Microsatellite instability among individuals of Hispanic origin with colorectal cancer

BACKGROUND

Although the presence of microsatellite instability (MSI) in patients with colorectal cancer (CRC) may have implications for prognosis, therapy, and family counseling, to the authors' knowledge, the prevalence of MSI has not been well described among individuals of Hispanic origin with CRC residing in the United States.

METHODS

A retrospective cohort study using a hospital-based tumor registry to identify individuals of Hispanic origin who were diagnosed with CRC was conducted. Clinical data and tumor samples were retrieved. Molecular analyses included testing for MSI using a panel of 5 mononucleotide markers (BAT25, BAT26, NR21, NR24, and NR27) in a pentaplex polymerase chain reaction assay, as well as immunohistochemistry for the mismatch repair (MMR) proteins mutL homolog (MLH) 1, mutS homolog (MSH) 2, MSH6, and postmeiotic segregation increased 2 (PMS2) 2 on representative tissue.

RESULTS

A total of 111 individuals of Hispanic origin with CRC were identified. Approximately 41.4% were women, and the median age was 57 years (interquartile range [IQR], 47.1-63.5 years). Eleven patients (9.9%; 95% confidence interval [95% CI], 4.2%-15.6%) had MSI CRC, whereas 14 patients (12.6%; 95% CI, 7.3%-21.8%) had CRC with ≥1 MMR protein abnormality. Ten of 11 individuals with MSI had clinical or molecular characteristics suspicious for Lynch syndrome such as abnormal expression of MSH2 and/or MSH6 (n=7) or age<50 years at the time of diagnosis (n=7).

CONCLUSIONS

The prevalence of MSI CRC among Hispanic individuals may be similar to that of other races and ethnicities, but clinicopathological characteristics, including age at diagnosis and pattern of abnormal MMR protein expression, suggest that sporadic MSI CRC may be less common in individuals of Hispanic origin, and that much of the MSI observed in this situation may be attributable to Lynch syndrome. Further exploration of the causes of disparate presentations of CRC by ethnicity and race is warranted.

Health benefits and cost-effectiveness of primary genetic screening for Lynch syndrome in the general population

In current clinical practice, genetic testing to detect Lynch syndrome mutations ideally begins with diagnostic testing of an individual affected with cancer before offering predictive testing to at-risk relatives. An alternative strategy that warrants exploration involves screening unaffected individuals via demographic and family histories, and offering genetic testing to those individuals whose risks for carrying a mutation exceed a selected threshold. Whether this approach would improve health outcomes in a manner that is cost-effective relative to current standards of care has yet to be demonstrated. To do so, we developed a simulation framework that integrated models of colorectal and endometrial cancers with a 5-generation family history model to predict health and economic outcomes of 20 primary screening strategies (at a wide range of compliance levels) aimed at detecting individuals with mismatch repair gene mutations and their at-risk relatives. These strategies were characterized by (i) different screening ages for starting risk assessment and (ii) different risk thresholds above which to implement genetic testing. For each strategy, 100,000 simulated individuals, representative of the U.S. population, were followed from the age of 20, and the outcomes were compared with current practice. Findings indicated that risk assessment starting at ages 25, 30, or 35, followed by genetic testing of those with mutation risks exceeding 5%, reduced colorectal and endometrial cancer incidence in mutation carriers by approximately 12.4% and 8.8%, respectively. For a population of 100,000 individuals containing 392 mutation carriers, this strategy increased quality-adjusted life-years (QALY) by approximately 135 with an average cost-effectiveness ratio of $26,000 per QALY. The cost-effectiveness of screening for mismatch repair gene mutations is comparable to that of accepted cancer screening activities in the general population such as colorectal cancer screening, cervical cancer screening, and breast cancer screening. These results suggest that primary screening of individuals for mismatch repair gene mutations, starting with risk assessment between the ages of 25 and 35, followed by genetic testing of those whose risk exceeds 5%, is a strategy that could improve health outcomes in a cost-effective manner relative to current practice.

