PubMed Health⌕ Search

SEARCH · PubMed Health

Results for “DNA MICROSATELLITE INSTABILITY”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 217 records · Page 12Linked to original sources
PubMed1999

BAT-26 and BAT-40 instability in colorectal adenomas and carcinomas and germline polymorphisms.

Analysis of the mononucleotide repeats BAT-26 and BAT-40 has reportedly revealed significant microsatellite instability in sporadic colorectal adenomas, whereas studies with dinucleotide and tetranucleotide repeats have not. In addition, BAT-26 has been reported to be "quasimonomorphic" in the germline. We evaluated BAT-26 and BAT-40 in a series of colorectal tumors previously analyzed with a panel of tetranucleotide repeats. Instability in BAT-26 or BAT-40 was significantly associated with tetranucleotide repeat instability in sporadic adenomas and carcinomas (P < 0.0001) and was similarly much less common in adenomas than in carcinomas. Germline polymorphisms in both BAT-40 and BAT-26 were identified, and the frequency of BAT-26 polymorphisms was significantly higher in African Americans than in Caucasians (7.7% versus 0.08%, P < 0.001). BAT-26 and BAT-40 may be very useful in evaluating instability in small tumors, as sufficient DNA to be amplified by large panels of microsatellites is not always available from such lesions. Polymorphisms in these microsatellites, however, limit their utility in determinations of microsatellite instability without corresponding normal DNA.

3-Hydroxysteroid Dehydrogenases↗
PubMed2001

Hypermethylation of the hMLH1 gene promoter is associated with microsatellite instability in early human gastric neoplasia.

A significant portion of gastric cancers exhibit defective DNA mismatch repair, manifested as microsatellite instability (MSI). High-frequency MSI (MSI-H) is associated with hypermethylation of the human mut-L homologue 1 (hMLH1) mismatch repair gene promoter and diminished hMLH1 expression in advanced gastric cancers. However, the relationship between MSI and hMLH1 hypermethylation has not been studied in early gastric neoplasms. We therefore investigated hMLH1 hypermethylation, hMLH1 expression and MSI in a group of early gastric cancers and gastric adenomas. Sixty-four early gastric neoplasms were evaluated, comprising 28 adenomas, 18 mucosal carcinomas, and 18 carcinomas with superficial submucosal invasion but clear margins. MSI was evaluated using multiplex fluorescent PCR to amplify loci D2S123, D5S346, D17S250, BAT 25 and BAT 26. Methylation-specific PCR was performed to determine the methylation status of hMLH1. In two hypermethylated MSI-H cancers, hMLH1 protein expression was also evaluated by immunohistochemistry. Six of sixty-four early gastric lesions were MSI-H, comprising 1 adenoma, 4 mucosal carcinomas, and 1 carcinoma with superficial submucosal invasion. Two lesions (one adenoma and one mucosal carcinoma) demonstrated low-frequency MSI (MSI-L). The remaining 56 neoplasms were MSI-stable (MSI-S). Six of six MSI-H, one of two MSI-L, and none of thirty MSI-S lesions showed hMLH1 hypermethylation (P<0.001). Diminished hMLH1 protein expression was demonstrated by immunohistochemistry in two of two MSI-H hypermethylated lesions. hMLH1 promoter hypermethylation is significantly associated with MSI and diminished hMLH1 expression in early gastric neoplasms. MSI and hypermethylation-associated inactivation of hMLH1 are more prevalent in early gastric cancers than in gastric adenomas. Thus, hypermethylation-associated inactivation of the hMLH1 gene can occur early in gastric carcinogenesis.

Adaptor Proteins, Signal Transducing↗
PubMed2005

Post-transplant lymphoproliferative disorders: molecular basis of disease histogenesis and pathogenesis.

