Role of molecular biology in the follow-up of patients who have Barrett's esophagus

Physical activity, obesity and risk for esophageal adenocarcinoma

Over the past three decades, an increasing incidence of esophageal adenocarcinoma (EADC) has been reported throughout North America and Europe at a rate exceeding that of any other human solid tumor. Recent studies have clearly implicated chronic gastroesophageal reflux disease and several lifestyle risk factors, including tobacco consumption, diet and obesity, to be associated with increased risk of EADC. Although physical inactivity is now recognized as a risk factor for several chronic diseases including cancer, only a very limited number of studies have specifically evaluated the association between physical activity and esophageal malignancy. Furthermore, the precise biological mechanisms underlying the association between physical activity, obesity and cancer risk remain unclear. Since successful promotion of healthy body weight and exercise may substantially reduce the future incidence of cancer in the population, the purpose of this review is to explore current evidence linking physical activity, obesity and risk of malignancy – specifically EADC.

Repeated exposure to acid and bile selectively induces colonic phenotype expression in a heterogeneous Barrett's epithelial cell line

Barrett's epithelium is a precancerous, specialized columnar metaplasia in the distal esophagus. We demonstrate the changes in cellular phenotype in a non-neoplastic Barrett's cell line (BAR-T), following exposure to acid and bile salt, the two important components of gastroesophageal refluxate. Cell phenotypes in BAR-T cell line were quantified by fluorescence-activated cell sorting (FACS) using monoclonal antibodies against markers: cytokeratin 8/18 (CK8/18) for columnar, CK4 for squamous, mAbDas-1 for colonic epithelial cell phenotype and p75NTR for esophageal progenitors. Cells were exposed for 5 min each day to 200 microM glycochenodeoxycholic acid at pH 4, pH 6 and pH 7.4 or only to acid (pH 4) for up to 6 weeks. The BAR-T cell line comprised 35+/-5.2% CK8/18, 32+/-3.5% mAbDas-1, 9.5+/-3% CK4 and 4+/-2.5% p75NTR-positive cells. Single exposure to acid and or bile did not change cell phenotypes. However, chronic treatment for at least 2 weeks significantly enhanced (P<0.05) the expression of colonic phenotype and CK8/18-positive cells, as evidenced by FACS analysis. Bile salt at pH 4 and bile salt followed by acid (pH 4) in succession were the strongest stimulators (P<0.01) for induction of colonic phenotype cells. Squamous (CK4(+)) phenotype did not change by the treatments. Cox-2 expression was induced after acute treatment and increased to twofold during chronic treatment, particularly in response to acidic pH. We conclude that BAR-T cells can be utilized as an 'in vitro' model to study the effect of environmental factors and their influence on the cellular phenotype and molecular changes in the pathogenesis of esophageal cancer.

Inducible nitric oxide synthase, nitrotyrosine and p53 mutations in the molecular pathogenesis of Barrett's esophagus and esophageal adenocarcinoma

Nitric oxide (NO) has been implicated as a potential causative factor for endogenous p53 mutations in gastrointestinal malignancy. To investigate the role of NO in esophageal adenocarcinoma (EADC), we studied patterns of p53 mutations, expression of inducible nitric oxide synthase (iNOS) and the tissue accumulation of nitrotyrosine (NTS), a stable reaction product of NO and a marker for cellular protein damage, in human premalignant and malignant esophageal epithelia. Tissues were obtained from patients with gastroesophageal reflux disease (GERD)-induced esophagitis (n = 76), Barrett's esophagus (BE; n = 119) and primary EADC (n = 54). DNA sequencing was used to characterize p53 mutations, RT-PCR to study iNOS mRNA expression, and immunohistochemistry to study NTS. Relative to self-matched normal epithelia, a progressive increase in iNOS mRNA expression was seen in GERD (30%; 23/76), BE (48%; 57/119), and EADC (63%; 34/54) tissues (P < 0.001). Among patients with EADC, elevated levels of NTS immunoreactivity were more frequent in tumors with p53 mutations (11/21; 52%) compared with tumors with wild-type p53 (9/33; 27%; P = 0.063), and specifically in tumors with p53 mutations at CpG dinucleotides (10/12; 83%) compared with non-CpG p53 mutations (1/9; 11%; P = 0.008). The increasing frequency of iNOS (mRNA) overexpression in GERD, BE and EADC supports the hypothesis that an active inflammatory process, most likely a consequence of GERD, underlies molecular progression to EADC. The highly significant association between NTS, reflecting chronic NO-induced cellular protein damage, and endogenous p53 mutations at CpG dinucleotides, provides further evidence for a molecular link between chronic inflammation and esophageal malignancy.