Chronic inflammation, colorectal cancer and gene polymorphisms

Chronic inflammation is commonly present in gastrointestinal mucosal sites at increased risk for cancer, such as in inflammatory bowel disease (IBD) or chronic gastritis caused by Helicobacter pylori infection. Why some patients have more mucosal inflammation than others, and why certain individuals with chronic inflammation develop cancer, are problems that have not been solved. Unlike the case for the syndromic forms of familial colorectal cancer (CRC), the risks for IBD and other forms of chronic inflammation have not been linked to highly penetrant single gene mutations. Single nucleotide polymorphisms (SNP) are variations in DNA sequence that can be linked to any phenotype (cancer, chronic inflammation, etc.) in genome-wide association studies (GWAS). CRC has been linked to several highly penetrant single gene loci, as well as multiple SNP. The propensity to develop IBD has not been linked to single gene mutations in most instances, but has been linked to SNP in the NOD2 locus (which appear to create hypomorphic alleles for this bacterial response gene), the IL23R locus, the autophagy gene ATG16L1 and a wide range of other loci including the Toll-like receptors, JAK2 and STAT3, and perhaps 70 more. At present, the problem in predicting risk for chronic inflammation is that there are many genetic polymorphisms with relatively modest individual effects. Our challenge is to understand how the SNPs that are linked to variations in the inflammatory response interact with one another (i.e. to understand the 'epistasis' involved), and to integrate this with the variety of individual environmental exposures. This represents an opportunity for informatics science to help personalize our approach to chronic inflammatory diseases of the gut and identify those at greatest risk for cancer.

Highly purified eicosapentaenoic acid as free fatty acids strongly suppresses polyps in Apc(Min/+) mice

PURPOSE

Although cyclooxygenase (COX)-2 inhibitors could represent the most effective chemopreventive tool against colorectal cancer (CRC), their use in clinical practice is hampered by cardiovascular side effects. Consumption of ω-3-polyunsaturated fatty acids (ω-3-PUFAs) is associated with a reduced risk of CRC. Therefore, in this study, we assessed the efficacy of a novel 99% pure preparation of ω-3-PUFA eicosapentaenoic acid as free fatty acids (EPA-FFA) on polyps in Apc(Min/+) mice.

EXPERIMENTAL DESIGN

Apc(Min/+) and corresponding wild-type mice were fed control diet (Ctrl) or diets containing either EPA-FFA 2.5% or 5%, for 12 weeks while monitoring food intake and body weight.

RESULTS

We found that both EPA-FFA diets protected from the cachexia observed among Apc(Min/+) animals fed Ctrl diet (P < 0.0054), without toxic effect, in conjunction with a significant decrease in lipid peroxidation in the treated arms. Moreover, both EPA-FFA diets dramatically suppressed polyp number (by 71.5% and 78.6%, respectively; P < 0.0001) and load (by 82.5% and 93.4%, respectively; P < 0.0001) in both small intestine and colon. In addition, polyps less than 1 mm in size were predominantly found in the EPA-FFA 5% arm whereas those 1 to 3 mm in size were more frequent in the Ctrl arm (P < 0.0001). Interestingly, in the EPA-FFA groups, mucosal arachidonic acid was replaced by EPA (P < 0.0001), leading to a significant reduction in COX-2 expression and β-catenin nuclear translocation. Moreover, in the EPA-FFA arms, we found a significant decrease in proliferation throughout the intestine together with an increase in apoptosis.

CONCLUSIONS

Our data make 99% pure EPA-FFA an excellent candidate for CRC chemoprevention.

Making sense of missense in Lynch syndrome: the clinical perspective

The DNA mismatch repair (MMR) system provides critical genetic housekeeping, and its failure is associated with tumorigenesis. Through distinct domains on the DNA MMR proteins, the system recognizes and repairs errors occurring during DNA synthesis, but signals apoptosis when the DNA damage cannot be repaired. Certain missense mutations in the MMR genes can selectively alter just one of these functions. This affects the clinical features of tumors associated with defective DNA MMR activity. New work reported by Xie et al. in this issue of the journal (beginning on page 1409) adds to the understanding of DNA MMR.

MSH6 and MUTYH deficiency is a frequent event in early-onset colorectal cancer

PURPOSE

Early-onset colorectal cancer (CRC) is suggestive of a hereditary predisposition. Lynch syndrome is the most frequent CRC hereditary cause. The MUTYH gene has also been related to hereditary CRC. A systematic characterization of these two diseases has not been reported previously in this population.

