Microsatellite instability in esophageal adenocarcinoma

Unveiling STRs instability in a colorectal cancer FFPE sample: a case report

In forensic genetics, sometimes formalin-fixed paraffin-embedded (FFPE) biopsy material taken during life is the only biological sample available for individual identification or paternity testing. In most cases, this biological tissue is characterized by the presence of tumor cells characterized by instability and loss of heterozygosity of microsatellites (MSI/LOH) compared to the DNA present in cells of normal tissue.In this case report, two FFPE samples from the same male subject were available for genetic investigation: one sample with colorectal cancer tissue and the other with normal tissue (no cancerous histopathological features). The comparison of the genetic profiles obtained from DNA extracted from the two tissues showed in the tumor tissue the presence of three genomic instability phenomena affecting FGA, CSF1P0, D21S2055 loci, located on three distinct autosomal chromosomes, and one duplication phenomenon affecting the DYS438. Therefore, due to the MSI/LOH phenomena, the genetic profile acquired from the tumor tissue was distorted and thus generated a fictitious genetic profile, not corresponding to the subject's real one (normal tissue free of tumor cells).

Targeted genetic and epigenetic profiling of esophageal adenocarcinomas and non-dysplastic Barrett's esophagus

Background

Despite the efforts to describe the molecular landscape of esophageal adenocarcinoma (EAC) and its precursor lesion Barrett’s esophagus (BE), discrepant findings are reported. Here, we investigated the prevalence of selected genetic (TP53 mutations and microsatellite instability (MSI) status) and epigenetic (DNA promoter hypermethylation of APC, CDKN2A, MGMT, TIMP3 and MLH1) modifications in a series of 19 non-dysplastic BE and 145 EAC samples. Additional biopsies from adjacent normal tissue were also evaluated. State-of-the-art methodologies and well-defined scoring criteria were applied in all molecular analyses.

Results

Overall, we confirmed frequent TP53 mutations among EAC (28%) in contrast to BE, which harbored no mutations. We demonstrated that MSI and MLH1 promoter hypermethylation are rare events, both in EAC and in BE. Our findings further support that APC, CDKN2A, MGMT and TIMP3 promoter hypermethylation is frequently seen in both lesions (21–89%), as well as in a subset of adjacent normal samples (up to 12%).

Conclusions

Our study further enlightens the molecular background of BE and EAC. To the best of our knowledge, this is one of the largest studies addressing a targeted analysis of genetic and epigenetic modifications simultaneously across a combined series of non-dysplastic BE and EAC samples.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13148-022-01287-7.

Occurrence of High Microsatellite-Instability/Mismatch Repair Deficiency in Nearly 2,000 Human Adenocarcinomas of the Gastrointestinal Tract, Pancreas, and Bile Ducts: A Study From a Large German Comprehensive Cancer Center

INTRODUCTION

Knowledge of the high microsatellite-instability (MSI-H)/mismatch repair deficiency (MMRd) status is of increasing interest for personalized neoadjuvant or adjuvant therapy planning. Only a few studies are available on MSI-H distribution in the Northern European Caucasian patient population. In this study, we focused on a large cohort of tumors of the upper gastrointestinal tract.

MATERIALS AND METHODS

Surgical material from a total of 1,965 patients was analyzed for MSI-H/MMRd status (including 1,267 carcinomas of the esophagus or stomach). All tumors were analyzed with an internationally recommended immunohistochemical panel consisting of four antibodies (MLH1, MSH2, PMS2, and MSH6). The results were molecularly objectified.

RESULTS

Adenocarcinomas with MSI-H/MMRd were detected with the following distribution: esophagus (1.4%), stomach (8.3%), small intestine (18.2%), large intestine (8.5%), intrahepatic bile ducts (1.9%), and pancreas (0%). In case of gastric tumors with MSI-H/MMRd, neoadjuvant therapy did not influence the prognosis of patients (p = 0.94). Within all tumor entities with MSI-H/MMRd, patients with a UICC stage 4 were also represented. In this advanced stage, 11.7% of patients with MSS tumors were diagnosed compared to 0.5% of patients with MSI-H tumors relative to the entire tumor collective.

