hMLH1 and hMSH2 expression in human hepatocellular carcinoma

The role of microsatellite instability (MSI) in the pathogenesis of hepatocellular carcinoma (HCC) is incompletely defined. Although high-frequency MSI (MSI-H) is infrequently seen in HCC, some studies have suggested a role for MSI in HCC development. While MSI has been clearly defined for a subset of tumors, in particular colorectal, gastric and endometrial cancers, generally accepted criteria have not been developed for other tumors. Colorectal cancers (CRC) are classified as MSI-H if >30-40% of >5 microsatellite loci analyzed show instability. The MSI-H phenotype is associated with defective DNA mismatch repair (MMR) and is observed in the majority of tumors from patients with hereditary non-polyposis colon cancer (HNPCC) and also in 15% of sporadic CRCs. Inactivating mutations of the hMLH1 or hMSH2 genes lead to defects in MMR in HNPCC. In sporadic CRCs, MMR is usually due to hypermethylation of the hMLH-1 promoter. The role of defective MMR in hepatocellular carcinogenesis is controversial. Immunohistochemistry for hMLH1 and hMSH2 reliably indicates hMLH1 or hMSH2 loss in MSI-H CRC tumors. To investigate the role of defective MMR in HCC carcinogenesis, we performed immunohistochemistry for hMLH1 and hMSH2 on 36 HCCs. BAT26, a microsatellite marker that reliably predicts MSI-H was also examined. All 36 of the tumors stained positively for both hMLH1 and hMSH2, strongly suggesting an absence of either inactivating mutations of hMLH1 and hMSH2 or promoter hypermethylation of hMLH1. None of the tumors showed MSI at the BAT26 locus. These findings suggest that defective MMR does not contribute significantly to hepatocellular carcinogenesis.     

Loss of hMSH2 and hMSH6 expression is frequent in sporadic endometrial carcinomas with microsatellite instability: a population-based study.

Microsatellite instability (MSI) seems to be important in the development of various human cancers including sporadic endometrial cancer. It has previously been shown that alterations in the mismatch repair gene hMLH1 seem to be important for the development of MSI in these tumors. The role of the other mismatch repair genes hMSH2 and hMSH6 has been less well studied, but investigations on patients with hereditary nonpolyposis colorectal cancer indicate that these genes also may be involved. We therefore wanted to investigate the pattern of hMSH2 and hMSH6 expression in a prospective and population-based series of endometrial carcinomas with known hMLH1 expression and MSI status. A total of 138 patients were studied, and pathological staining was seen in 19 cases (14%) for hMLH1, 26 cases (19%) for hMSH2, and 17 cases (12.3%) for hMSH6. Pathological hMLH1 expression was more frequent among tumors with high MSI (those positive for four to five of five markers), whereas pathological expression of hMSH2 and hMSH6 was more frequent among tumors with intermediate MSI (those positive for two to three of five markers). MSI was significantly correlated with pathological expression of hMLH1 (P < 0.001), hMSH2 (P = 0.04), and hMSH6 (P = 0.001). In the group with high MSI, 14 of 16 tumors (88%) showed pathological expression for at least one of the markers. The expression of hMLH1, hMSH2, or hMSH6 did not significantly influence survival. In conclusion, pathological expression of hMLH1 does not seem to account for all tumors with a MSI-positive phenotype in this population-based series of endometrial carcinomas. Our data indicate that the other mismatch repair genes hMSH2 and hMSH6 are also involved, especially in cases with intermediate MSI.     

Microsatellite instability and hMLH1/hMSH2 expression in young endometrial carcinoma patients: associations with family history and histopathology

