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Short Communication |


From the Department of Pathology,*
Josephine
Nefkens Institute, and the Department of
Surgery,
Erasmus University Rotterdam,
Rotterdam; the Rotterdam Esophageal Tumor Study Group, Rotterdam; and
the Laboratory of Cytochemistry and
Cytometry,
Department of Molecular Cell
Biology, Leiden University Medical Center, Leiden, The Netherlands
| Abstract |
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25% of all tumors) was detected, in decreasing order of
frequency, on 5q, 18q, 4q, 3p,
9p, 2q, 11q, 14q, 21q,
4p, 9q, 16q, 1p, and 8p. Frequent gain
(
25% of all tumors) was disclosed, in decreasing order of
frequency, on 20q, 7p, 8q, 1q,
7q, 20p, 17q, 13q, Xp,
6q, 8p, 19q, 5p, 6p, and Xq.
Loss of the Y chromosome was found in 60% of male cases. High level
amplification was frequently (>10% of all tumors) detected on
7q21, 8p22, 12p11.2, 17q12-q21, and
19q13.1-q13.2. The precursor lesions showed multiple aberrations
in all high-grade dysplasias, whereas few genetic changes were
discerned in LGD and metaplasias. High level amplifications were also
found in high-grade dysplasias, ie, on 7q21,
8p22, and 17q12-q21. Moreover, the percentage of
aberrations was not significantly different for invasive carcinomas or
high-grade dysplasias. Approximately 70% of the precursor aberrations
were also present in the adjacent carcinoma. Minimal overlapping
regions in the preneoplasias included loss on 18q12-q21 and gains on
8q23 and 17q12-q21, suggesting involvement of genes residing in
these regions. In conclusion, we have (i) created a map of
genetic alterations in gastric cardia adenocarcinomas and (ii) provided
evidence for the presence of a metaplasia-dysplasia-carcinoma sequence
in this poorly understood type of cancer.
| Introduction |
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Cytogenetic studies of series of both gastric and esophageal adenocarcinomas have shown frequent chromosomal rearrangement of 11p131514 and deletion of 3q.15 In a study of 37 adenocarcinomas in Barretts esophagus and gastric cardia, loss of the Y chromosome appeared to be a prominent feature.16 Further, rearrangements were most frequently seen of chromosome arms 1p, 3q, 11p, and 22q. Genetic abnormalities have been extensively documented in the formerly common pyloric-antrum type of gastric cancer. Patterns of gene amplification have been investigated.17 Ranzani et al18 detected loss of heterozygosity (LOH) at 5q, 11p, 17p, and 18q, and with a low frequency also at 7q and 13q. In these gastric cancers deletions often occur at the APC and MCC loci on 5q21.19 Little is known of LOH in gastric cardia tumors. In a study of adenocarcinoma of the gastric cardia frequent allelic loss was seen on 3p, 4q, 5q, 8p, 9pq, 12q, 13q, 17p, and 18q.20 A comparison of esophageal and gastric cardia cancers revealed similar patterns of TP53 alterations.21 Comparative genomic hybridization of gastro-esophageal junction cancers was reported including limited numbers of gastric cardia carcinomas.22-24 Gain of chromosome 20 was most frequently found. Further, prominent gain was seen on 1q, 7pq, 8q, 13q, 15q, and 17q, and loss was observed on 4pq, 5q, 9p, 14q, and 18q. Recurrent high-level amplifications were disclosed at 8q2324.1, 17q1221, and 19q13.1.