DISCUSSION

In this study, the proportion of MSI-H/MMRd tumors in the stomach is smaller than would have been expected in knowledge of the data published by TCGA or AGRC. Negative prognostic effects regarding MSI-H status and neoadjuvant therapy as described by the MAGIC study group were not seen in our cohort. The extent to which the MSI-H/MMRd status should be known for neoadjuvant therapy planning must be clarified in prospective studies in the future. At present, there is no convincing data to dispense the neoadjuvant therapy for gastric carcinoma. Due to the very convincing, positive data regarding the response rates of MSI-H tumors to treatment with PD1/PD-L1 inhibitors, every metastatic carcinoma of the gastrointestinal tract should be tested for its MSI-H status.

Microsatellite instability in metaplasia-dysplasia-adenocarcinoma sequence of Barrett esophagus: a retrospective study

Aim

To analyze the loss of mismatch repair (MMR) system protein expression in metaplasia-dysplasia-adenocarcinoma sequence of Barrett esophagus (BE).

Methods

This study retrospectively analyzed the data from 70 patients with pathohistological diagnosis of BE or esophageal adenocarcinoma (EAC) treated at the Clinical Department of Pathology and Cytology, University Hospital Center Zagreb, from January 2009 to January 2011. Patients were divided into three groups: BE without dysplasia (22 patients), BE with dysplasia (37 patients), and EAC (11 patients). Immunohistochemical expression of MutL homologue 1 (MLH1), MutS homologue 2 (MSH2), postmeiotic segregation increased 2 (PMS2), and MutS homologue 6 (MSH6) of DNA MMR system was measured and compared with tumor protein p53 expression.

Results

A total of 81.8% and 81.8% patients with EAC, 32.4% and 35.1% patients with dysplasia, and 50% and 54.5% patients without dysplasia had loss of MLH1 and PMS2 expression, respectively. Patients with EAC and patients with dysplasia did not have loss of MSH2 and MSH6 expression, and 18.2% patients without dysplasia had loss of MSH2 and MSH6 expression. There was a strong positive correlation between MLH1 and PMS2 expression (Spearman ρ 0.97; P < 0.001) and between MSH2 and MSH6 expression (Spearman ρ 0.90, P < 0.001) in the entire sample and in all BE groups. No significant correlations of MLH1 and PMS2 with p53 expression were found, except in dysplasia group (φ 0.402, P = 0.030 for MSH1; φ 0.371, P = 0.042 for PMS2).

Conclusion

Although we demonstrated considerable loss of MLH1 and PMS2 expression in BE-associated carcinoma sequence, due to the retrospective study design and low number of patients we cannot conclude that MLH1 and PMS2 can be used as biomarkers for patient surveillance and therapy-making decisions.

Oxford Centre for Evidence-based Medicine level of evidence: 3

Epstein-Barr virus and mismatch repair deficiency status differ between oesophageal and gastric cancer: A large multi-centre study

BACKGROUND

Oesophageal (OeC) and gastric (GC) cancer patients are treated with similar multimodal therapy and have poor survival. There remains an urgent clinical need to identify biomarkers to individualise patient management and improve outcomes. Therapy with immune checkpoint inhibitors has shown promising results in other cancers. Proposed biomarkers to predict potential response to immune checkpoint inhibitors include DNA mismatch repair (MMR) and/or Epstein-Barr virus (EBV) status. The aim of this study was to establish and compare EBV status and MMR status in large multi-centre series of OeC and GC.

METHODS

EBV was assessed by EBV-encoded RNA (EBER) in situ hybridisation and MMR protein expression by immunohistochemistry (IHC) in 988 OeC and 1213 GC from multiple centres. In a subset of OeC, microsatellite instability (MSI) was tested in parallel with MMR IHC.

RESULTS

Frequency of MMR deficiency (MMRdef) and MSI was low in OeC (0.8% and 0.6%, respectively) compared with GC (10.3%). None of the OeCs were EBER positive in contrast to 4.8% EBER positive GC. EBV positive GC patients were younger (p = 0.01), more often male (p = 0.001) and had a better overall survival (p = 0.012). MMRdef GC patients were older (p = 0.001) and showed more often intestinal-type histology (p = 0.022).

CONCLUSIONS

This is the largest study to date indicating that EBV and MMRdef do not play a role in OeC carcinogenesis in contrast to GC. The potential clinical usefulness of determining MMRdef/EBV status to screen patients for eligibility for immune-targeting therapy differs between OeC and GC patients.