Endometrial cancer is the second most common malignancy in patients with hereditary nonpolyposis colorectal cancer (HNPCC). The age at diagnosis of HNPCC-associated endometrial cancer is approximately 15 years younger than for sporadic endometrial cancer. Our current study was undertaken to determine the frequency of microsatellite instability (MSI) and absence of hMLH1 or hMSH2 protein expression in young patients with endometrial carcinoma and to correlate these findings with histopathologic and clinical features. Endometrial carcinoma from 62 women (23-52 years, median age 46) were assessed for MSI. Twenty-one of the 62 (34%) tumors demonstrated MSI. Of the 21 tumors demonstrating MSI, 12 showed an absence of hMLH1 expression, 4 showed an absence of hMSH2 expression, and 5 demonstrated normal expression of both proteins. All 41 tumors without MSI demonstrated normal hMLH1 and hMSH2 expression. Two patients with MSI tumors fulfilled the Amsterdam criteria for HNPCC, while 2 had histories suggestive of HNPCC. None of the patients with tumors without MSI had a personal or family cancer history suggestive of HNPCC. The MSI phenotype was associated (p < 0.05) with high FIGO stage and grade, cribriform growth pattern, mucinous differentiation and necrosis. Our findings suggest that the frequency of HNPCC in young endometrial cancer patients is relatively low when compared with the frequency of HNPCC in young colorectal cancer patients. Defects of the MMR proteins hMSH2 or hMLH1 account for MSI in most but not all endometrial cancers from young patients.     

Microsatellite instability and mismatch repair gene inactivation in sporadic pancreatic and colon tumours.

Genomic instability has been proposed as a new mechanism of carcinogenesis involved in hereditary non-polyposis colorectal cancer (HNPCC) and in a large number of sporadic cancers like pancreatic and colon tumours. Mutations in human mismatch repair genes have been found in HNPCC patients, but their involvement in sporadic cancer has not been clarified yet. In this study we screened 21 pancreatic and 23 colorectal sporadic cancers for microsatellite instability by ten and six different microsatellite markers respectively. Microsatellite alterations were observed at one or more loci in 66.6% (14/21) of pancreatic cancers and in 26% (6/23) colon tumours, but all the pancreatic and half of the colon samples showed a low rate of microsatellite instability. All the unstable samples were further analysed for mutations in the hMLH1 and hMSH2 genes and for hypermethylation of the hMLH1 promoter region. Alterations in the hMLH1 gene were found only in colorectal tumours with a large presence of microsatellite instability. None of the pancreatic tumours showed any alteration in the two genes analysed. Our results demonstrate that microsatellite instability is unlikely to play a role in the tumorigenesis of sporadic pancreatic cancers and confirm the presence of mismatch repair gene alterations only in sporadic colon tumours with a highly unstable phenotype.     

Microsatellite instability in inflammatory bowel disease-associated neoplastic lesions is associated with hypermethylation and diminished expression of the DNA mismatch repair gene, hMLH1

Twelve to 15% of sporadic colorectal cancers display defective DNA mismatch repair (MMR), manifested as microsatellite instability (MSI). In this group of cancers, promoter hypermethylation of the MMR gene hMLH1 is strongly associated with, and believed to be the cause of, MSI. A subset of colorectal neoplastic lesions arising in inflammatory bowel disease (IBD) is also characterized by MSI. We wished to determine whether hMLH1 hypermethylation was associated with diminished hMLH1 protein expression and MSI in IBD neoplasms. We studied 148 patients with IBD neoplasms, defined as carcinoma or dysplasia occurring in patients with ulcerative colitis or Crohn's disease. MSI was evaluated using multiplex fluorescent PCR to amplify loci D2S123, BAT-25, BAT-26, D5S346, and D17S250 in all cases. Lesions were characterized as high-frequency MSI (MSI-H) if they manifested instability at two or more loci, low-frequency MSI (MSI-L) if unstable at only one locus, or MS-stable (MSS) if showing no instability at any loci. Methylation-specific PCR was performed to determine the methylation status of the hMLH1 promoter region. hMLH1 protein expression was also evaluated by immunohistochemistry. Thirteen (9%) of 148 neoplasms arising in IBD were MSI-H, comprising 11 carcinomas and 2 dysplastic lesions. Sixteen additional lesions (11%) were MSI-L, comprising 11 carcinomas and 5 dysplastic lesions. The remaining 118 neoplasms (80%) were MSS. Six (46%) of 13 MSI-H, 1 (6%) of 16 MSI-L, and 4 (15%) of 27 MSS lesions showed hMLH1 hypermethylation (P = 0.013). Diminished hMLH1 protein expression in neoplastic cell nuclei relative to surrounding normal cell nuclei was demonstrated immunohistochemically in four of four (100%) hypermethylated lesions tested. In IBD neoplasia, hMLH1 promoter hypermethylation occurs frequently in the setting of MSI, particularly MSI-H. Furthermore, hMLH1 hypermethylation and MSI are strongly associated with diminished hMLH1 protein expression in IBD neoplasms. These findings suggest that hMLH1 hypermethylation causes defective DNA MMR in at least a subset of IBD neoplasms.     