Genetic polymorphisms of microsomal epoxide hydroxylase and glutathione S-transferases M1, T1 and P1, interactions with smoking, and risk for esophageal (Barrett) adenocarcinoma

BACKGROUND

The aim of this case-control study was to test the hypothesis that polymorphisms of the microsomal epoxide hydroxylase (mEH) and glutathione S-transferase (GST) genes modulate the susceptibility to esophageal adenocarcinoma (EADC) associated with smoking.

METHODS

Cases included patients with gastroesophageal reflux disease (GERD) (n=126), Barrett esophagus (BE) (n=125), and EADC (n=56); controls comprised 95 strictly asymptomatic individuals. Genomic DNA was extracted from blood samples, and PCR-based assays were used to genotype mEH (slow allele, fast allele, predicted activity) and GSTM1, GSTT1 and GSTP1. Logistic regression was used to study associations between smoking and genotype, adjusting for age, gender and alcohol consumption.

RESULTS

Relative to asymptomatic controls, no significant differences were found for the distribution of mEH and GST polymorphic variants in cases with GERD, BE or EADC. Smoking was a risk factor for EADC, especially when cigarette exposure was greater than 30 pack-years (adjusted odds ratio [OR] 6.11, 95% confidence interval [CI] 2.2-17.32; P=0.001). The strong association between smoking and EADC was seen preferentially in patients with the active allele of either GSTM1 (OR 7.9, 95% CI 1.14-54.76; P=0.003) or GSTT1 (OR 3.2, 95% CI 1.23-8.35; P=0.004).

CONCLUSIONS

Cigarette smoking is an independent risk factor for EADC, and in particular for heavy smokers. The strong statistical association between smoking and risk for EADC in individuals with the active allele of either GSTM1 or GSTT1 may have potential clinical application in endoscopic surveillance programs to identify individuals with BE at increased risk for progression to EADC.

Obesity and lifestyle risk factors for gastroesophageal reflux disease, Barrett esophagus and esophageal adenocarcinoma

The aim of this study was to examine the association of obesity with esophageal adenocarcinoma, and with the precursor lesions Barrett esophagus and gastroesophageal reflux disease (GERD). This case-control study included cases with GERD (n = 142), Barrett esophagus (n = 130), and esophageal adenocarcinoma (n = 57). Controls comprised 102 asymptomatic individuals. Using logistic regression methods, we compared obesity rates between cases and controls adjusting for differences in age, gender, and lifestyle risk factors. Relative to normal weight, obese individuals were at increased risk for esophageal adenocarcinoma (Odds Ratio [OR] 4.67, 95% Confidence Interval [CI] 1.27-17.9). Diets high in vitamin C were associated with a lower risk for GERD (OR 0.40, 95% CI 0.19-0.87), Barrett esophagus (OR 0.44, 95% CI 0.20-0.98), and esophageal adenocarcinoma (OR 0.21, 95% CI 0.06-0.77). For the more established risk factors, we confirmed that smoking was a significant risk factor for esophageal adenocarcinoma, and that increased liquor consumption was associated with GERD and Barrett esophagus. In light of the current obesity epidemic, esophageal adenocarcinoma incidence rates are expected to continue to increase. Successful promotion of healthy body weight and diets high in vitamin C may substantially reduce the incidence of this disease.

