Molecular biology of Barrett's adenocarcinoma.
(65/1038)
OBJECTIVE: To review the current knowledge on the genetic alterations involved in the development and progression of Barrett's esophagus-associated neoplastic lesions. SUMMARY BACKGROUND DATA: Barrett's esophagus (BE) is a premalignant condition in which the normal squamous epithelium of the esophagus is replaced by metaplastic columnar epithelium. BE predisposes patients to the development of esophageal adenocarcinoma. Endoscopic surveillance can detect esophageal adenocarcinomas when they are early and curable, but most of the adenocarcinomas are detected at an advanced stage. Despite advances in multimodal therapy, the prognosis for invasive esophageal adenocarcinoma is poor. A better understanding of the molecular evolution of the Barrett's metaplasia to dysplasia to adenocarcinoma sequence may allow improved diagnosis, therapy, and prognosis. METHODS: The authors reviewed data from the published literature to address what is known about the molecular changes thought to be important in the pathogenesis of BE-associated neoplastic lesions. RESULTS: The progression of Barrett's metaplasia to adenocarcinoma is associated with several changes in gene structure, gene expression, and protein structure. Some of the molecular alterations already showed promise as markers for early cancer detection or prognostication. Among these, alterations in the p53 and p16 genes and cell cycle abnormalities or aneuploidy appear to be the most important and well-characterized molecular changes. However, the exact sequence of events is not known, and probably multiple molecular pathways interact and are involved in the progression of BE to adenocarcinoma. CONCLUSIONS: Further research into the molecular biology of BE-associated adenocarcinoma will enhance our understanding of the genetic events critical for the initiation and progression of Barrett's adenocarcinoma, leading to more effective surveillance and treatment. (+info)
Aggressive acid control: minimizing progression of Barrett's esophagus.
(66/1038)
Barrett's esophagus (BE) is a change in the cellular structure of the lower esophagus believed by many to be caused by frequent acid exposure. The condition is troublesome because of a tendency toward cell proliferation, dysplastic transformation, and cancerous changes within the lesions. It is speculated that the pronounced increase in esophageal adenocarcinoma during the past 25 years may be attributable to acid reflux and associated BE. Strict acid control may cause lesion regression in these patients. However, pH monitoring to confirm adequate acid control is essential, and more than 1 drug may be needed to achieve adequate acid control and manage many patients. More research is needed to determine whether aggressive acid control reduces the dysplasia and cancer risk associated with BE. (+info)
How far to go? Screening and surveillance in Barrett's esophagus.
(67/1038)
There is no dispute that Barrett's esophagus (BE) is associated with an increased risk of esophageal adenocarcinoma. Detecting these cancers early can improve patient survival. But should screening be used to detect BE, or should a surveillance program monitor those already diagnosed with BE for neoplastic changes? Endoscopy and endoscopic biopsy are the only tools available for such screening and surveillance, and the cost effectiveness of either approach must be considered. Two possible solutions are discussed. First, screening could be limited to patients considered at high risk for BE and associated adenocarcinoma. With this approach, more precise risk stratification would be required. The second possible approach is to combine screening for high-risk patients and surveillance for those already diagnosed with BE. Additional outcomes data are needed to determine how often and for what length of time endoscopic surveillance should continue in a patient after several examinations are negative for adenocarcinoma. (+info)
Allelic loss of 10q23, the PTEN tumour suppressor gene locus, in Barrett's oesophagus-associated adenocarcinoma.
(68/1038)
PTEN is a putative tumour suppressor gene located on chromosome band 10q23. Mutations in PTEN have been identified in numerous human malignancies, including cancers of the brain, endometrium, ovary, and prostate. In this study, we screened 80 Barrett's oesophagus-associated adenocarcinomas (BOAd) for loss of heterozygosity (LOH) at 10q23, using the microsatellite markers D10S541, D10S219, and D10S551. Tumours demonstrating LOH were then screened for the presence or absence of PTEN mutations. LOH at one or more loci was identified in 17/80 (21%) cases. In none of these cases did we detect mutations in PTEN. The presence of LOH did not correlate with patient age, tumour stage, degree of differentiation, presence of perineural or vascular invasion, or overall survival. We conclude that LOH at chromosome 10q23 is uncommon in BOAd, is not associated with mutations in the PTEN tumour suppressor gene, and does not correlate with the clinical or pathologic features of these tumours. It is possible that PTEN is inactivated through other mechanisms in BOAd. (+info)
Maximal acid reflux control for Barrett's oesophagus: feasible and effective.