Allelic imbalance at the DNA mismatch repair loci,hMSH2, hMLH1, hPMS1, hPMS2 and hMSH3, in squamous cell carcinoma of the head and neck

BACKGROUND: Squamous cell carcinoma of the head and neck (SCCHN) is one of the 10 most frequently occurring cancers in the world. Defective mismatch repair, as exhibited by the phenomenon of microsatellite instability, has been observed in SCCHN although no reports of mismatch repair gene mutations or altered protein expression have been published. In a variety of microsatellite instability (MSI) positive cancers where mutations in the mismatch repair (MMR) genes were not observed, allelic imbalance at the loci of the MMR genes was prevalent. OBJECTIVE: To investigate whether allelic imbalance at the MMR genetic loci contributes to the development of SCCHN. MATERIALS AND METHODS: 35 matched normal/tumour SCCHN pairs were studied using 29 microsatellite markers located within and adjacent to six known DNA mismatch repair genes. In addition, mutational analysis and protein expression of hMSH2 and hMLH1 were investigated. RESULTS AND CONCLUSIONS: We demonstrated that 36 and 17% of the analysed SCCHN specimens exhibited allele imbalance at the hMLH1 and hMSH3 genetic loci, respectively. Allelic instability at these two loci was found to be correlated with the MSI status of the SCCHN tumours. Allelic instability was found to be uncommon at the other MMR gene loci analysed. One mutation was found in hMSH2 and none in hMLH1 in this series of tumours. 23 of 24 (96%) of the examined SCCHN tumours showed reduced expression of either hMSH2 or hMCH1 genes. Allelic instability in the MMR genes, hMLH1 and hMSH3, is proposed to be involved in the aetiology of SCCHN tumours.     

Microsatellite instability (MSI) and MLH1 and MSH2 protein expression analysis in postmenopausal women with sporadic endometrial cancer

Microsatellite instability (MSI) seems to be important for the development of various human cancers including sporadic endometrial cancer. The aim of this study was evaluation of microsatellite instability in 60 postmenopausal women with endometrial cancer in DNA samples obtained from cancer tissue and blood of the same patients. Control DNA was obtained from normal endometrial tissue (n = 70). MSI was studied at five loci containing single- or dinucleotide repeat sequences and mapping to different chromosomal locations: BAT-25 (at locus 4q12), BAT-26 (2p16), D2S123 (2p16-p21), D5S346 (5q21-q22) and D17S250 (171q11.2-q12). No differences in the MSI frequencies between blood and cancer tissue obtained from patients were detected. The microsatellite instability status was significantly higher in endometrial cancer tissue [21/60 (35%)] compared to control [8/70 (11%)] (p < 0.05). There were significant differences between MSI presence in the subgroups assigned to the histological grades (p < 0.05). The lack of association between MLH1 and MSH2 protein expression and MSI in endometrial cancer samples was observed. The results suggest that the microsatellite instability seems to be important in the development of sporadic endometrial cancer.     

Immunohistochemistry versus microsatellite instability testing in phenotyping colorectal tumors.

PURPOSE: To compare microsatellite instability (MSI) testing with immunohistochemical (IHC) detection of hMLH1 and hMSH2 in colorectal cancer. PATIENTS AND METHODS: Colorectal cancers from 1,144 patients were assessed for DNA mismatch repair deficiency by two methods: MSI testing and IHC detection of hMLH1 and hMSH2 gene products. High-frequency MSI (MSI-H) was defined as more than 30% instability of at least five markers; low-level MSI (MSI-L) was defined as 1% to 29% of loci unstable. RESULTS: Of 1,144 tumors tested, 818 showed intact expression of hMLH1 and hMSH2. Of these, 680 were microsatellite stable (MSS), 27 were MSI-H, and 111 were MSI-L. In all, 228 tumors showed absence of hMLH1 expression and 98 showed absence of hMSH2 expression: all were MSI-H. CONCLUSION: IHC in colorectal tumors for protein products hMLH1 and hMSH2 provides a rapid, cost-effective, sensitive (92.3%), and extremely specific (100%) method for screening for DNA mismatch repair defects. The predictive value of normal IHC for an MSS/MSI-L phenotype was 96.7%, and the predictive value of abnormal IHC was 100% for an MSI-H phenotype. Testing strategies must take into account acceptability of missing some cases of MSI-H tumors if only IHC is performed.     