In this study we wanted to document the spectrum of genetic changes in a series of gastric cardia adenocarcinomas and surrounding preneoplastic lesions. We were especially interested in a metaplasia-dysplasia-carcinoma sequence in this type of cancer. Therefore, we collected metaplastic and dysplastic tissues from archival resection specimens of gastric cardia adenocarcinomas. To our knowledge such an investigation has not been reported. Comparative genomic hybridization (CGH) was used to obtain a genome-wide view of chromosomal gains and losses.
| Materials and Methods |
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We collected 20 surgical specimens with adenocarcinomas of the gastric cardia, ie, the center of the tumor was clearly located in the proximal stomach. Barretts epithelium was absent in all cases. The presence of Helicobacter pylori infection was evaluated on routine H&E sections, but in difficult cases special stains were used. Special attention was given to the selection of preneoplastic lesions (metaplasia, dysplasia) in the vicinity of the tumor. Intestinal metaplasia was defined as the presence of goblet cells in gastric epithelium. Precursors were selected from 10 resection specimens. In the other 10 cases no preneoplasias could be found, possibly due to overgrowth of these generally large cancers. Fourteen of the tumor specimens were derived from paraffin-embedded, formalin-fixed, materials; six were fresh-frozen. All preneoplastic lesions were paraffin-embedded. Staging of the tumors was performed according to the Union Internationale Contre le Cancer (UICC).25
Comparative Genomic Hybridization
Isolation of DNA from the formalin-fixed, paraffin-embedded tumor material was performed using standard procedures. Microdissection of the tumor areas was performed using a hollow bore coupled to the microscope. Metaplastic and dysplastic areas were scraped from 10-µm paraffin sections using a stereo microscope and a 0.4 x 12 mm hollow needle. DNA from both fresh-frozen and archival paraffin samples was isolated according to standard protocols, and concentration, purity, and molecular weight of the DNA were estimated. Tumor DNA with a fragment size of <1 kb was labeled with a platinum/biotin complex (bio-ULS), using the ULS biotin labeling kit (Kreatech Diagnostics, Amsterdam, The Netherlands.)26 Tumor DNA with larger DNA fragment sizes was labeled with biotin by nick translation (Nick Translation System, Gibco BRL, Gaithersburg, MD). Likewise, male reference DNA (Promega, Madison, WI) was labeled by nick translation with digoxigenin (Boehringer Mannheim, Indianapolis, IN). The reaction time and the amount of DNase were adjusted to obtain a matching probe size for reference and tumor DNAs. Molecular weight of both tumor and reference DNA was checked by gel electrophoresis after nick translation, and ranged between 500 and 1500.
CGH was performed as described before.24,26 In brief, 400 ng of labeled archival tumor DNA, 200 ng of reference DNA, and 15 µg of unlabeled Cot-1 DNA were ethanol-precipitated and dissolved in 10 µl of hybridization mixture (50% formamide, 0.1% Tween-20, and 10% dextran sulfate in 2x standard saline citrate at pH 7.0). The probe mixture was denatured and hybridized to normal male metaphase chromosomes (Vysis, Downers Grove, IL) for 3 days at 37°C. After washing of the slides, fluorescent detection of the biotin- and digoxigenin-labeled DNA probes was accomplished with avidin-fluorescein isothiocyanate and anti-digoxigenin rhodamine, respectively. Samples were counterstained with 4',6'-diamidino-2-phenyl indole (DAPI) in anti-fade solution.
Images were acquired with an epifluorescent microscope (Leica DM, Rijswijk, The Netherlands) equipped with a CCD camera (Photometrics, Tucson, AZ), three single excitation filters, a multiband pass dichroic mirror, and emission filters. For comparative genomic hybridization analysis Quips XL software (version 3.1.1; Vysis) was used. Loss of DNA sequences was defined as chromosomal regions where the mean green to red ratio was <0.85, whereas gain was defined as chromosomal regions where the ratio was >1.15. These threshold values were based on series of normal controls. A high-level amplification, probably representing an amplicon, was seen as a distinct peak (ratio >1.5). At least 8 to 10 metaphases per sample were used for the analysis of gains and losses.
| Results |
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We have used CGH to obtain a genome-wide overview of 20 archival
gastric cardia adenocarcinomas (17 males, 3 females) and 10 adjacent
preneoplastic lesions: 4 metaplasias, 1 low-grade dysplasia (LGD), and
5 high-grade dysplasias (HGD; see Table 1
). Intestinal metaplasia was found in
the vicinity of 6 tumors (30%), whereas H.
pylori-associated gastritis was present in 3 cases (15%).
