|Year : 2013 | Volume
| Issue : 1 | Page : 80-83
The significance of mismatch repair genes in gastric cancer
Hye-Jeong Lee1, You-Jin Jang1, Eun-Jung Lee2, Jong-Han Kim1, Sung-Soo Park1, Seong-Heum Park1, Chong-Suk Kim1, Young-Jae Mok1
1 Department of Surgery, Korea University College of Medicine, Seoul, Korea
2 Department of Pathology, Korea University College of Medicine, Seoul, Korea
|Date of Web Publication||10-Apr-2013|
Department of Surgery, Korea University Guro Hospital, Korea University College of Medicine, 80 Guro-dong, Guro-gu, Seoul 152-703
Source of Support: None, Conflict of Interest: None
Background: Microsatellite instability (MSI) is a form of genetic instability characterized by new alleles not present in the normal genotype. This mutation occurs by altered DNA mismatch repair (MMR) genes. Studies of limited numbers of patients have reported conflicting results regarding the association of the MSI phenotype with gastric cancer. This study aims to evaluate the clinical significance of mismatch repair genes in gastric cancer.
Materials and Methods: We studied 156 gastric cancer patients who underwent gastrectomy from March 2010 to February 2011 in our hospital. Mismatch repair status was determined by the immunohistochemical analysis of human MutL Homolog 1 (hMLH1) and human MutS Homolog 2 (hMSH2) expression.
Results: Seventeen (10.9%) cases did not express hMLH1 but all cases expressed hMSH2. In univariate analyses, the expression of hMLH1 was associated with age, nodal status, and Lauren's classification. In multivariate analyses, there was no statistically significant association between the loss of hMLH1 expression and selected clinical parameters.
Conclusion: The expression of hMLH1 was associated with age, nodal status, and Lauren's classification. Our results suggest that MMR gene abnormalities play an important role in the tumorigenesis of patients demonstrating gastric cancer.
Keywords: Human MutL Homolog 1, human MutS Homolog 2, mismatch repair
|How to cite this article:|
Lee HJ, Jang YJ, Lee EJ, Kim JH, Park SS, Park SH, Kim CS, Mok YJ. The significance of mismatch repair genes in gastric cancer
. J Can Res Ther 2013;9:80-3
|How to cite this URL:|
Lee HJ, Jang YJ, Lee EJ, Kim JH, Park SS, Park SH, Kim CS, Mok YJ. The significance of mismatch repair genes in gastric cancer
. J Can Res Ther [serial online] 2013 [cited 2019 Sep 17];9:80-3. Available from: http://www.cancerjournal.net/text.asp?2013/9/1/80/110382
| > Introduction|| |
According to the World Cancer Report, gastric cancer is the fourth most common malignancy and second leading cause of cancer death in the world.  Although human carcinogenesis has been analyzed at the molecular level, the underlying molecular alterations that drive the neoplastic process in gastric cancers are not well understood. 
Recently, it became clear that gastric carcinogenesis is a multifocal, multi-step process requiring sequential alterations in tumor suppressor genes, proto-oncogenes, gate-keeper genes, enzymes, growth factors, and membrane or nuclear receptor.  Among these, mutation carriers of DNA mismatch repair genes exhibit a characteristic phenotype termed microsatellite instability (MSI). 
MSI is a form of genetic instability characterized by new alleles not present in the normal genotype. This type of mutation occurs in a large subset of human tumors and is believed to be caused by altered DNA mismatch repair (MMR) genes.  The frequency of microsatellite instability varies widely among cancers from different organs. In colon cancer, these neoplasms show distinct clinicopathologic characteristics. , Among the MMR genes, the inactivation of human MutS Homolog 2 (hMSH2) and human MutL Homolog 1 (hMLH1) genes are most frequently observed in colorectal carcinomas with MSI.  Regarding gastric cancer, studies of limited numbers of patients have reported conflicting results regarding the association of the MSI phenotype and survival. ,
This study aims to analyze the expression of twomembers of the MMR genes, hMLH1 and hMSH2 and evaluate the clinical significance of MMR genes in gastric cancer.
| > Materials and Methods|| |
We studied 156 gastric cancer patients who underwent gastrectomy after from March 2010 to February 2011 in our hospital. All cases received standard radical gastrectomy with R0. No patients received preoperative chemotherapy or radiotherapy.
The demographic and clinicopathologic variables subjected to analysis were age, gender, tumor size, location, staging and histology. Classification of tumor staging was made according to the TNM/International Union Against Cancer (UICC, 7th edition) system.  Histologic classification was performed according to the World Health Organization (WHO) and Lauren's classification. ,
Mismatch repair status was determined by the immunohisto chemical analysis of hMLH1 and hMSH2 expression. Immunochemical staining of the paraffin sections was performed using a standard streptavidin-biotin method. , The sections were deparaffinized and rehydrated through a graded series of alcohols. After the inhibition of endogenous peroxidase activity by immersion in 3% hydrogen peroxide, antigen retrieval was conducted, with EDTA solution in a microwave.
The sections were incubated overnight with monoclonal antibodies against hMLH1 (ES05, diluted 1:200; Novocastra, UK) and hMSH2 (25D12, diluted 1:200; Novocastra, UK). Thoroughly washed in phosphate-buffered saline (PBS), and then incubated with biotinylated secondary antibody, followed by treatment with a peroxidase kit (DAKO EnVision system). Color was developed by incubating the sections in 0.05% diaminobenzidine about 30 minutes at room temperature. Nuclear counterstaining was accomplished with hematoxylin. The immunohistochemical protein expression of hMSH2 and hMLH1 was evaluated independently by two observers.