Not hMSH2 but hMLH1 is frequently silenced by hypermethylation in endometrial cancer but rarely silenced in pancreatic cancer with microsatellite instability

Disruption of the DNA mismatch repair (MMR) system has been found to play an important role in sporadic human cancers of several organs such as colorectum, stomach, endometrium, and pancreas. In cancers of the former three organs, disruption of the MMR system is mainly caused by hypermethylation of the hMLH1 gene. We investigated the expression of the hMLH1 and hMSH2 proteins immunohistochemically in pancreatic and endometrial cancers with high frequency microsatellite instability (MSI-H). Loss of expression of hMLH1 was found in none of seven pancreatic cancer, whereas eight (57%) of 14 endometrial cancer showed loss of expression of hMLH1. On the other hand, one (14%) of seven pancreatic cancers and two (14%) of 14 endometrial cancers showed loss of hMSH2 expression. We further analyzed the methylation status at the promoter region of the hMLH1 and hMSH2 genes and found hypermethylation of hMLH1 at the promoter region in the great majority of endometrial cancers with loss of expression. However, no pancreatic cancer showed hypermethylation. We then further analyzed 22 pancreatic cancer cell lines and obtained similar results. These results suggested that MSI-H in pancreatic cancer is probably caused by different mechanisms from those of other sporadic cancers with MSI-H.     

散发性大肠癌的错配修复缺陷研究

目的探讨错配修复缺陷的散发性大肠癌的临床病理特征及错配修复缺陷检测手段的应用。方法对71例散发性大肠癌行hMLH1启动子甲基化检测、微卫星不稳定检测以及hMLH1和hMSH2的免疫组化检测,分析错配修复缺陷的散发性大肠癌的临床病理特征,探讨三种检测方法的应用价值。结果hMLH1基因启动子甲基化、微卫星不稳定和错配修复蛋白表达的阳性率分别为9.9%,9.9%和71.0%,三者密切相关。hMLH1启动子甲基化和微卫星不稳定的散发性大肠癌均具有结肠癌多发和低分化腺癌相对多见的特征。错配修复蛋白表达阴性的散发性大肠癌仅具有低分化腺癌相对多见的特征。结论错配修复缺陷的散发性大肠癌具有结肠癌和低分化腺癌多发的倾向,hMLH1启动子甲基化和微卫星不稳定以及错配修复蛋白的失表达三者密切相关。     

Methylation of hMLH1 promoter correlates with the gene silencing with a region-specific manner in colorectal cancer

Microsatellite instability is present in over 80% of the hereditary non-polyposis colorectal carcinoma and about 15-20% of the sporadic cancer. Microsatellite instability is caused by the inactivation of the mismatch repair genes, such as primarily hMLH1, hMSH2. To study the mechanisms of the inactivation of mismatch repair genes in colorectal cancers, especially the region-specific methylation of hMLH1 promoter and its correlation with gene expression, we analysed microsatellite instability, expression and methylation of hMLH1 and loss of heterozygosity at hMLH1 locus in these samples. Microsatellite instability was present in 17 of 71 primary tumours of colorectal cancer, including 14 of 39 (36%) mucinous cancer and three of 32 (9%) non-mucinous cancer. Loss of hMLH1 and hMSH2 expression was detected in nine and three of 16 microsatellite instability tumours respectively. Methylation at CpG sites in a proximal region of hMLH1 promoter was detected in seven of nine tumours that showed no hMLH1 expression, while no methylation was present in normal mucosa and tumours which express hMLH1. However, methylation in the distal region was observed in all tissues including normal mucosa and hMLH1 expressing tumours. This observation indicates that methylation of hMLH1 promoter plays an important role in microsatellite instability with a region-specific manner in colorectal cancer. Loss of heterozygosity at hMLH1 locus was present in four of 17 cell lines and 16 of 54 tumours with normal hMLH1 status, while loss of heterozygosity was absent in all nine cell lines and nine tumours with abnormal hMLH1 status (mutation or loss of expression), showing loss of heterozygosity is not frequently involved in the inactivation of hMLH1 gene in sporadic colorectal cancer.     