Post-transplant lymphoproliferative disorders (PTLD) represent a serious complication of solid organ and allogeneic bone marrow transplantation. PTLD generally display B-cell lineage derivation, involvement of extranodal sites, aggressive histology and clinical behaviour, and frequent association with EBV infection. The occurrence of IgV mutations in the overwhelming majority of PTLD documents that malignant transformation targets germinal centre (GC) B-cells and their descendants both in EBV-positive and EBV-negative cases. Analysis of phenotypic markers of B-cell histogenesis, namely BCL6, MUM-1 and CD138, allows further distinction of PTLD histogenetic categories. PTLD expressing the BCL6(+)/MUM1(+/-)/CD138(-) profile reflect B-cells actively experiencing the GC reaction and comprise diffuse large B-cell lymphoma (DLBCL) centroblastic and Burkitt lymphoma. PTLD expressing the BCL6(-)/MUM1(+)/CD138(-) phenotype putatively derive from B-cells that have concluded the GC reaction and comprise the majority of polymorphic PTLD and a fraction of DLBCL. A third group of PTLD is reminiscent of post-GC and pre- terminally differentiated B-cells that show the BCL6(-)/MUM1(+)/CD138(+) phenotype and are morphologically represented by either polymorphic PTLD or DLBCL immunoblastic. The molecular pathogenesis of PTLD involves infection by oncogenic viruses, namely Epstein-Barr virus, as well as genetic or epigenetic alterations of several cellular genes. At variance with lymphoma arising in immunocompetent hosts, whose genome is relatively stable, a fraction of PTLD are characterized by microsatellite instability as a consequence of defects in the DNA mismatch repair mechanism. Apart from microsatellite instability, molecular alterations of cellular genes recognized in PTLD include alterations of c-MYC, BCL-6, p53, DNA hypermethylation, and aberrant somatic hypermutation of proto-oncogenes.

B-Lymphocytes↗
PubMed1999

The cellular basis of the efficacy of the trinuclear platinum complex BBR 3464 against cisplatin-resistant cells.

Multinuclear platinum compounds have been designed to circumvent the cellular resistance to conventional mononuclear platinum-based drugs. In this study we performed a comparative study of cisplatin and of the triplatinum complex BBR 3464 in a human osteosarcoma cell system (U2-OS) including an in vitro selected cisplatin-resistant subline (U2-OS/Pt). BBR 3464 was extremely potent in comparison with cisplatin in U2-OS cells and completely overcame resistance of U2-OS/Pt cells. In both cell lines, BBR 3464 accumulation and DNA-bound platinum were higher than those observed for cisplatin. On the contrary, a low frequency of interstrand cross-links after exposure to BBR 3464 was found. Differently from the increase of DNA lesions induced by cisplatin, kinetics studies indicated a low persistence of interstrand cross-link formation for BBR 3464. Western blot analysis of DNA mismatch repair proteins revealed a marked decrease of expression of PMS2 in U2-OS/Pt cells, which also exhibited microsatellite instability. Studies on DNA mismatch repair deficient and proficient colon carcinoma cells were consistent with a lack of influence of the DNA mismatch repair status on BBR 3464 cytotoxicity. In conclusion, the cytotoxic potency and the ability of the triplatinum complex to overcome cisplatin resistance appear to be related to a different mechanism of DNA interaction (formation of different types of drug-induced DNA lesions) as compared to conventional mononuclear complexes.

Adaptor Proteins, Signal Transducing↗
PubMed2004

Molecular analysis of endometrial hyperplasia in HNPCC-suspicious patients may predict progression to endometrial carcinoma.

Women predisposed to hereditary nonpolyposis colorectal cancer are at high risk of developing endometrial carcinoma at a young age. Hereditary nonpolyposis colorectal cancer-associated endometrial carcinomas are of the endometrioid type, usually arise from complex atypical hyperplasia, and often show microsatellite instability. To identify occult hereditary nonpolyposis colorectal cancer individuals among endometrial carcinoma patients, we examined complex atypical hyperplasias and endometrial carcinomas of 60 women < or =50 years of age (mean age: 35.7 years) using microsatellite instability, immunohistochemistry, and DNA sequence analysis. Three patient groups were recruited: group 1, patients with complex atypical hyperplasia exclusively (n = 27); group 2, patients with complex atypical hyperplasia and synchronous or metachronous endometrial carcinoma (n = 15); group 3, patients with endometrial carcinoma only (n = 18). Overall, 13 of 33 endometrial carcinomas (39%) displayed high-level microsatellite instability. None of the complex atypical hyperplasias in group 1 had high-level microsatellite instability or loss of hMLH1/hMSH2 protein expression. In group 2 patients, 33% of complex atypical hyperplasias and 53% of endometrial carcinomas had high-level microsatellite instability. Loss of hMSH2 protein expression was found in six endometrial carcinoma patients, five of them with verified hMSH2 germline mutations, including four patients with high-level microsatellite instability in complex atypical hyperplasia. Among group 3 patients, 28% of endometrial carcinomas displayed high-level microsatellite instability; three of those five endometrial carcinomas were from patients with multiple extrauterine hereditary nonpolyposis colorectal cancer-associated tumors. We conclude that young women (< or =50 years of age) with concurrent complex atypical hyperplasia and multiple hereditary nonpolyposis colorectal cancer-associated carcinomas are at risk of developing high-level microsatellite instability endometrial carcinoma. Combined microsatellite instability and immunohistochemistry analysis allows the identification of a high proportion of hereditary nonpolyposis colorectal cancer patients among young women with endometrial carcinoma and complex atypical hyperplasia. All complex atypical hyperplasias with high-level microsatellite instability progressed to endometrial carcinoma. Only one third of the complex atypical hyperplasias with microsatellite stability progressed to high-level microsatellite instability endometrial carcinoma, while seven complex atypical hyperplasias progressed to microsatellite stability endometrial carcinoma. Microsatellite analysis of complex atypical hyperplasia in young patients may therefore be a useful prognostic marker for predicting possible progression to high-level microsatellite instability endometrial carcinomas.