EXPERIMENTAL DESIGN

We studied a retrospectively collected series of 140 patients ≤50 years old diagnosed with nonpolyposis CRC. Demographic, clinical, and familial features were obtained. Mismatch repair (MMR) deficiency was determined by microsatellite instability (MSI) analysis, and immunostaining for MLH1, MSH2, MSH6, and PMS2 proteins. Germline MMR mutations were evaluated in all MMR-deficient cases. Tumor samples with loss of MLH1 or MSH2 protein expression were analyzed for somatic methylation. Germline MUTYH mutations were evaluated in all cases. BRAF V600E and KRAS somatic mutational status was also determined.

RESULTS

Fifteen tumors (11.4%) were MSI, and 20 (14.3%) showed loss of protein expression (7 for MLH1/PMS2, 2 for isolated MLH1, 3 for MSH2/MSH6, 7 for isolated MSH6, and 1 for MSH6/PMS2). We identified 11 (7.8%) germline MMR mutations, 4 in MLH1, 1 in MSH2, and 6 in MSH6. Methylation analysis revealed one case with somatic MLH1 methylation. Biallelic MUTYH mutations were detected in four (2.8%) cases. KRAS and BRAF V600E mutations were present in 39 (27.9%) and 5 (3.6%) cases, respectively.

CONCLUSIONS

Loss of MSH6 expression is the predominant cause of MMR deficiency in early-onset CRC. Our findings prompt the inclusion of MSH6 and MUTYH screening as part of the genetic counseling of these patients and their relatives.

Epigenetic silencing of miR-137 is an early event in colorectal carcinogenesis

Global downregulation of microRNAs (miRNA) is a common feature in colorectal cancer (CRC). Whereas CpG island hypermethylation constitutes a mechanism for miRNA silencing, this field largely remains unexplored. Herein, we describe the epigenetic regulation of miR-137 and its contribution to colorectal carcinogenesis. We determined the methylation status of miR-137 CpG island in a panel of six CRC cell lines and 409 colorectal tissues [21 normal colonic mucosa from healthy individuals (N-N), 160 primary CRC tissues and their corresponding normal mucosa (N-C), and 68 adenomas]. TaqMan reverse transcription-PCR and in situ hybridization were used to analyze miR-137 expression. In vitro functional analysis of miR-137 was performed. Gene targets of miR-137 were identified using a combination of bioinformatic and transcriptomic approaches. We experimentally validated the miRNA:mRNA interactions. Methylation of the miR-137 CpG island was a cancer-specific event and was frequently observed in CRC cell lines (100%), adenomas (82.3%), and CRC (81.4%), but not in N-C (14.4%; P < 0.0001 for CRC) and N-N (4.7%; P < 0.0001 for CRC). Expression of miR-137 was restricted to the colonocytes in normal mucosa and inversely correlated with the level of methylation. Transfection of miR-137 precursor in CRC cells significantly inhibited cell proliferation. Gene expression profiling after miR-137 transfection discovered novel potential mRNA targets. We validated the interaction between miR-137 and LSD-1. Our data indicate that miR-137 acts as a tumor suppressor in the colon and is frequently silenced by promoter hypermethylation. Methylation silencing of miR-137 in colorectal adenomas suggests it to be an early event, which has prognostic and therapeutic implications.

Mutations in TGFbeta-RII and BAX mediate tumor progression in the later stages of colorectal cancer with microsatellite instability

BACKGROUND

Microsatellite instability (MSI) occurs in 15% of colorectal cancers (CRC). The genetic targets for mutation in the MSI phenotype include somatic mutations in the transforming growth factor beta receptor typeII (TGFbetaRII), BAX, hMSH3 and hMSH6. It is not clear how mutations of these genes mediate tumor progression in the MSI pathway, and the temporal sequence of these mutations remains uncertain. In this study, early stage CRCs were examined for frameshift mutations in these target genes, and compared with late stage tumors and CRC cell lines.

METHODS

We investigated 6 CRC cell lines and 71 sporadic CRCs, including 61 early stage cancers and 10 late stage cancers. Mutations of repetitive mononucleotide tracts in the coding regions of TGFbetaRII, BAX, hMSH3, hMSH6, IGFIIR and Fas antigen were identified by direct sequencing.