Methylation of hMLH1 in a population-based series of endometrial carcinomas.

Microsatellite instability (MSI) is a characteristic feature of hereditary nonpolyposis colorectal cancer and is also observed in sporadic colorectal and endometrial cancers. Alterations in the mismatch repair genes hMLH1 and hMSH2 are important for the development of MSI. It has recently been demonstrated that hypermethylation of the hMLH1 promoter region is associated with MSI and appears to be a common mechanism for gene inactivation. For endometrial carcinoma, however, previous studies have been relatively small and have not been population based. We therefore wanted to assess the frequency and prognostic significance of hypermethylation of the hMLH1 and hMSH2 genes in conjunction with hMLH1 protein expression in a prospective and population-based series of endometrial carcinoma patients with known MSI status and complete follow-up. A total of 138 patients were studied, and methylation of hMLH1 was found in 23% of tumors with conclusive results, whereas methylation of hMSH2 was seen in only 1% of tumors. Methylation of hMLH1 was significantly correlated with MSI (P < 0.001). Loss of nuclear staining of hMLH1 protein was seen in 14% of the cases and was significantly correlated with hMLH1 methylation and MSI (P < 0.001). Normal expression of hMLH1 was seen in all of the unmethylated tumors (100%). Of the 14 MSI-positive tumors that were also methylated, all but 1 (93%) showed a loss of nuclear expression of hMLH1. None of the tumors with loss of hMLH1 expression or hMLH1 methylation were aneuploid (P for both < or = 0.05), and loss of hMLH1 expression and hMLH1 methylation was significantly correlated with lack of p53 overexpression (P for both < or = 0.05). Nuclear hMLH1 staining and hMLH1 methylation did not significantly influence survival. In conclusion, hMLH1 methylation was common and was significantly correlated with loss of hMLH1 protein expression, MSI, diploid tumors, and lack of p53 overexpression. In contrast, hMSH2 methylation was infrequent in this prospective and population-based series of endometrial carcinomas.     

Methylation of the hMLH1 promoter in familial gastric cancer with microsatellite instability

Microsatellite instability (MSI), which is recognized as an important mechanism in tumorigenesis, has been reported in familial gastric cancers (FGC). However, genetic defects responsible for this phenotype, that is, mutations in mismatch-repair genes such as hMLH1 and hMSH2, have not been detected in most FGC cases. Earlier studies have shown that the promoter region of the hMLH1 gene was methylated in some sporadic colorectal and endometrial cancers. To determine how FGC acquire MSI, we examined the MSI status, hMLH1-protein expression and methylation status of the hMLH1-promoter region in FGC cases. Out of 9 cancers, 6 from 8 FGC kindreds showed MSI at one or more loci; no germline mutations in the hMLH1 or hMSH2 genes were detected; 4 cancers exhibiting MSI displayed aberrant hMLH1 expression: complete loss in one, decreased level in another, and partially staining pattern in the remaining 2. Methylation in the hMLH1-promoter region was found in these 4 cases. In contrast, the cancers displaying hMLH1-protein expression were not methylated in the hMLH1-promoter region. Our data show a significant association between the absence of hMLH1 expression and methylation of its promoter in FGC cases with MSI. This suggests that the mechanism of inactivation of hMLH1 is epigenetic and that there are other genes responsible for FGC.     

Microsatellite instability and protein expression of the DNA mismatch repair gene, hMLH1, of lung cancer in chromate-exposed workers

Our previous studies of lung cancer in chromate-exposed workers (chromate lung cancer) have revealed that the frequency of replication error (RER) in chromate lung cancer is very high. We examined whether the RER phenotype of chromate lung cancer is due to an abnormality of DNA mismatch repair protein. We investigated the expression of a DNA mismatch repair gene, hMLH1, and hMSH2 proteins using immunohistochemistry and microsatellite instability (MSI) in 35 chromate lung cancers and 26 nonchromate lung cancers. Lung cancer without MSI or with MSI at one locus was defined as "RER(-)," lung cancer with MSI at two loci was defined as "RER(+)," and lung cancer with MSI at three or more loci was defined as "RER(++)." The repression rate of hMLH1 and hMSH2 proteins in chromate lung cancer was significantly more than that of nonchromate lung cancer (hMLH1: 56% vs. 20%, P = 0.006, hMSH2: 74% vs. 23%, P < 0.0001). In chromate lung cancer, the repression rate for hMLH1 was 43% in RER(-), 40% in RER(+), and 90% in the RER(++) group. The repression rate of hMLH1 protein in the RER(++) group was significantly higher than that in the RER(-) and RER(+) groups (P = 0.039). The inactivation of hMLH1 expression strongly correlated with the microsatellite high instability phenotype in chromate lung cancer. The genetic instability of chromate lung cancer is due to the repression of hMLH1 protein.     