Adenocarcinoma↗
PubMed2003

Alteration of the fragile histidine triad gene in intrahepatic cholangiocarcinoma.

BACKGROUND AND AIMS: Intrahepatic cholangiocarcinoma is the second most common intrahepatic neoplasm, accounting for 10-30% of primary liver cancers. Since little is known about the development of this cancer, we searched for alterations to the fragile histidine triad (FHIT) gene, a putative tumour suppressor gene on chromosome 3p14.2. In addition, we investigated oncogenic mutations in beta-catenin, which lead to an activated Wnt signalling pathway and microsatellite instability as a consequence of mismatch repair deficiency. METHODS AND RESULTS: Loss of heterozygosity at the FHIT/FRA3B locus was detected in two out of ten informative cases (20%) using the marker D3S1300 and in one out of seven informative cases (14%) by marker D3S1234. Furthermore, immunohistochemistry revealed loss of Fhit expression in most of the 19 intrahepatic cholangiocarcinomas analysed, although to varying degrees. Oncogenic mutations were excluded in exon 3 of the beta-catenin gene by restriction enzyme digest and DNA sequence analysis. Microsatellite instability could not be detected in the tumour specimens tested using a validated marker panel. In two out of nine informative cases (22%), loss of heterozygosity was displayed close to the adenomatous polyposis coli (APC) gene. CONCLUSIONS: Alterations to FHIT/FRA3B were initially detected by allelic losses of genomic DNA in intervening sequences of this tumour suppressor gene. Immunohistochemistry extended this initial observation by demonstrating that seven of the 19 intrahepatic cholangiocarcinomas had entirely lost expression of FHIT. Loss of Fhit protein in only a subpopulation of tumour cells due to oligoclonality may explain the varying portions of negative staining observed in the other tumour samples. Microsatellite instability did not appear to contribute to the development of intrahepatic cholangiocarcinoma in the cohort of tumours we analysed. Furthermore, the Wnt pathway may be constitutively turned on by inactivation of the APC gene due to deletion of genomic DNA but not by oncogenic mutations within exon 3 of the beta-catenin gene.

Acid Anhydride Hydrolases↗
PubMed2001

Resistance to topoisomerase poisons due to loss of DNA mismatch repair.

Sporadic breast carcinomas demonstrate microsatellite instability, reflecting the presence of DNA mismatch repair-deficient cells, in about one fourth of cases at the time of diagnosis. Loss of DNA mismatch repair has been reported to result in resistance not only to cisplatin and alkylating agents but also to the topoisomerase II poison doxorubicin, suggesting an association between DNA mismatch repair and topoisomerase II poison-induced cytotoxicity. Our study investigates the relationship between loss of MSH2 or MLH1 function and sensitivity to the topoisomerase I and II poisons, and to the taxanes, 2 classes of cytotoxic drugs commonly used in breast cancer. Two pairs of cell lines proficient and deficient in mismatch repair due to loss of either MSH2 or MLH1 function were used. Loss of either MSH2 or MLH1 function resulted in resistance to the topoisomerase II poisons doxorubicin, epirubicin and mitoxantrone, whereas only loss of MLH1 function was associated with low-level resistance to the topoisomerase I poisons camptothecin and topotecan. In contrast, there was no resistance to docetaxel and paclitaxel. Our data support the hypothesis that both MSH2 and MLH1 are involved in topoisomerase II poison-mediated cytotoxicity, whereas only MLH1 is involved in topoisomerase I poison-mediated cytotoxicity. Since our study shows that loss of DNA mismatch repair does not result in resistance to the taxanes, these drugs can be recommended for use in breast cancer deficient in mismatch repair.