Inflammation-associated microsatellite alterations: Mechanisms and significance in the prognosis of patients with colorectal cancer

Microsatellite alterations within genomic DNA frameshift as a result of defective DNA mismatch repair (MMR). About 15% of sporadic colorectal cancers (CRCs) manifest hypermethylation of the DNA MMR gene MLH1, resulting in mono- and di-nucleotide frameshifts to classify it as microsatellite instability-high (MSI-H) and hypermutated, and due to frameshifts at coding microsatellites generating neo-antigens, produce a robust protective immune response that can be enhanced with immune checkpoint blockade. More commonly, approximately 50% of sporadic non-MSI-H CRCs demonstrate frameshifts at di- and tetra-nucleotide microsatellites to classify it as MSI-low/elevated microsatellite alterations at selected tetranucleotide repeats (EMAST) as a result of functional somatic inactivation of the DNA MMR protein MSH3 via a nuclear-to-cytosolic displacement. The trigger for MSH3 displacement appears to be inflammation and/or oxidative stress, and unlike MSI-H CRC patients, patients with MSI-L/EMAST CRCs show poor prognosis. These inflammatory-associated microsatellite alterations are a consequence of the local tumor microenvironment, and in theory, if the microenvironment is manipulated to lower inflammation, the microsatellite alterations and MSH3 dysfunction should be corrected. Here we describe the mechanisms and significance of inflammatory-associated microsatellite alterations, and propose three areas to deeply explore the consequences and prevention of inflammation's effect upon the DNA MMR system.

Mismatch Repair Deficiency, Microsatellite Instability, and Survival: An Exploratory Analysis of the Medical Research Council Adjuvant Gastric Infusional Chemotherapy (MAGIC) Trial

IMPORTANCE

Mismatch repair (MMR) deficiency (MMRD) and microsatellite instability (MSI) are prognostic for survival in many cancers and for resistance to fluoropyrimidines in early colon cancer. However, the effect of MMRD and MSI in curatively resected gastric cancer treated with perioperative chemotherapy is unknown.

OBJECTIVE

To examine the association among MMRD, MSI, and survival in patients with resectable gastroesophageal cancer randomized to surgery alone or perioperative epirubicin, cisplatin, and fluorouracil chemotherapy in the Medical Research Council Adjuvant Gastric Infusional Chemotherapy (MAGIC) trial.

DESIGN, SETTING, AND PARTICIPANTS

This secondary post hoc analysis of the MAGIC trial included participants who were treated with surgery alone or perioperative chemotherapy plus surgery for operable gastroesophageal cancer from July 1, 1994, through April 30, 2002. Tumor sections were assessed for expression of the MMR proteins mutL homologue 1, mutS homologue 2, mutS homologue 6, and PMS1 homologue 2. The association among MSI, MMRD, and survival was assessed.

MAIN OUTCOMES AND MEASURES

Interaction between MMRD and MSI status and overall survival (OS).

RESULTS

Of the 503 study participants, MSI results were available for 303 patients (283 with microsatellite stability or low MSI [median age, 62 years; 219 males (77.4%)] and 20 with high MSI [median age, 66 years; 14 males (70.0%)]). A total of 254 patients had MSI and MMR results available. Patients treated with surgery alone who had high MSI or MMRD had a median OS that was not reached (95% CI, 11.5 months to not reached) compared with a median OS among those who had neither high MSI nor MMRD of 20.5 months (95% CI, 16.7-27.8 months; hazard ratio, 0.42; 95% CI, 0.15-1.15; P = .09). In contrast, patients treated with chemotherapy plus surgery who had either high MSI or MMRD had a median OS of 9.6 months (95% CI, 0.1-22.5 months) compared with a median OS among those who were neither high MSI nor MMRD of 19.5 months (95% CI, 15.4-35.2 months; hazard ratio, 2.18; 95% CI, 1.08-4.42; P = .03).

CONCLUSIONS AND RELEVANCE

In the MAGIC trial, MMRD and high MSI were associated with a positive prognostic effect in patients treated with surgery alone and a differentially negative prognostic effect in patients treated with chemotherapy. If independently validated, MSI or MMRD determined by preoperative biopsies could be used to select patients for perioperative chemotherapy.