RESULTS

Thirteen (18.3%) of 71 CRC, including 9/61 (14.7%) early stage cancers and 4/10 (40%) late stage cancers, were identified as MSI and analyzed for frameshift mutations. No mutation in the target genes was observed in any of the 9 early stage MSI CRCs. In contrast, frameshift mutations of TGFbetaRII, BAX, hMSH3 and hMSH6 were present in 3/4 late stage MSI tumors. There is a statistical association (p = 0.014) between mutation in any one gene and tumor stage.

CONCLUSIONS

TGFbetaRII, BAX, hMSH3 and hMSH6 mutations are relatively late events in the genesis of MSI CRCs. The frameshift mutations in these target genes might mediate progression from early to late stage cancer, rather than mediating the adenoma to carcinoma transition.

Fecal MicroRNAs as novel biomarkers for colon cancer screening

INTRODUCTION

Colorectal cancer (CRC) is the second leading cause of cancer-related deaths, but currently available noninvasive screening programs have achieved only a modest decrease in mortality. MicroRNAs (miRNA) play an important role in a wide array of biological processes and are commonly dysregulated in neoplasia. We aimed to evaluate the feasibility of fecal miRNAs as biomarkers for colorectal neoplasia screening.

MATERIALS AND METHODS

Total RNA was extracted from freshly collected stool samples from 8 healthy volunteers and 29 samples collected via fecal occult blood testing from subjects with normal colonoscopies, colon adenomas, and CRCs. miRNA expression analyses were done with TaqMan quantitative reverse transcription-PCR for a subset of miRNAs. Illumina miRNA microarray profiling was done to evaluate the differences in expression patterns between normal colonic mucosa tissues and stool samples from healthy subjects.

RESULTS

We efficiently extracted miRNAs from stool specimens using our developed protocol. Data from independent experiments showed high reproducibility for miRNA extraction and expression. miRNA expression patterns were similar in stool specimens among healthy volunteers, and reproducible in stool samples that were collected serially in time from the same individuals. miRNA expression profiles from 29 patients showed higher expression of miR-21 and miR-106a in patients with adenomas and CRCs compared with individuals free of colorectal neoplasia.

CONCLUSION

Our data indicate that miRNAs could be extracted from stool easily and reproducibly. The stools of patients with colorectal neoplasms have unique and identifiable patterns of miRNA expression.

IMPACT

Fecal miRNAs may be an excellent candidate for the development of a noninvasive screening test for colorectal neoplasms.

Report from the Jerusalem workshop on Lynch syndrome-hereditary nonpolyposis colorectal cancer

A Workshop was held in Jerusalem, Israel, on October 26 and 27, 2009 to discuss the management of Lynch syndrome-hereditary nonpolyposis colorectal cancer (CRC), with the primary goal to develop consensus for the optimal management of this disease. A second goal was to identify areas of research with the potential to advance the clinical management of Lynch syndrome. The perspectives and recommendations from the workshop are meant to be a platform for discussion and deliberation. The Workshop was organized by Moshe Shike (Memorial Sloan Kettering Cancer Center, New York) and sponsored by The Colon Cancer Foundation. More details of each presentation are available in an on-line supplement.

Microsatellite instability in colorectal cancer

Microsatellite instability (MSI) is a hypermutable phenotype caused by the loss of DNA mismatch repair activity. MSI is detected in about 15% of all colorectal cancers; 3% are of these are associated with Lynch syndrome and the other 12% are caused by sporadic, acquired hypermethylation of the promoter of the MLH1 gene, which occurs in tumors with the CpG island methylator phenotype. Colorectal tumors with MSI have distinctive features, including a tendency to arise in the proximal colon, lymphocytic infiltrate, and a poorly differentiated, mucinous or signet ring appearance. They have a slightly better prognosis than colorectal tumors without MSI and do not have the same response to chemotherapeutics. Discovery of MSI in colorectal tumors has increased awareness of the diversity of colorectal cancers and implications for specialized management of patients.

Aberrant DNA methylation in hereditary nonpolyposis colorectal cancer without mismatch repair deficiency

BACKGROUND & AIMS

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.

METHODS

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.

RESULTS

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.