Epidemiology and molecular biology of Barrett esophagus

Over the past three decades, there has been a marked change in the epidemiology of esophageal malignancy, with an increasing incidence of esophageal adenocarcinoma. The reasons for this are largely unknown and remain controversial, but several lifestyle risk factors have been proposed, including gastroesophageal reflux disease (GERD). It is hypothesized that chronic GERD results in acute mucosal injury, promotes cellular proliferation, and induces specialized columnar metaplasia (Barrett esophagus). Progression of Barrett esophagus to invasive adenocarcinoma is reflected histologically by the metaplasia-dysplasia-carcinoma sequence. Dysplasia is widely regarded as the precursor of invasive cancer, and high-grade dysplasia in Barrett epithelium is frequently associated with esophageal adenocarcinoma. Although several molecular alterations have been described in Barrett esophagus, it is anticipated that relatively few will prove to be clinically useful. To date, biomarkers which currently appear to predict the progression of Barrett esophagus to invasive malignancy include aneuploidy, loss of heterozygosity of 17p (implicating the p53 tumor suppressor gene), and cyclin D1 protein overexpression, and with further validation, will most likely be incorporated into routine clinical practice. It is anticipated that models incorporating objective scores of sociodemographic and lifestyle risk factors (ie, age, gender, body mass index), severity of reflux symptoms, endoscopic and histologic findings, and an assessment of a panel of biomarkers will be developed to further define subsets of patients with Barrett esophagus at increased risk for malignant progression, thereby permitting the development of more rational endoscopic surveillance and screening programs.

Cyclin D1 polymorphism (G870A) and risk for esophageal adenocarcinoma

BACKGROUND

To investigate individual susceptibility to gastroesophageal reflux disease, Barrett esophagus, and esophageal adenocarcinoma, the authors studied the frequency of the common G870A polymorphism of CCND1, which encodes cyclin D1, a key cell cycle regulatory protein.

METHODS

The study population included 307 patients who were enrolled in a prospective case-control study to evaluate lifestyle risk factors and molecular alterations in gastroesophageal reflux disease (n = 126 patients), Barrett esophagus (n = 125 patients), and esophageal adenocarcinoma (n = 56 patients). A control group included 95 strictly asymptomatic individuals. Genomic DNA was extracted from cases and controls, and polymerase chain reaction was used to amplify exon 4 of CCND1. After digestion with BsrI, acrylamide gel electrophoresis was used to identify the wild type and common G870A polymorphic alleles. The frequency of alleles (G/G, G/A, A/A) was compared between cases and controls. Immunohistochemistry was used to study cyclin D1 distribution in among patients in the case group.

RESULTS

Compared with the asymptomatic control group, and adjusted for age and gender, increasing frequencies were seen for the A/A genotype in patients with gastroesophageal reflux disease (odds ratio [OR], 2.83; 95% confidence interval [95% CI], 1.09-7.34), Barrett esophagus (OR, 3.69; 95% CI, 1.46-9.29), and esophageal adenocarcinoma (OR, 5.99; 95% CI, 1.86-18.96). No association was seen between genotype and cyclin D1 overexpression.

CONCLUSIONS

The CCND1 A/A genotype was associated with increased risk for gastroesophageal reflux disease, Barrett esophagus, and esophageal adenocarcinoma. The contribution of this polymorphism to susceptibility of defined stages of progression to esophageal adenocarcinoma suggested potential application in endoscopic Barrett surveillance programs.

Gastroesophageal reflux and cancer

The causal relationship between GERD and esophageal adenocarcinoma, although unclear just a few decades ago, now is established fairly well. The physiologic changes and the biocellular alterations of the damaged esophageal mucosa are documented better. Despite this knowledge, the dramatic increase in the incidence of esophageal cancer cannot be explained. The absolute risk of esophageal adenocarcinoma arising from GERD is low, and, at present, does not justify population-screening programs. Still, with the notion that adenocarcinoma of the esophagus is an aggressive cancer once documented, important questions still are in need of answers for patients suffering from reflux symptoms. Patients who have reflux disease are not necessarily symptomatic. It remains unclear if patients experiencing reflux symptoms should undergo mandatory endoscopy with biopsies at the esophagogastric junction. Furthermore, metaplasia of the lower esophagus often is not readily recognizable at endoscopy, and only biopsies can document abnormal histology. A severe and prolonged history of reflux always should orient to the possibility of a reflux-related columnar-lined esophagus. Once documented, Barrett's esophagus needs to be seen as a premalignant condition not necessarily leading to adenocarcinoma formation; despite their increased risk of tumor formation, most patients who have Barrett's esophagus die of other causes. During regular endoscopic follow-up, multilevel circumferential biopsies should document the evolution of the histologic changes in the lower esophagus and at the gastroesophageal junction of these patients. It is the only method available to document the appearance of dysplasia. It still is unclear if medicine or surgery provides the best quality of life and the best protection against the development of dysplasia and the possible progression toward adenocarcinoma formation when intestinal metaplasia is present in the esophagus.