Genomics of Esophageal Cancer and Biomarkers for Early Detection

In-depth molecular characterization of esophageal oncogenesis has improved over the recent years. Advancement in molecular biology and bioinformatics has led to better understanding of its genomic landscape. More specifically, analysis of its pathogenesis at the genetic level has uncovered the involvement of a number of tumor suppressor genes, cell cycle regulators, and receptor tyrosine kinases. Due to its poor prognosis, the development of clinically applicable biomarkers for diagnosis, progression, and treatment has been the focus of many research studies concentrating on upper gastrointestinal malignancies. As in other cancers, early detection and subsequent intervention of the preneoplastic condition significantly improves patient outcomes. Currently, clinically approved surveillance practices heavily depend on expensive, invasive, and sampling-error-prone endoscopic procedures. There is, therefore, a great demand to establish clearly reliable biomarkers that could identify those patients at higher risk of neoplastic progression and hence would greatly benefit from further monitoring and/or intervention. This chapter will present the most recent advances in the analysis of the esophageal cancer genome serving as basis for biomarker development.

Genetic features of metachronous esophageal cancer developed in Hodgkin's lymphoma or breast cancer long-term survivors: an exploratory study

Background

Development of novel therapeutic drugs and regimens for cancer treatment has led to improvements in patient long-term survival. This success has, however, been accompanied by the increased occurrence of second primary cancers. Indeed, patients who received regional radiotherapy for Hodgkin’s Lymphoma (HL) or breast cancer may develop, many years later, a solid metachronous tumor in the irradiated field. Despite extensive epidemiological studies, little information is available on the genetic changes involved in the pathogenesis of these solid therapy-related neoplasms.

Methods

Using microsatellite markers located in 7 chromosomal regions frequently deleted in sporadic esophageal cancer, we investigated loss of heterozygosity (LOH) and microsatellite instability (MSI) in 46 paired (normal and tumor) samples. Twenty samples were of esophageal carcinoma developed in HL or breast cancer long-term survivors: 14 squamous cell carcinomas (ESCC) and 6 adenocarcinomas (EADC), while 26 samples, used as control, were of sporadic esophageal cancer (15 ESCC and 11 EADC).

Results

We found that, though the overall LOH frequency at the studied chromosomal regions was similar among metachronous and sporadic tumors, the latter exhibited a statistically different higher LOH frequency at 17q21.31 (p = 0.018). By stratifying for tumor histotype we observed that LOH at 3p24.1, 5q11.2 and 9p21.3 were more frequent in ESCC than in EADC suggesting a different role of the genetic determinants located nearby these regions in the development of the two esophageal cancer histotypes.

Conclusions

Altogether, our results strengthen the genetic diversity among ESCC and EADC whether they occurred spontaneously or after therapeutic treatments. The presence of histotype-specific alterations in esophageal carcinoma arisen in HL or breast cancer long-term survivors suggests that their transformation process, though the putative different etiological origin, may retrace sporadic ESCC and EADC carcinogenesis.

The cumulative effects of polymorphisms in the DNA mismatch repair genes and tobacco smoking in oesophageal cancer risk

The DNA mismatch repair (MMR) enzymes repair errors in DNA that occur during normal DNA metabolism or are induced by certain cancer-contributing exposures. We assessed the association between 10 single-nucleotide polymorphisms (SNPs) in 5 MMR genes and oesophageal cancer risk in South Africans. Prior to genotyping, SNPs were selected from the HapMap database, based on their significantly different genotypic distributions between European ancestry populations and four HapMap populations of African origin. In the Mixed Ancestry group, the MSH3 rs26279 G/G versus A/A or A/G genotype was positively associated with cancer (OR = 2.71; 95% CI: 1.34–5.50). Similar associations were observed for PMS1 rs5742938 (GG versus AA or AG: OR = 1.73; 95% CI: 1.07–2.79) and MLH3 rs28756991 (AA or GA versus GG: OR = 2.07; 95% IC: 1.04–4.12). In Black individuals, however, no association between MMR polymorhisms and cancer risk was observed in individual SNP analysis. The interactions between MMR genes were evaluated using the model-based multifactor-dimensionality reduction approach, which showed a significant genetic interaction between SNPs in MSH2, MSH3 and PMS1 genes in Black and Mixed Ancestry subjects, respectively. The data also implies that pathogenesis of common polymorphisms in MMR genes is influenced by exposure to tobacco smoke. In conclusion, our findings suggest that common polymorphisms in MMR genes and/or their combined effects might be involved in the aetiology of oesophageal cancer.