CONCLUSIONS

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.

The nucleotide composition of microsatellites impacts both replication fidelity and mismatch repair in human colorectal cells

Microsatellite instability is a key mechanism of colon carcinogenesis. We have previously studied mutations within a (CA)13 microsatellite using an enhanced green fluorescent protein (EGFP)-based reporter assay that allows the distinction of replication errors and mismatch repair (MMR) activity. Here we utilize this assay to compare mutations of mono- and dinucleotide repeats in human colorectal cells. HCT116 and HCT116+chr3 cells were stably transfected with EGFP-based plasmids harboring A10, G10, G16, (CA)13 and (CA)26 repeats. EGFP-positive mutant fractions were quantitated by flow cytometry, mutation rates were calculated and the mutant spectrum was analyzed by cycle sequencing. EGFP fluorescence pattern changed with the microsatellite's nucleotide sequence and cell type and clonal variations were observed in mononucleotide repeats. Replication errors (as calculated in HCT116) at A10 repeats were 5–10-fold higher than in G10, G16 were 30-fold higher than G10 and (CA)26 were 10-fold higher than (CA)13. The mutation rates in hMLH1-proficient HCT116+chr3 were 30–230-fold lower than in HCT116. MMR was more efficient in G16 than in A10 clones leading to a higher stability of poly-G tracts. Mutation spectra revealed predominantly 1-unit deletions in A10, (CA)13 and G10 and 2-unit deletions or 1-unit insertion in (CA)26. These findings indicate that both replication fidelity and MMR are affected by the microsatellite's nucleotide composition.

Somatic hypermethylation of MSH2 is a frequent event in Lynch Syndrome colorectal cancers

Heritable germline epimutations in MSH2 have been reported in a few Lynch syndrome families that lacked germline mutations in the MSH2 gene. It is not known whether somatic MSH2 methylation occurs in MSH2 mutation-positive Lynch syndrome subjects or sporadic colorectal cancers (CRC). Therefore, we determined the methylation status of the MSH2 gene in 268 CRC tissues, including 222 sporadic CRCs and 46 Lynch syndrome tumors that did not express MSH2. We also looked for microsatellite instability (MSI), germline mutations in the MSH2 and EpCAM genes, somatic mutations in BRAF and KRAS, and the CpG island methylator phenotype (CIMP). We observed that somatic MSH2 hypermethylation was present in 24% (11 of 46) of MSH2-deficient (presumed Lynch syndrome) tumors, whereas no evidence for MSH2 methylation existed in sporadic CRCs (MSI and microsatellite stable) or normal colonic tissues. Seven of 11 (63%) patients with MSH2 methylation harbored simultaneous pathogenic germline mutations in the MSH2 gene. Germline EpCAM deletions were present in three of four patients with MSH2 methylation but without pathogenic MSH2 germline mutations. The mean methylation scores at CIMP-related markers were significantly higher in Lynch syndrome tumors with MSH2 methylation than MSH2-unmethylated CRCs. In conclusion, our data provide evidence for frequent MSH2 hypermethylation in Lynch syndrome tumors with MSH2 deficiency. MSH2 methylation in this subset of individuals is somatic and may serve as the "second hit" at the wild-type allele. High levels of aberrant methylation at CIMP-related markers in MSH2-methylated tumors raise the possibility that MSH2 is a target susceptible to aberrant methylation in Lynch syndrome.

An optimized pentaplex PCR for detecting DNA mismatch repair-deficient colorectal cancers

Purpose

Microsatellite instability (MSI) is used to screen colorectal cancers (CRC) for Lynch Syndrome, and to predict outcome and response to treatment. The current technique for measuring MSI requires DNA from normal and neoplastic tissues, and fails to identify tumors with specific DNA mismatch repair (MMR) defects. We tested a panel of five quasi-monomorphic mononucleotide repeat markers amplified in a single multiplex PCR reaction (pentaplex PCR) to detect MSI.

Experimental Design

We investigated a cohort of 213 CRC patients, comprised of 114 MMR-deficient and 99 MMR-proficient tumors. Immunohistochemical (IHC) analysis evaluated the expression of MLH1, MSH2, PMS2 and MSH6. MSI status was defined by differences in the quasi-monomorphic variation range (QMVR) from a pool of normal DNA samples, and measuring differences in allele lengths in tumor DNA.