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.

Microsatellite instability in esophageal adenocarcinoma

The frequency of microsatellite instability (MSI), a result of defective mismatch repair during DNA replication, has been reported inconsistently in primary esophageal adenocarcinoma (EADC). Using a panel of 15 markers, the primary aim of this study was to analyze the frequency of MSI in a well-characterized series of 27 primary EADCs, defined according to strict clinicopathologic criteria. Polymerase chain reaction was used to amplify the following microsatellite repeat loci: D2S123, D10S197, D2S119, D11S904, D2S147, D3S1764, D7S1830, D7S1805, D2S434, D9S299, BAT25, BAT26, D5S346, D17S250, and TGF-beta-RII. Tumors were classified as microsatellite-stable (MSS) when no alterations were seen in tumor DNA compared to matched normal tissues, low-level MSI (MSI-L) when 1-5 of 15 markers were altered, and high-level MSI (MSI-H) when more than five markers were altered. Using these stringent criteria, 9/27 (33%) tumors were MSS, 18/27 (67%) tumors were MSI-L, and no tumor was MSI-H. Immunohistochemistry demonstrated cell nuclear expression of DNA mismatch repair proteins (both hMLH1 and hMSH2) in 78% (21/27) of tumors. No associations were seen between MSI and immunohistochemical expression of hMLH1, hMSH2, alterations in p53 or MBD4, tumor grade, pathologic stage, or patient survival. In conclusion, the finding of low levels of MSI in most tumors suggests an inherent baseline genomic instability, and potentially increased susceptibility to mutations during the progression of esophageal adenocarcinoma.

Clinical implications of p53 tumor suppressor gene mutation and protein expression in esophageal adenocarcinomas: results of a ten-year prospective study

OBJECTIVE

This study was undertaken to characterize the spectrum of p53 alterations (mutations and protein expression) in surgically resected esophageal adenocarcinomas, and to correlate molecular alterations with clinicopathologic findings and outcome.

METHODS

Between 1991 and 2001, 91 consecutive patients with esophageal adenocarcinomas underwent subtotal esophagectomy. No patient received induction therapy. Strict clinicopathologic criteria were used to define primary esophageal adenocarcinomas. Genomic DNA was extracted from esophageal tumors, each matched with histologically normal esophageal epithelium (internal control) from the resection margin. Polymerase chain reaction was used to amplify p53 exons 4 through 10. Mutations were studied by single-strand conformation polymorphism analysis and direct DNA sequencing. Immunohistochemical testing (monoclonal antibody DO7) was used to evaluate p53 protein distribution.

RESULTS

Five-year overall survival was 27.3%. No p53 alterations (mutations and/or protein overexpression) were found in normal esophageal epithelium. A total of 57.1% (n = 52) of tumors had p53 alterations (mutations and/or protein overexpression), which on univariate analysis were associated with poor tumor differentiation (P =.001), advanced pTNM stage (P =.009), and number of involved lymph nodes (0, 1-3, >3; P =.04). Patients with p53 alterations had significantly reduced 5-year overall survival relative to patients with wild-type p53 (15% vs 46%; P =.004). The p53 mutations were predominantly G:C to A:T transitions at CpG dinucleotides (52.2%, 24/46)

CONCLUSIONS

We conclude that p53 alterations (mutations and/or protein overexpression) are a predictor of reduced postoperative survival after surgical resection of esophageal adenocarcinomas and that p53 may be a clinically useful molecular marker for stratifying patients in future clinical trials. Patterns of p53 mutations suggest endogenous mutational mechanisms.