Inflammation and Barrett's carcinogenesis

Barrett's esophagus (BE) is one of the most common premalignant lesions in which normal squamous epithelium of the esophagus is replaced by metaplastic columnar epithelium. Esophageal adenocarcinoma (EA) develops through progression from BE to low- and high-grade dysplasia (LGD/HGD) and to adenocarcinoma. It is widely accepted that inflammation can increase cancer risk, promoting tumor progression. Therefore, inflammation is regarded as the seventh hallmark of cancer. In recent years, the inflammation-cancer connection of Barrett's carcinogenesis has been intensively studied, unraveling genetic abnormalities. Besides genetic alterations, inflammation is also epigenetically linked to loss of protein expression through transcriptional silencing via promoter methylation. Key mediators linking inflammation and Barrett's carcinogenesis include reactive oxygen species (ROS), NFκB, inflammatory cytokines, prostaglandins, and specific microRNAs (miRNAs). Therefore, the decipherment of molecular pathways that contain these and novel inflammatory key mediators is of major importance for diagnosis, therapy, and prognosis. The detailed elucidation of the signaling molecules involved in Barrett's carcinogenesis will be important for the development of pharmaceutical inhibitors. We herein give an overview of the current knowledge of the inflammation-mediated genetic and epigenetic alterations involved in Barrett's carcinogenesis. We highlight the role of oxidative stress and deregulated DNA damage checkpoints besides the NFκB pathway.

Clinical implications of molecular changes in pediatric Barrett's esophagus

Barrett's esophagus (BE) is a preneoplastic condition that predisposes to esophageal adenocarcinoma. Although data on the occurrence of BE in children are limited, recent studies have suggested an increase in the pediatric population. BE is thought to be a complex disease in which individual genetic predisposition interacts with environmental stimuli. Early premalignant clones produce biological and genetic heterogeneity, resulting in stepwise changes in differentiation, proliferation, and apoptosis, allowing disease progression under selective pressure. The value of endoscopic surveillance biopsy for dysplasia and carcinoma in patients with BE is controversial. Thus, the recognition of early and objective alternative risk markers, less susceptible of sampling error, will be of relevance in the management of BE patients. The possibility of performing molecular genetics on paraffin-embedded biopsies will expand our understanding of the natural history of BE and may lead to the use of biomarkers to inform treatment strategies.

Cancerous tissues in forensic genetic analysis

Microsatellites or short tandem repeats (STRs) markers are important tools for mapping disease-causing genes by linkage, for performing investigations in forensic medicine, for population genetic studies and for studying genetic modifications in tumors. In forensic applications neoplastic tissues can be used as a source of genetic information for personal identification or paternity testing when no other specimen is available. Cancer tissues can show microsatellite instability (MSI) and loss of heterozygosity (LOH) also for the STRs used in the forensic field. In this study, we screened 56 sporadic gastrointestinal carcinomas in order to provide further data for the evaluation of the incidence of allelic alterations for 15 STR loci and the suitability of using cancerous tissues in forensic applications. Sixty-six percent of the cancerous tissues were found to possess allelic alterations of the microsatellites analyzed with a high incidence of MSI-L (microsatellite instability low) when compared to the corresponding normal tissue. The most frequently altered loci were D18S51, VWA, and FGA. From a forensic perspective, great care must be taken in evaluating the DNA typing results obtained from cancerous tissue samples.

Investigation of genomic instability in paediatric Barrett's oesophagus using laser microdissection on paraffin-embedded endoscopic biopsies

OBJECTIVES

To investigate the occurrence of microsatellite instability (MSI) in paediatric Barrett's oesophagus (BE) with the aim of identifying a potential marker for patients at risk for developing dysplasia or adenocarcinoma at a later stage.