Results

Amplification of 426 normal alleles allowed optimization of the QMVR at each marker, and eliminated the requirement for matched reference DNA to define MSI in each sample. Using ≥2/5 unstable markers as the criteria for MSI resulted in a sensitivity of 95.6% (95% CI = 90.1–98.1%) and a positive predictive value of 100% (95% CI = 96.6%–100%). Detection of MSH6-deficiency was limited using all techniques. Data analysis with a three-marker panel (BAT26, NR21 and NR27) was comparable in sensitivity (97.4%) and positive predictive value (96.5%) to the five marker panel. Both approaches were superior to the standard approach to measuring MSI.

Conclusions

An optimized pentaplex (or triplex) PCR offers a facile, robust, very inexpensive, highly sensitive, and specific assay for the identification of MSI in CRC.

Microsatellite instability at tetranucleotide repeats in sporadic colorectal cancer in Japan

Most tumors of patients with Lynch syndrome and a fraction of sporadic colorectal cancers (CRCs) exhibit high levels of microsatellite instability (MSI) at mono- and dinucleotide repeat loci. A different type of instability, elevated microsatellite alterations at selected tetranucleotide repeats (EMAST) has been found in non-colonic cancers. Our previous study demonstrated that EMAST is common in sporadic CRC. Here, we focused on the relationships between EMAST and other genomic instability parameters or clinicopathological features in an unselected series of 88 sporadic CRCs. Of the tumors in the sample, 4 (4.5%) were MSI-high (MSI-H), 9 (10.2%) were MSI-low (MSI-L) and 75 (85.2%) were microsatellite stable. EMAST status was determined using 7 EMAST markers. Fifty-three (60.2%) tumors without MSI-H showed instability at >or=1 EMAST loci. All 4 MSI-H tumors showed instability at several EMAST loci. Instability profiles of MSI-H tumors at EMAST loci were more complex than those of non-MSI-H tumors. A tendency of positive association was observed between MSI-L and EMAST (P=0.023). The frequency of loss of heterozygosity (LOH) for the 14 loci in EMAST-positive tumors was significantly higher than negative tumors (P=0.048). Among the clinicopathological parameters, only tumor location at the distal colon was associated with EMAST-negative tumors (P=0.0084, one-tailed). A relatively higher frequency of well-differentiated adenocarcinomas was observed in EMAST tumors as opposed to non-EMAST tumors, though the survival rate was similar. These results suggest that overlapping mechanisms that cause MSI-L, EMAST and LOH in CRCs may exist.

Analysis of fecal DNA methylation to detect gastrointestinal neoplasia

BACKGROUND

The development of noninvasive screening tests is important to reduce mortality from gastrointestinal neoplasia. We sought to develop such a test by analysis of DNA methylation from exfoliated cancer cells in feces.

METHODS

We first analyzed methylation of the RASSF2 and SFRP2 gene promoters from 788 primary gastric and colorectal tissue specimens to determine whether methylation patterns could act as stage-dependent biomarkers of gastrointestinal tumorigenesis. Next, we developed a novel strategy that uses single-step modification of DNA with sodium bisulfite and fluorescence polymerase chain reaction methodology to measure aberrant methylation in fecal DNA. Methylation of the RASSF2 and SFRP2 promoters was analyzed in 296 fecal samples obtained from a variety of patients, including 21 with gastric tumors, 152 with colorectal tumors, and 10 with non-neoplastic or inflammatory lesions in the gastrointestinal lumen.

RESULTS

Analysis of DNA from tissues showed presence of extensive methylation in both gene promoters exclusively in advanced gastric and colorectal tumors. The assay successfully identified one or more methylated markers in fecal DNA from 57.1% of patients with gastric cancer, 75.0% of patients with colorectal cancer, and 44.4% of patients with advanced colorectal adenomas, but only 10.6% of subjects without neoplastic or active diseases (difference, gastric cancer vs undiseased = 46.5%, 95% confidence interval (CI) = 24.6% to 68.4%, P < .001; difference, colorectal cancer vs undiseased = 64.4%, 95% CI = 53.5% to 75.2%, P < .001; difference, colorectal adenoma vs undiseased = 33.8%, 95% CI = 14.2% to 53.4%, P < .001).

