331 Lynch Syndrome-suspected patients, the frequencies of germline MLH1 promoter hypermethylation and somatic MSH2 promoter hypermethylation caused by germline EPCAM deletions are 0.6 and 0.9%, respectively. These mutations, therefore, seem to be rather infrequent. However, the contribution of germline MLH1 hypermethylation and EPCAM deletions to the genetically proven Lynch syndrome cases in this cohort is very high. Previously 27 pathogenic mutations were identified; the newly identified mutations now represent 16% of all mutations.