Multiple genetic alterations were discriminated in all adenocarcinomas
(Figure 1A)
. Frequent loss (
25% of all
tumors) was detected, in decreasing order of frequency, on 5q (55%),
18q (55%), 4q (50%), 3p (45%), 9p (45%), 2q (40%), 11q (35%), 14q
(35%), 21q (35%), 4p (30%), 9q (30%), 16q (30%), 1p (25%), and 8p
(25%). Frequent gain (
25% of all tumors) was disclosed, in
decreasing order of frequency, on 20q (80%), 7p (70%), 8q (60%), 1q
(55%), 7q (55%), 20p (45%), 17q (40%), 13q (35%), Xp (35%), 6q
(30%), 8p (30%), 19q (30%), 5p (25%), 6p (25%), and Xq (25%).
Loss of the Y chromosome was found in 60% of male cases. Minimal
overlapping regions for loss were assigned to 3p14, 5q21, 5q31-q33,
8p21-p22, 9p21, 11q24-q25, 14q23-q24, 18q12-q21, and 21q21, whereas
minimal overlapping regions for gain were assigned to 1q41-q42,
7p12-p14, 7q21, 8p22, 8q21.3-q23, 12p11.2, 13q12-q14, 17q12-q21,
19q13.1-q13.2, and 20q11.2-q13.1. Recurrent (>10% of all tumors)
high-level amplification (HLA) was detected on 7q21, 8p22, 12p11.2,
17q12-q21, and 19q13.1-q13.2, illustrating the genomic instability in
these carcinomas.
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The precursor lesions showed multiple aberrations in all HGDs,
whereas few genetic (mostly non-frequent) changes were discerned in LGD
and metaplasias (Figure 1B)
. Frequent gains included 8q (40%), 6p
(30%), 7q (30%), 13q (30%), 17q (30%), and 20q (30%), whereas
frequent losses were seen on 18q (50%), Y (40%), 2q (30%), 4p
(30%), 5q (30%), 9p (30%), and 21q (30%). HLAs were found only in
HGD: two on 17q12-q21, one on 7q21, and one on 8p22. The mean
percentage of aberrations in the 20 adenocarcinomas appeared only
slightly higher than in the 6 dysplasias (11.9 vs. 10.6,
respectively). This was caused by the 5 HGDs in this set of dysplasias
(Table 2)
. The 4 metaplasias showed an
average of 0.7 alterations per lesion. Approximately 70% of the
precursor aberrations were also present in the adjacent carcinoma,
illustrating the presence of a metaplasia-dysplasia-adenocarcinoma
sequence in gastric cardia cancer (Table 2
and Figure 2
). A high percentage of concurrent
alterations were seen in HGD and invasive cancer, despite the evident
differences in histomorphology (Figure 2, CF)
. Overlapping
alterations were not only seen in HGD, but also in LGD (case 2), and
even in intestinal metaplasia (cases 3 and 10). Minimal overlapping
regions in the preneoplasias included loss on 18q12-q21 and gains on
8q23 and 17q12-q21, suggesting involvement of genes in these regions in
the development of cancer of the proximal stomach.
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| Discussion |
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We have disclosed frequent alterations in gastric cardia cancers and precursors, and minimal overlapping regions could be assigned at multiple locations. Below we will discuss the most prevalent and relevant candidate genes for these frequent chromosomal regions of gain or loss in the adenocarcinomas28,29 (also listed on the genecards database of the Weizmann Institute at http://bioinfo.weizmann.ac.il/cards).