CONCLUSIONS

Methylation of the RASSF2 and SFRP2 promoters in fecal DNA is associated with the presence of gastrointestinal tumors relative to non-neoplastic conditions. Our novel fecal DNA methylation assay provides a possible means to noninvasively screen not only for colorectal tumors but also for gastric tumors.

Regulation of colorectal cancer cell apoptosis by the n-3 polyunsaturated fatty acids Docosahexaenoic and Eicosapentaenoic

Several studies have suggested that the n-3 fatty acids Docosahexaenoic (DHA) and Eicosapentaenoic (EPA) have an important protective effect on colorectal cancer, and this could be at least partly due to their proapoptotic activity. It is unclear, however, how this phenomenon is triggered and what mechanisms are implicated. Here, we show that both DHA and EPA have an important proapoptotic effect on colorectal cancer cells with different molecular phenotypes but not in noncancerous cells. Apoptosis is caspase dependent, and both intrinsic and extrinsic pathways are implicated. The dimerization of Bax and Bak, the depolarization of the mitochondrial membrane, and the subsequent release of cytochrome c and Smac/Diablo to the cytosol evidence the activation of the intrinsic pathway. The implication of the extrinsic pathway is shown by the activation of caspase-8, along with the down-regulation of FLIP. The timing of caspase-8 activation, and the oligomerization of Bid with Bax, suggest a cross-talk with the intrinsic pathway. None of the death receptors that commonly initiate the extrinsic pathway: FAS, TNF-R1, and TRAIL-R2 are found to be responsible for triggering the apoptosis cascade induced by DHA and EPA. Neither PPARgamma nor cyclooxygenase-2, two likely candidates to regulate this process, play a significant role. Our findings suggest that the down-regulation of two key regulatory elements of the extrinsic and intrinsic pathways, FLIP and XIAP, respectively, is determinant in the induction of apoptosis by DHA and EPA. These fatty acids could potentially be useful adjuvant anticancer agents in combination with other chemotherapeutic elements.

Allelic imbalance at p53 and microsatellite instability are predictive markers for resistance to chemotherapy in gastric carcinoma

BACKGROUND

Combined treatment with 5-fluorouracil and cisplatin (FP chemotherapy) is an effective neoadjuvant regimen for gastric carcinoma. However, it is ineffective in half of all patients. This study tests the hypothesis that genetic markers might identify those patients with gastric cancer who would respond to neoadjuvant FP chemotherapy.

MATERIALS AND METHODS

A total of 23 patients with gastric carcinoma were treated with neoadjuvant chemotherapy. Pretreatment biopsy specimens before neoadjuvant chemotherapy were obtained from 15 of 23 patients, and resected tumors were obtained from all 23. Genetic studies were performed to detect allelic imbalance (AI), microsatellite instability (MSI), and K-ras mutation.

RESULTS

A clinical response was observed in 13 of 23 patients. Kaplan-Meier survival curve showed that clinical responder group had a significantly higher likelihood of overall survival (P = 0.0165), compared with nonresponder group. In 23 resection specimens, 10 of 23 tumors presented AI at the p53 locus and/or MSI; 8 of the 10 tumors were nonresponders, while 12 of 13 tumors without p53 AI or MSI were responders (P = 0.0007). In 15 pretreatment biopsy specimens, 8 tumors had p53 AI and/or MSI; 7 of the 8 tumors were nonresponders, while 6 of 7 tumors without p53 AI or MSI were responders to preoperative chemotherapy (P = 0.008). Tumors with AI at the p53 locus and/or MSI were significantly more resistant to neoadjuvant chemotherapy. No relationship was found between K-ras mutations and responses.

CONCLUSIONS

Analysis for p53 AI and MSI might represent a clinically useful approach to predicting the response to neoadjuvant FP chemotherapy in gastric carcinoma.