Microsatellite instability and hMLH1/hMSH2 expression in Barrett esophagus-associated adenocarcinoma

BACKGROUND: Microsatellite instability (MSI) has been documented in malignancies associated with hereditary nonpolyposis colon carcinoma and in sporadic malignancies of the colon, stomach, and endometrium. In these malignancies, MSI is associated with defects in the DNA mismatch repair enzymes hMSH2 and hMLH1. Defects in these enzymes result in a phenotype characterized by instability of multiple microsatellite repeat sequences throughout the genome. This study sought to determine the prevalence of MSI in 80 primary Barrett esophagus-associated adenocarcinomas (BEAd) and to examine the relation of MSI with the clinical and pathologic features of the tumors. METHODS: Eighty BEAd were evaluated for the presence of MSI by using the microsatellite markers BAT25, BAT26, D10S219, D10S541, and D10S551. These tumors also were evaluated for immunohistochemical expression of hMSH2 and hMLH1. RESULTS: High levels of MSI were not found in any of the tumors examined. Furthermore, immunohistochemical expression of hMSH2 and hMLH1 was retained in all cases evaluated. Evidence of low level MSI was found in 16% of tumors. In none of these tumors, however, was MSI present in more than two of five loci. The presence of MSI did not correlate with patient age, tumor stage, degree of differentiation, or with patient survival. CONCLUSIONS: High level MSI and loss of hMLH1/hMSH2 expression is uncommon in BEAd. A subset of BEAd demonstrate low level MSI. The presence of low level MSI was not associated with the clinicopathologic features of the tumors examined.     

Allelic variation of BAT-25 and BAT-26 mononucleotide repeat loci in tumours from a group of young women with breast cancer

Genomic instability in the form of repeat number variation at microsatellite loci has been reported in several human cancers. To resolve current confusion regarding frequency of microsatellite instability (MSI), standardised protocols have proposed use of a consensus set of informative loci; it is claimed that analysis of 2 apparently quasi-homozygous, quasi-monomorphic, mononucleotide repeats (BAT-25 and BAT-26) is sufficiently accurate to define MSI (obviating need for corresponding constitutive DNA). We examined these loci in 163 breast cancers, 108 of which had previously been analysed at 11-24 other loci and found to have MSI in 38% of them. For BAT-26 only 1/153 (homozygous) tumours showed a contracted allele, with minor size variations (1-6 bp) between individuals. For BAT-25 repeat contractions were unambiguously observed in 12 (7.4%) tumours; only 4 of these were previously designated MSI+. DNA from normal individuals showed significant allelic variation in 8/159 (5%) cases for BAT-25; no instance of heterozygosity was seen for BAT-26. Subsequently, we analysed normal DNA from the 12 individuals whose tumours had MSI at BAT-25; in 2 cases there was germline heterozygosity. We conclude that analysis with BAT-26 (in contrast to other loci) was not a useful detector of MSI. With BAT-25, a low frequency of MSI not much greater than germline polymorphism, also limits the utility of this marker for determining MSI in breast cancer.     