The nuclei of normal epithelial cells and lymphocytes are strongly stained for hMLH1 and hMSH2. Lesions were considered negative in the complete absence of detectable nuclear staining in neoplastic epithelial cells. Definite nuclear staining of adjacent nonneoplastic epithelial and stromal cells or lymphocytes served as an internal positive control. Diffuse nuclear staining of these proteins in tumor cells was shown in [Figure 1].
|Figure 1: Immunohistochemical staining of hMLH1 and hMSH2 in gastric cancer. Positive; diffuse nuclear staining (a) and negative; completely absent in all malignant cell (b). hMLH1, human MutL Homolog 1; hMSH2, human MutS Homolog 2|
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Continuous and categorical variables were presented as means ± standard deviation and counts (percentages), respectively. Univariate analysis of continuous variables was performed using the student t test, and of categorical variables using the chi-square test or Fisher exact test, as appropriate. P values were two-sided, and values of < 0.05 were considered statistically significant. Statistically significant variables identified by univariate analyses were entered into the multivariate analyses. SPSS for Windows (ver. 18.0; SPSS Inc., Chicago, IL, USA) was used for the statistical analyses.
| > Results|| |
One hundred fifty-six patients were included in the final analysis, with 109 (70%) men and 47 (30%) women. The mean age was 58.79 ± 11.5 years. Sixty-seven (43%) cases were early gastric cancer and 89 (57%) cases advanced gastric cancer. The type of operation was subtotal gastrectomy in 116 cases (74.4%) and total gastrectomy in 40 cases (25.6%) [Table 1].
Of the 156 cases, 17 cases (10.9%) did not express hMLH1. However, all cases expressed hMSH2 [Table 2].
Results of analyses of the correlation between clinicopathologic features and hMLH1 expression are summarized in [Table 3]. Loss of hMLH1 was associated with old age (P= 0.02), advanced nodal stage (P= 0.047) and intestinal-type gastric cancer (P= 0.042). However, gender, tumor size, tumor location, T stage, distant metastasis, differentiation, lymphatic invasion, and vascular invasion were not associated with loss of hMLH1. And synchronous neoplasm was not associated with loss of hMLH1 expression. In the multivariate analysis, there was no statistically significant association between the loss of hMLH1 expression and selected clinical parameters such as age, nodal stage or intestinal-type [Table 4].
|Table 3: Univariate analysis between clinicopathologic feature and hMLH1 expression|
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| > Discussion|| |
In gastric cancer, the incidence of MSI varies from 15 to 39%.  Although mutations of the hMLH1 or hMSH2 are rare in gastric cancers; hypermethylation of the promoter region of hMLH1 is the major causative event in the development of human cancers with MSI phenotype.  Methylation of the hMLH1 promoter is a frequent event in gastric cancers, and the methylation status correlates well with hMLH1 protein expression. , Consequently, hMLH1 immunohistochemistry may be used as a marker of MSI-high.
There have been many studies demonstrating a defective protein expression of hMLH1 in cases of gastric cancer. The mismatch repair (MMR) deficiency also include cancers associated with hereditary non-polyposis colorectal cancer syndrome (HNPCC). , Recent studies have shown that methylation of the hMLH1 promotor is a frequent event in lung cancers. 
In our study, we have analyzed the expression of twomembers of the MMR gene, hMLH1 and hMSH2, in gastric cancer. The result showed the loss of hMSH1 protein in 17 of 156 (10.9%) cases. The expression of hMSH2 was preserved in all cases. U. Ribeiro Jr, et al reported that the altered hMLH1 immunoexpression occurred in 26.3% of the patients and hMSH2 immunoreactivity was all positive in gastric cancer.  This result suggests that the expression of hMLH1 protein is clinically more significant than hMSH2 protein in gastric cancer.
Regarding the loss of hMLH1 protein, we analyzed the correlation between clinicopathologic features and hMLH1 expression. In several studies, gastric cancers with MSI were associated with specific clinicopathologic characteristics, including older age, distal location, Borrmann gross type II, intestinal subtype, tumor size, lower incidence of lymph node metastasis, lower pTNM stage, and better survival rate. , Univariate analysis of our study showed that loss of hMLH1 was associated with older age (P = 0.02), advanced N stage (P = 0.047) and intestinal-type gastric cancer (P = 0.042). This result is supported by studies that loss of hMLH1 expression by de novo methylation has been shown to be age-related, as older patients present a significantly higher percentage of methylated alleles. , And this result is also supported by other study that the intestinal-type is prevalent in high-risk populations of gastric cancer. 
Studies reported that gastric adenomas and carcinomas in the same individual had the tendency of showing concordant MSI phenotype. , In our study, as shown in [Table 3], there was no significant correlation between synchronous neoplasm of stomach and loss of hMLH1 expression.
Multivariate analyses of our study showed that there was no statistically significant association between loss of hMLH1 and selected clinical parameters. However, multivariate analyses could be tempered by the small sample size in this study. Accordingly, the conclusions in this study should be cautiously interpreted in consideration of small sample size and a further validation study with larger sample size is needed.
Our results suggest that MMR gene abnormalities play an important role in the tumorigenesis of patients demonstrating gastric cancer. The expression of hMLH1 protein is clinically more significant than hMSH2 protein in gastric cancer. The expression of hMLH1 was associated with age, nodal status, and Lauren's classification. Further studies with more cases and long-term follow-up data are needed for better understanding the impact of MMR gene on the outcome.
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[Table 1], [Table 2], [Table 3], [Table 4]