PATIENTS AND METHODS

Endoscopic oesophageal biopsies from 6 pediatric patients harbouring BE and 6 age-matched controls were retrospectively investigated. After all of the samples were made anonymous, a 5-microm section was cut and stained with toluidine blue. A precise cell was selected and captured using a laser microdissection microscope. Microsatellite analysis was performed on the DNA extracted from the captured cells. Genomic DNA was amplified by polymerase chain reaction using primers for 5 mononucleotide repeats and analysed by GeneMapper software on an ABI 3730. DNA extracted from a formalin-fixed colonic adenocarcinoma known to have MSI was used as a positive control.

RESULTS

The median age of the patients with BE was 9 years. The relevant complaint was long-standing vomiting in 4 cases and history of dysphagia in 3 cases (1 case had both symptoms). All of the cases had a history of reflux oesophagitis with histological confirmation of oesophagitis. Reflux was associated with a hiatus hernia, obesity, and cerebral palsy in each of 3 cases, and with asthma in 2 patients. Histologically, all of the cases showed the presence of specialized intestinal metaplasia containing goblet cells replacing the squamous oesophageal epithelium. None of the cases tested showed any evidence of MSI.

CONCLUSIONS

A single molecular marker that would allow recognition of those patients at risk for Barrett's adenocarcinoma has not yet been identified. The absence of MSI in our cases could be due to the need for a longer period of BE before genomic instability develops, or MSI may only arise in a proportion of patients. This does not exclude other genetic alterations, however rare they may be.

Early genetic instability of both epithelial and stromal cells in esophageal squamous cell carcinomas, contrasted with Barrett's adenocarcinomas

BACKGROUND

We have shown previously that stromal genetic alteration may make a greater contribution to early genesis of ulcerative colitis-associated tumors than sporadic colon cancers. We assessed whether similar differences in genetic alteration might exist between squamous cell carcinomas (SCCs) and Barrett's adenocarcinomas (BACs) of the esophagus.

METHODS

We investigated epithelial and stromal genetic instability with five National Cancer Institute standard (NCI), four chromosome 17 (Chr. 17), and six tumor suppressor gene (TSG) microsatellite markers in 26 SCC and 12 BAC cases and in 11 normal controls, using a novel combination of microdissection, polymerase chain reaction, and GeneScan.

RESULTS

Frequency of epithelial loss of heterozygosity (LOH) increased in the order background mucosa, to precursor lesions, to tumors with both types of carcinoma, especially for the Chr. 17 and TSG markers, while stromal LOH was relatively high but consistent from background mucosa to carcinoma. Epithelial LOH of D17S796 demonstrated a significantly higher frequency in SCCs than in BACs, without significant variation in p53 overexpression. The frequency of microsatellite instability (MSI) showed constant high levels in both epithelium and stroma of background, dysplasia, and carcinomas in the SCC series, and rather low frequencies in the BAC series. Although epithelial hMLH1 and hMSH2 expression decreased with tumor progression, no correlation was found with the individual MSI status.

CONCLUSIONS

Although epithelial LOH exists similarly in both lesion types, whereas epithelial and stromal MSI may occur in a relatively early phase of SCC development, stromal MSI is rare in BACs, strongly suggesting differences in tumorigenesis between the two types.

Promoter methylation of the hMLH1 gene and protein expression of human mutL homolog 1 and human mutS homolog 2 in resected esophageal squamous cell carcinoma

OBJECTIVE

Aberrant expression of mismatch repair genes, such as human mutL homolog 1 (hMLH1) and human mutS homolog 2 (hMSH2), are common in some human cancers, and promoter methylation is believed to inactivate expression of hMLH1. We investigated whether promoter methylation is involved in loss of hMLH1 protein and whether aberrant expression of hMLH1 and hMSH2 protein is related to prognosis after resection for esophageal squamous cell cancer.

METHODS

We analyzed promoter methylation of hMLH1 using methylation-specific polymerase chain reaction and hMLH1 and hMSH2 protein by using immunohistochemistry in 60 resected tumor specimens. The Pearson chi2 test was used to compare expression of hMLH1 and hMSH2 protein among patients with different clinicopathologic parameters. Concordance analysis was performed between hMLH1 methylation and its protein expression.

RESULTS

Loss of hMLH1 and hMSH2 protein was found in 43 (72%) and 39 (65%, P = .06) of 60 resected specimens, respectively. hMLH1 protein correlated well with tumor staging (P < .0001), depth of tumor invasion (P = .008), and nodal involvement (P < .0001) but not with distant metastasis, whereas hMSH2 did not show correlation with any of these parameters. A concordance rate of 83.3% was present between expression of hMLH1 protein and its promoter methylation (P < .001).