Methylation of the hMLH1 promoter but no hMLH1 mutations in sporadic gastric carcinomas with high-level microsatellite instability

Microsatellite instability (MSI) in tumors from patients with hereditary non-polyposis colorectal cancer (HNPCC) is caused by germline mutations in mismatch repair (MMR) genes, principally hMSH2 and hMLH1. In contrast, somatic mutations in MMR genes are relatively rare in sporadic MSI(+) colon cancers. Rather, the majority of mutation-negative, MSI(+) cases involve hypermethylation of the hMLH1 promoter and subsequent lack of expression of hMLH1. The details of the mechanisms of this epigenetic gene silencing remain to be elucidated. In some colon cancer cell lines, hMLH1 promoter methylation is accompanied by mutation of 1 of the 2 alleles, whereas in other cell lines and tumors, such combinations have not been reported. To contribute to the characterization of MSI in gastric cancer and to directly investigate whether hMLH1 promoter methylation is accompanied by gene mutation in these cancers, we have analyzed 42 gastric tumors and corresponding normal tissue for MSI, hypermethylation of the hMLH1 promoter, and mutations in hMLH1 as well as hMSH2. We found that 10 (23.8%) of 42 cases of sporadic gastric cancer were MSI(+) and that 8 had at least 2 of 12 altered microsatellite loci. All samples with at least 2 altered loci exhibited methylation of the hMLH1 promoter region, but none had detectable mutations in hMLH1 or hMSH2. Our results confirm the importance of methylation of the hMLH1 promoter region in MSI(+) gastric tumors and suggest that methylation takes place in the absence of hMLH1 mutations in these tumors.     

Microsatellite instability in hereditary and sporadic breast cancers

Sporadic cancers and familial breast cancers are characterized by an increase in genetic instability. Little is known about whether mismatch repair defects accompany this genetic instability. We investigated invasive and/or in situ breast cancers from 30 women with deleterious BRCA1/2 mutations and unclassified variant BRCA1/2 alterations. Forty cases of sporadic breast cancers were also investigated, including 7 medullary carcinomas. Malignant and benign lesions were examined from all cases to better understand tumor progression. Automated immunohistochemistry, with antibodies directed against hMLH1 and hMSH2, was used to screen cases for possible mismatch repair defects. When loss of expression was noted, DNA ploidy was performed by cytomorphometry. DNA, after laser microdissection, was extracted from a majority of familial cases and their corresponding controls, and microsatellite instability analysis was performed. None of the familial or sporadic cases had loss of hMSH2 expression. All but one lesion, a DCIS arising in a deleterious BRCA2 mutation carrier, had loss of hMLH1 expression and a tetraploid profile by image cytomorphometry. There was no MSI in any explored lesions (n = 34), as determined by molecular analysis, including the DCIS with loss of hMLH1 expression. We conclude that DNA mismatch repair defects involving hMLH1 and hMSH2 underexpression are extremely rare events in sporadic and familial breast cancer. Mismatch repair gene mutations may be secondary random events in breast cancer progression.     

Simplified MSI marker panel for diagnosis of colorectal cancer

Background: Colorectal cancers (CRCs) tumors are diagnosed by microsatellite instability (MSI) due to accumulation of insertion/deletion mutations in tandem repeats of short DNA motifs (1–6 bp) called microsatellites. Microsatellite instability (MSI) is not only a hallmark marker for screening of hereditary nonpolyposis colorectal cancer (HNPCC), but also a prognostic and predictive marker for sporadic colorectal cancer. Our objective was to determine and study of five mononucleotide microsatellite markers status among Iranian patients with HNPCC and sporadic colorectal cancer. Material and Methods: In the current investigation 80 sporadic CRC and 80 HNPCC patients were evaluated for MSI. The pentaplex panel including 5 quasimonomorphic mononucleotide repeats (NR-21, BAT-26, BAT-25, NR-27 and NR-24) was used. Results: Our findings showed that the NR-21 was the most frequent instable marker among the other markers. 53% and 25.6% specimens had instability in sporadic CRC and HNPCC, respectively. Furthermore, the frequencies of instability BAT-25 was determined in 20% sporadic CRC and 23% HNPCC samples. Interestingly our results demonstrated that the frequency of instability NR-24 was similar 20% sporadic CRC and 20.5% HNPCC. Moreover, percentage of NR-27 in HNPCC was 19.2 and 0% in sporadic CRC. Finally, BAT-26 was instable in 21.8% HNPCC patients while we could find 6.6% instability for BAT-26 in sporadic cases. Conclusion: It seems that among 5 mononucleotides markers NR-21 was the most useful marker for diagnosis HNPCC and sporadic cancer. Following NR-21, BAT-25 and NR-24 are the most reliable markers. Therefore using a triplex panel including 3 aforementioned MSI markers should be more promising markers for identifying MSI status in both patients with HNPCC and/or sporadic colorectal cancer.