Review of the Lynch syndrome: history, molecular genetics, screening, differential diagnosis, and medicolegal ramifications

More than one million patients will manifest colorectal cancer (CRC) this year of which, conservatively, approximately 3% (approximately 30,700 cases) will have Lynch syndrome (LS), the most common hereditary CRC predisposing syndrome. Each case belongs to a family with clinical needs that require genetic counseling, DNA testing for mismatch repair genes (most frequently MLH1 or MSH2) and screening for CRC. Colonoscopy is mandated, given CRC's proximal occurrence (70-80% proximal to the splenic flexure). Due to its early age of onset (average 45 years of age), colonoscopy needs to start by age 25, and because of its accelerated carcinogenesis, it should be repeated every 1 to 2 years through age 40 and then annually thereafter. Should CRC occur, subtotal colectomy may be necessary, given the marked frequency of synchronous and metachronous CRC. Because 40-60% of female patients will manifest endometrial cancer, tailored management is essential. Additional extracolonic cancers include ovary, stomach, small bowel, pancreas, hepatobiliary tract, upper uroepithelial tract, brain (Turcot variant) and sebaceous adenomas/carcinomas (Muir-Torre variant). LS explains only 10-25% of familial CRC.

Phenotypic and genotypic heterogeneity in the Lynch syndrome: diagnostic, surveillance and management implications

Lynch syndrome is the most common form of hereditary colorectal cancer (CRC). This review covers the cardinal features of Lynch syndrome with particular emphasis upon its diagnostic criteria, molecular genetics, natural history, genetic counseling, surveillance and management. Considerable attention has been given to the etiologic role of mismatch repair (MMR) genes as well as low penetrance alleles and modifier genes. The American founder mutation, a deletion of exons 1-6 of MSH2, is discussed in some detail, owing to its high frequency in the US (19 000-30 000 carriers). Genetic counseling is essential prior to patients' undergoing DNA testing and again when receiving their test results. Families with a lower incidence of CRC and extracolonic cancers, in the face of being positive for Amsterdam I criteria but who do not have MMR deficiency by tumor testing, are probably not Lynch syndrome, and thereby should preferably be designated as familial CRC of undetermined type. Patients who are either noncompliant or poorly compliant with colonoscopy, and who are MMR mutation positive, may be candidates for prophylactic colectomy, while MMR mutation-positive women who are noncompliant with gynecologic surveillance may be candidates for prophylactic hysterectomy and bilateral salpingo-oophorectomy.

Microsatellite instability, MLH1 promoter methylation, and BRAF mutation analysis in sporadic colorectal cancers of different ethnic groups in Israel

BACKGROUND

The molecular mechanisms that underlie colorectal cancer (CRC) include microsatellite instability (MSI), chromosomal instability, and the CpG island methylator phenotype. There is evidence to suggest that CRC incidence varies among different ethnic populations worldwide. The authors of this report hypothesized that environmental factors and lifestyle differences among various ethnic groups may differentially influence the epigenetic regulation of tumor suppressor genes in CRC.

METHODS

In the current study, microdissection and DNA extraction were performed on 128 samples of CRC from Israeli patients (85 Jews and 43 Arabs). MSI analysis, mutL homolog 1 (MLH1) and mutS homolog 2 (MSH2) protein expression levels, and MLH1 promoter methylation were investigated by combined bisulfite restriction analysis. The v-raf murine sarcoma viral oncogene homolog B1 (BRAF) valine-to-glutamic acid mutation at residue 600 was investigated by direct DNA sequencing.

RESULTS

High MSI (MSI-H), MLH1 methylation, and BRAF mutations were observed in 11.6%, 9.4%, and 23.5% of Jews, respectively, and in 16.2%, 17.6%, and 20.9% of Arabs, respectively (P value nonsignificant). MLH1 promoter methylation was observed in 22.6% of microsatellite-stable (MSS) tumors and in 53.8% of MSI-H tumors (P < .015). Extensive methylation (covering both 5' and 3' promoter regions) was present in all MSI-H tumors with loss of MLH1 expression. BRAF mutation was observed in 15.6% and 46.1% of MSS tumors and MSI-H tumors, respectively (P < .007). BRAF mutation was observed in 66%, 22.2%, and 14.7% of patients who had tumors with extensive MLH1 promoter methylation, methylation of the 5' region alone, or without methylation, respectively (P < .006).

CONCLUSIONS

There was no difference in molecular signatures examined between Jewish and Arab patients with CRC in Israel. Extensive promoter methylation was associated with MLH1 inactivation, MSI, and BRAF mutation.