Chromosomal Loss
In the literature only one detailed study has been reported
describing LOH solely in gastric cardia adenocarcinomas.20
Recurrent allelic losses (>50%) were seen on 3p, 4q, 5q, 8p, 9p, 9q,
12q, 13q, 17p, and 18q. In our series the most frequent losses were
noted on chromosome arms 5q and 18q (both 55% of cases), whereas less
frequent deletions were found on 1p, 2q, 3p, 4p, 4q, 8p, 9p, 9q, 11q,
14q, 16q, and 21q. Thus, a good concordance is present between these
two studies using different methodologies. A discrepancy between the
two series is our low percentage of deletions on distal 17p within the
TP53 (tumor protein p53) region. It might be attributed to the lower
sensitivity of CGH, as compared to LOH analysis.30
Furthermore, the frequency of TP53 alterations might be somewhat lower
in gastric cardia cancers than in esophageal (Barretts)
adenocarcinomas.31
The determination of two regions of
loss on 5q might point to two sites for putative tumor suppressors. The
5q21 region contains the mutated in colorectal cancer (MCC) and
adenomatous polyposis coli (APC) genes, which have been shown to be
involved in Barrett-related cancers. The loss at 5q31-q33 might involve
-catenin (CTNNA1, locus at 5q31), which is part of the
E-cadherin-catenin complex. The loss at 18q12-q21 might be related to
DCC (deleted in colorectal carcinoma) and/or DPC4 (deleted in
pancreatic carcinoma), genes known to be altered in gastrointestinal
cancers. A high frequency of loss is observed on chromosome 4, but it
was not possible to assign a common region on each of the two
chromosome arms. This could be due to a high density of tumor
suppressor genes on this chromosome, which is in concordance with a LOH
study of chromosome 4q in Barretts adenocarcinoma.32
Chromosomal Gain
The most prominent gain was found on chromosome 20, especially 20q (80%), with a minimal region at 20q11.2-q13.1. HLA was detected on 20q13.1. It is noteworthy that in a recent CGH array investigation of breast carcinomas, CYP24, encoding vitamin D24 hydroxylase, and located at 20q13.2, was discriminated as a putative oncogene.33 High-frequency gain was also noted on 8q with a minimally gained region at 8q21.3-q23, which is slightly proximal to the MYC (v-myc myelocytomatosis oncogene) locus. Expression studies have shown that, eg, epidermal growth factor receptor, Kirsten rat sarcoma viral oncogene homologue, or v-erb-b2 oncogene (HER2-neu) are involved in the malignant transformation of Barretts esophagus,34 which may explain the gains and amplifications at 7p12-p14, 12p11.2, and 17q12-q21. The amplification on 7q21 is associated more with hepatocyte growth factor (HGF) than with the more distally located MET oncogene, encoding for the HGF receptor. HGF serum levels were reported to correlate significantly with the aggressiveness of gastric carcinomas.35 Immunohistochemistry showed that MET was overexpressed in about half of gastric cancers, whereas gene amplification was detected by Southern blot hybridization in about 10% of them.36 The recurrent HLA at 8p might be associated with cathepsin B, which appears to be amplified and overexpressed in Barrett-related carcinomas.37 HLA at 19q13.1-q13.2 might involve cyclin E, which has recently been described as the candidate gene of a 19q12 amplicon in adenocarcinomas of the gastro-esophageal junction.38
The genetic spectrum of imbalances in gastric cardia cancers, disclosed by CGH, is very similar to the distribution of alterations seen in Barrett-related adenocarcinomas.24,39 It is also in keeping with allelotyping and in situ hybridization studies of esophageal adenocarcinoma.40-42 Furthermore, the pattern of gains and losses in the preneoplastic lesions shows a high degree of similarity to the genetic changes seen in Barretts esophagus 39,43-46 , ie, losses in cardia cancer precursor lesions are frequently seen on 4p, 5q, 9p, and 18q, whereas gains are repeatedly found on 7q, 8q, 17q, and 20q. This illustrates, moreover, that adenocarcinomas at these two locations have much in common, although a minor proportion of proximal stomach cancers might be related to H. pylori infection. However, our data strongly suggest a shared etiology of gastro-esophageal junction adenocarcinomas arising either in the distal esophagus (Barretts esophagus) or in the gastric cardia.
| Footnotes |
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Supported by Dutch Cancer Society grants EUR 971478 and EUR 971404.
Accepted for publication March 8, 2001.
| References |
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