(69/1038)
The treatment of patients with Barrett's oesophagus is controversial. Debate exists regarding the use and value of high dose acid suppression as the standard of practice. Despite prolonged use of high dose proton pump inhibitors (40 mg omeprazole, 60 mg lansoprazole), most studies have shown no convincing evidence of significant regression of Barrett's length. These studies, however, have used fixed doses of proton pump inhibitors and did not regularly document control of oesophageal acid exposure. AIM: To determine whether regression of Barrett's epithelium can be achieved with documented maximal acid suppression. METHODS: We have prospectively followed nine patients with Barrett's oesophagus (eight male; mean age 60 years) for more than 1 year. They were all treated using medical therapy with pH monitoring documenting oesophageal acid exposure over 24 h < 1.6% of the time, and with two or more esophagogastroduodenoscopies performed by the same endoscopist. RESULTS: Acid control was individually tailored and achieved with proton pump inhibitor b.d. (omeprazole 20 mg or lansoprazole 30 mg) and ranitidine at bedtime (HS) (Ran) if necessary. All nine patients (100%) showed some evidence of regression. All nine patients (100%) showed a decrease in Barrett's length (mean 2 cm, range 1-3 cm). Six out of nine (66.67%) patients showed evidence of squamous islands on the last oesophagogastroduodenoscopy. The mean total distal oesophageal acid exposure was 0.38% (range: 0-1.5%). The mean follow-up of patients was 54 months (range: 13-118 months). CONCLUSIONS: Consistent and individually tailored maximal acid suppression documented by pH-metry is achievable and may result in decreased length and development of squamous islands in patients with Barrett's epithelium. This approach should be further evaluated as potentially the preferred medical treatment for these patients. (+info)
Validating clustering for gene expression data.
(70/1038)
MOTIVATION: Many clustering algorithms have been proposed for the analysis of gene expression data, but little guidance is available to help choose among them. We provide a systematic framework for assessing the results of clustering algorithms. Clustering algorithms attempt to partition the genes into groups exhibiting similar patterns of variation in expression level. Our methodology is to apply a clustering algorithm to the data from all but one experimental condition. The remaining condition is used to assess the predictive power of the resulting clusters-meaningful clusters should exhibit less variation in the remaining condition than clusters formed by chance. RESULTS: We successfully applied our methodology to compare six clustering algorithms on four gene expression data sets. We found our quantitative measures of cluster quality to be positively correlated with external standards of cluster quality. (+info)
Genomic alterations in malignant transformation of Barrett's esophagus.
(71/1038)
The incidence of adenocarcinoma in Barrett's esophagus has been increasing rapidly over the past decades. Neoplastic progression is characterized by three well-defined premalignant stages: metaplasia, low-grade dysplasia, and high-grade dysplasia. A genome-wide overview, based on comparative genomic hybridization, was performed, evaluating 30 Barrett's adenocarcinomas and 25 adjacent precursors, i.e., 6 metaplasias, 9 low-grade dysplasias, and 10 high-grade dysplasias. The frequency of losses and gains significantly increased in the subsequent stages of malignant transformation. Losses of 5q21-q23, 9p21, 17p12-13.1, 18q21, and Y were revealed in low-grade dysplasias. This was followed by loss of 7q33-q35 and gains of 7p12-p15, 7q21-q22, and 17q21 in high-grade dysplasias along with high-level amplification (HLA) of 7q21 and 17q21. In the invasive cancers, additional losses of 3p14-p21, 4p, 4q, 8p21, 13q14-q31, 14q24.3-q31, 16q21-q22, and 22q as well as gains of 3q25-q27, 8q23-24.1, 12p11.2-12, 15q22-q24, and 20q11.2-q13.1 were distinguished along with HLAs of 8p12-p22 and 20q11.2-q13.1. Approximately one-third of the alterations in the dysplasias were also found in the adjacent adenocarcinomas, illustrating that multiple clonal lineages can be present in Barrett's esophagus. Novel findings include loss on 7q, gain on 12p, and the observation of several HLAs in high-grade dysplasias. Furthermore, loss of 7q33-q35 was found to represent a significant distinction between low-grade and high-grade dysplasia (P = 0.01), whereas loss of 16q21-q22 and gain of 20q11.2-q13.1 were disclosed to significantly discriminate between high-grade dysplasia and adenocarcinoma (P = 0.02 and P = 0.03, respectively). This inventory of genetic aberrations increases our understanding of malignant transformation in Barrett's esophagus and might provide useful biomarkers for disease progression. (+info)
Allelic loss involving the tumor suppressor genes APC and MCC and expression of the APC protein in the development of dysplasia and carcinoma in Barrett esophagus.
(72/1038)
Samples of Barrett metaplastic specialized epithelium (SE), low-grade dysplasia (LGD), high-grade dysplasia (HGD), and invasive adenocarcinoma (CA) derived from 36 esophagectomy specimens were studied for loss of heterozygosity (LOH) in APC and MCC and for expression of APC protein. Of 18 cases that were heterozygous (informative) for APC, LOH was found in none of 14 SE samples, 2 of 8 LGD samples, 3 of 11 HGD samples, and 5 of 17 CA samples. Immunohistochemically, markedly reduced expression of APC protein (< 50% positive cells) was found in 3 of 19 HGD samples and 4 of 35 CA samples but not in SE or LGD samples. Of 17 cases informative for the MCC gene, LOH was detectable in 1 of 14 SE samples, none of 7 LGD samples, none of 9 HGD samples, and 4 of 16 CA samples. Allelic loss of APC and/or loss of APC protein expression occurs earlier in the metaplasia-dysplasia-carcinoma sequence in Barrett esophagus than LOH in the MCC gene. The determination of alterations at APC or MCC would be of limited importance for the surveillance of patients with Barrett esophagus. (+info)