CONCLUSIONS

Aberrant expression of hMLH1 and hMSH2 protein is frequently associated with the presence of esophageal squamous cell carcinoma, and expression of hMLH1 protein is a better prognostic predictor than is expression of hMSH2 protein. Promoter methylation is one of the mechanisms responsible for loss of hMLH1 protein in esophageal squamous cell cancer.

Polymorphisms in DNA repair genes in the molecular pathogenesis of esophageal (Barrett) adenocarcinoma

To test the hypothesis that aberrations of DNA repair contribute to susceptibility for the progression of gastroesophageal reflux disease (GERD) into Barrett esophagus (BE) and esophageal adenocarcinoma (EADC), we studied the frequency of polymorphisms of selected DNA repair genes in patients with GERD (n = 126), BE (n = 125) and EADC (n = 56) enrolled in a 2-year prospective case-control study. Controls comprised 95 strictly asymptomatic healthy individuals. Using genomic DNA extracted from blood samples, we identified wild-type and polymorphic variants of XPD (Arg156Arg and Lys751Gln), XRCC1 (Arg194Trp and Arg399Gln) and XRCC3 (Thr241Met), and the poly (AT) insertion/deletion of XPC (PAT). Allelic frequencies were compared between cases and controls using logistic regression to calculate age, gender, smoking and alcohol-adjusted odds ratios (OR) and 95% confidence intervals (CI). Patients with EADC demonstrated a significantly higher frequency of the XPC PAT homozygous variant genotype compared with asymptomatic controls (OR = 3.82; 95% CI = 1.05-13.93). Significantly reduced frequencies were seen for the XPD Lys751Gln homozygous variant genotype in patients with EADC (OR = 0.24; 95% CI = 0.07-0.88), and for the XRCC1 Arg399Gln homozygous variant genotype in patients with BE (OR = 0.38; 95% CI = 0.12-0.64) and GERD (OR = 0.29; 95% CI = 0.12-0.66). We conclude that the malignant phenotype probably results from a summation of polymorphic nucleotide excision repair genes showing opposing effects (an increased risk of XPC versus a protective effect of XPD). The protective effect of the homozygous variant of XRCC1 Arg399Gln for GERD and BE suggests that base excision repair alterations may occur early in progression to EADC, likely in response to GERD-induced endogenous oxidative or inflammatory DNA damage. As GERD and BE are highly prevalent in the general population, this protective effect may well explain why only a fraction of individuals with GERD and BE progress into invasive EADC.

The molecular biology of esophageal adenocarcinoma

BACKGROUND

Barrett's esophagus is an acquired metaplastic change that occurs in the distal esophagus secondary to chronic gastroesophageal reflux. This premalignant condition forms the most important risk factor for developing esophageal adenocarcinoma, which is an extremely aggressive tumor with a 5-year survival rate of less than 25%. Carcinomas that arise in the setting of Barrett's esophagus are thought to develop as part of the metaplasia-dysplasia-carcinoma sequence.

OBJECTIVE

To review the current knowledge on the genomic alterations involved in the development of Barrett's esophagus and its progression to dysplasia and/or cancer.

RESULTS

Several changes in gene structure, gene expression, and protein structure are associated with the progression of Barrett's esophagus to adenocarcinoma. Accumulation of these changes seems to be essential, rather than the exact sequence of these changes. Multiple molecular pathways are involved and interact with each other. Alterations in tumor suppressor genes, amongst which p53 and p16, are early events in the metaplasia-dysplasia-adenocarcinoma sequence, followed by loss of cell cycle checkpoints. Ongoing genomic instability leads to cumulative genetic errors and thereby the generation of multiple clones of transformed cells.

CONCLUSIONS

Within the multistep process of esophageal adenocarcinogenesis, to date no single molecular marker came forward able to predict who will and who will not develop cancer in the setting of Barrett's esophagus. Instead, panels of markers need to be developed in the future allowing to indicate disease progression. Identification of crucial molecular pathways involved in esophageal adenocarcinogenesis would ultimately improve therapy and facilitate development of new treatment strategies.