Original articlesRecurrent chromosome changes in 62 primary gastric carcinomas detected by comparative genomic hybridization
Introduction
Gastric cancer is considered to be the second most common cancer worldwide [1], affecting approximately 24,000 persons in the United States in 1994 [2]. The prognosis for gastric adenocarcinoma is very poor, with 5-year survival rates ranging from 5% to 20% [3]. The development of new diagnostic, preventive, and treatment approaches requires a good understanding of the mechanisms of the complex multistep process of tumorigenesis in the gastric cancer. Although several studies have been performed to study the relationship between gastric cancer and known oncogenes and tumor suppressors (e.g., amplification of ERBB-2 [4], K-SAM [5], and C-MET [6], mutations of the TP53 [7], and APC [8] genes], very little information is available detailing recurring chromosome alterations in gastric cancer because of the difficulties in karyotype analysis with conventional chromosome banding techniques.
Comparative genomic hybridization (CGH) is an approach to analyze the entire genome for regional variations of DNA sequence copy number (gain, loss, and amplification of DNA sequences) in a single experiment [9]. In CGH, equal amounts of total genomic DNA from a tumor sample and a normal control tissue are labeled with green or red fluorochromes and simultaneously hybridized to normal metaphase chromosomes. After hybridization, the fluorescence ratio between tumor and normal DNA along each reference chromosome is measured and analyzed. This technique can detect recurrent copy number changes and may highlight chromosomal regions containing genes that contribute to cancer development and/or progression. Since it was developed, CGH has been applied to study genetic alteration in many solid tumors including gastric cancer 10, 11, 12. This report using CGH examines 69 primary gastric carcinomas with several recurring chromosomal alterations that include the gain of 3q, 8q, 13q, 20q, and the loss of 1p, 17p, and 19p. Gain of 20q and loss of 19p were confirmed by interphase fluorescence in situ hybridization (FISH) using corresponding bacterial artificial chromosomes (BAC) clones.
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Primary tumor specimens and DNA extraction
All 69 cases in this study were untreated patients from whom primary tumor tissue was collected at the time of surgical resection at the Department of Surgery, Harbin Medical University (Harbin, China), Cancer Hospital, Sun Yat-Sen University of Medical Science (Guangzhou, China), and the Department of Surgery, Norman Bethune Medical University (Changchun, China). The clinical and histopathologic data are summarized in Table 1. Tumor tissue was selected by histopathologic examination on the
Comparative genomic hybridization analysis
Comparative genomic hybridization analysis was carried out on 69 cases of primary gastric cancers. Of 69 cases, 62 showed chromosome imbalances. Three histopathologic subtypes of gastric cancer were analyzed in this study, including adenocarcinoma (44 cases), signet-ring carcinoma (9 cases), and mucin-producing adenocarcinoma (9 cases). All changes in DNA sequence copy number for the entire genome detected in these 62 primary gastric cancers are listed in Table 1 and summarized in Fig. 1. Fig. 2
Discussion
In the present study, 62 primary gastric cancers were analyzed by comparative genomic hybridization. The findings in this study are in general agreement with previous LOH and CGH results. For example, gain of 8q, 20q, and loss of 1p, 17p, and 19p have been detected as frequent chromosomal alterations in gastric cancer in at least one of the previous CGH studies 10, 11, 12.
Over-representation of 8q and 20q was the most prominent feature in this study. Gain of 8q was detected in 31/62 cases
Acknowledgements
This study is supported in part by the Leung Kwok Tze Foundation and by a Chinese National Outstading Young Scientist Award (No. 39825511).
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These authors contributed equally to this work.