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Volume: Barrett's Esophagus
Chapter: Pathophysiology

Are there any molecular markers, including genetic, that occur in Barrett's mucosa prior to histologic dysplasia?

J.D. Mueller (Munich)

On account of its rapidly rising incidence and overall poor prognosis, clinical strategies for the treatment of esophageal adenocarcinoma have increasingly shifted to early detection and treatment. Only a small proportion of the many individuals who have intestinal metaplasia (IM) of the distal esophagus go on to develop a carcinoma [1], and markers that could help select these individuals would obviously be of great value in increasing the effectiveness of Barrett's esophagus surveillance programs. Until now, the best marker has been the histopathologic identification of dysplasia in endoscopic biopsies [2], but the diagnosis of dysplasia is associated a number of difficulties, including inter-observer variation among pathologists [3], and uncertainty as to the precise estimation of subsequent carcinoma development, particularly with low-grade dysplasia (LGD) [4].

In light of these problems, there has been an ever increasing effort to use molecular biology to find a marker that could augment the present histopathologic diagnostic approach by providing more objective and reliable data for risk analysis and prediction. In addition, a long-term goal is the hope that molecular biologic changes might also serve as targets for specific intervention. The following review briefly summarizes a few potential molecular markers that have been identified as being important in the early steps of the metaplasia-dysplasia-carcinoma sequence in Barrett's esophagus.

Cytokeratins, MAbDAS-1

The origin of the metaplastic epithelium in Barrett's esophagus is still not precisely known, but is thought, on the basis of electron microscopic and other studies that show cells with a mixture of squamous and glandular features [5], that a multipotential cell in the esophageal epithelium is responsible. This concept of a hybrid epithelium has also been supported by reports showing that cytokeratin 19 (CK-19) is expressed in stratified squamous epithelium adjacent to areas of Barrett's metaplasia [6], although CK-19 is usually only found in glandular epithelium, and also by the finding of CK-8, 19, and CK-4 and 13 expression by Barrett's epithelium, a mixture of squamous (4 & 13) and glandular cytokeratin types (8 & 19) [7]. A new monoclonal antibody, MAbDAS-1, has also been recently reported to be able to reliably identify areas of Barrett's metaplasia with incomplete IM [8]. Both the cytokeratin profile and the MAbDAS-1 antibody might therefore be a useful adjunct for cases in which the distinction between Barrett's metaplasia and cardia epithelium is not clear histologically.


Barrett's metaplasia is known to occur as a response to chronic reflux esophagitis. Some of the earliest molecular markers showing abnormality in Barrett's esophagus are related to the control of inflammation, cell growth and regeneration. Two examples are inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2), both of which have been found to be elevated in Barrett's metaplasia and dysplasia, as well as in adenocarcinomas of the distal esophagus, indicating that changes in the expression of these molecules are very early events [9]. In addition, increased COX-2 expression has been shown in esophageal cell lines to follow exposure to bile acids [10], a finding that may be a clue to the understanding of the development of metaplasia in response to bile acid reflux.

Telomerase activity

Telomerase activity is necessary for the immortalization of cells during their malignant transformation. One measure of telomerase activity is the expression of telomerase reverse transcriptase catalytic subunit (hTERT). Using quantitative RT-PCR, one study found that hTERT is increased above normal in metaplastic Barrett's epithelium without dysplasia, that it is further increased in dysplastic lesions, and that it reaches very high levels of expression in esophageal adenocarcinoma [11]. Quantitative determination of hTERT expression might serve as a basis for determining the risk of progression of Barrett's esophagus or the potential presence of a carcinoma undetected by endoscopic biopsy.

Proliferation, Ki-67, Aneuploidy

By flow cytometry, it has been found that an increased number of cells in Barrett's metaplasia are in the G1 phase of the cell cycle compared to normal epithelium in which most are in G0 [12]. This is also reflected by an increased Ki-67 labeling index and, by immunohistochemistry, by an increased number of Ki-67 positive cells in the proliferative zone in Barrett's metaplasia [13]. Later, in areas of dysplasia, abnormalities come to be seen in terms of an increased S phase and aneuploidy by flow cytometry [12] and by a elevation and broadening of the proliferative zone so that the Ki-67 positive cells come to occupy the entire thickness of the epithelium [13, 14]. Loss of control over cell proliferation as dysplasia develops in Barrett's epithelium has been related to the accumulation of abnormalities in genes that control the cell cycle.


One of the features used to identify dysplasia in Barrett's metaplasia is loss of polarity of the cells with respect to the gland lumina [15]. One mediator of cell polarity that has been identified in the GI tract is the GTP-binding protein rab11. Interestingly, this protein has been reported by one group to be strongly expressed in LGD in Barrett's esophagus, but only weakly expressed in metaplasia without dysplasia or in high-grade dysplasia and carcinoma [16]. Presumably, increased expression of rab11 is an attempt by the cell to respond to and overcome disturbances in intracellular organization. Failure of this mechanism thus leads to more severe architectural abnormalities characteristic of highgrade dysplasia and carcinoma.


Mutations of p53 have usually been described to be late events, occurring in about 60% of high-grade dysplasia or carcinoma [17-22]. However a few studies have described it to occur in metaplasia or LGD [23]. p53 mutations may be the event that functions as the switch from low to high-grade dysplasia, following an increased S-phase but proceeding aneuploidy [24].

Genetic and chromosomal abnormalities

Various genes and chromosomal regions have been proposed as being important for the development of Barrett's carcinoma. However, most of these are late events that only appear with the onset and progression of carcinoma. Possible exceptions include the FHIT (fragile histidine triad) gene on 3p14.2 which was reported to have frequent mRNA exon deletions in a high percentage of metaplastic lesions as well as carcinomas [25] and the 17q chromosomal region, the site of a presumptive tumor suppressor gene, which has been reported to have an LOH in both carcinoma and matched metaplasia samples over half of the informative cases [26].

At the chromosomal level, comparative genomic hybridization has shown that chromosomal changes can already be identified in metaplastic epithelium (8q, 6p, 10q gains, 13q, Y, 9p losses) and accumulate along the metaplasia-dysplasia-carcinoma sequence [27].

Association of Barrett's esophagus with colonic neoplasia

Earlier reports had described an association between colonic neoplasia and Barrett's esophagus [28], an intriguing concept due to the occurrence of IM in Barrett's esophagus and the expression of intestinal proteins such as Villin [29]. Although a few authors still maintain that such an asociation exists [30], most studies now find that there is no increased incidence of colorectal neoplasia in patients with Barrett's esophagus [31, 32], so that screening based on this concept (e.g. with monoclonal antobodies, etc.) is not warranted.


Until now, most of the molecular biologic changes that have been described in connection with the development of esophageal adenocarcinoma in Barrett's esophagus have been late events. As of yet, no new genes important for the early development of Barrett's esophagus have been definitively identified. However, the increased attention paid to precursor lesions and powerful new methods, such as the microarray technology, should soon provide us with important new insights into the earliest stages of carcinoma development in Barrett's esophagus useful for both improved diagnosis and risk analysis and for therapeutic intervention.


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Publication date: August 2003 OESO©2015