Adaptor Proteins, Signal Transducing↗
PubMed2001

Microsatellite instability, expression of hMSH2 and hMLH1 and HPV infection in cervical cancer and their clinico-pathological association.

Infection with specific genotypes of human papillomavirus (HPV) has been strongly implicated in cervical carcinogenesis. However, HPV infection alone is insufficient for malignant transformation of the cervical epithelium. An alteration of microsatellite repeats is the result of slippage owing to strand misalignment during DNA replication and is referred to as microsatellite instability (MSI). These defects in DNA repair pathways have been related to human carcinogenesis; however, the role of MSI in the tumorigenesis of cervical cancer remains unclear. The clinical and pathological features of cervical cancers which are MSI-positive have also not been fully characterized. This study investigated the prevalence of MSI in cervical cancer and its relationship to clinico-pathological characteristics and HPV infection. Polymerase chain reaction-based microsatellite assay combined with tissue microdissection was used to examine for MSI in 50 cervical squamous cell carcinomas in Hong Kong women. In addition, the immunohistochemical staining was performed to determine the expression of major DNA mismatch repair genes, hMSH2 and hMLH1. Six cases (12%) displayed a low frequency of MSI (MSL-L) showing MSI at one locus only in 5 loci examined. Seven cases (14%) showed a high frequency of MSI (MSI-H) having MSI at 2 or more loci. Grouping MSI-L and MSI-H cases together as MSI-positive, statistical analysis of HPV infection, tumor grade, clinical stage and clinical status failed to disclose differences between MSI-positive and MSI-negative cases (p > 0.05). However, MSI-H correlated with advanced stage of disease (p < 0.05). Individuals with MSI-H tumors appeared to have reduced overall survival compared to individuals with MSI-L and MSI-negative tumors, but the difference was not statistically significant (p = 0.059). An absence of either MSH2 or MLH1 expression was observed in 2 MSI-L and 4 MSI-H cases, respectively. The results suggest that MSI is present in a subgroup of cervical squamous cell carcinomas, and defects resulting in MSI may be related to tumor progression and possibly poor prognosis in cervical cancer.

Adaptor Proteins, Signal Transducing↗
PubMed1995

Occurrence of microsatellite instability in gastric carcinoma is associated with enhanced expression of erbB-2 oncoprotein.

To investigate the molecular mechanism of gastric carcinogenesis, we examined simultaneously the frequency of microsatellite instability and the immunoreactivities to ras, erbB-2, and p53 in 42 gastric adenocarcinoma tissues. Microsatellite instability, measured by DNA replication error, was detected in 33.3% (14/42) of patients with gastric carcinoma while positive immunostaining was demonstrated in 3.1% (1/32) for ras, 40.5% (17/42) for erbB-2, and 28.6% (12/42) for p53. There was no statistical difference between the intestinal type and the diffuse type of carcinoma with respect to microsatellite instability, ras, or erbB-2 expression. The expression of p53 occurred more frequently in the intestinal type of carcinoma (41.7%, 10/24) than in the diffuse type of carcinoma (11.1%, 2/18; P < 0.01). There was no association between microsatellite instability and ras or p53 expression, while enhanced expression of erbB-2 occurred more frequently in carcinomas with microsatellite instability (64.3%, 9/14) than in those without microsatellite instability (28.6%, 8/28; P < 0.05). Such a strong association between microsatellite instability and erbB-2 oncogene may be responsible for the increase of other oncogenic mutations and tumor progression in gastric carcinogenesis.

DNA, Neoplasm↗
PubMed1997

Microsatellite instability in yeast: dependence on repeat unit size and DNA mismatch repair genes.

We examined the stability of microsatellites of different repeat unit lengths in Saccharomyces cerevisiae strains deficient in DNA mismatch repair. The msh2 and msh3 mutations destabilized microsatellites with repeat units of 1, 2, 4, 5, and 8 bp; a poly(G) tract of 18 bp was destabilized several thousand-fold by the msh2 mutation and about 100-fold by msh3. The msh6 mutations destabilized microsatellites with repeat units of 1 and 2 bp but had no effect on microsatellites with larger repeats. These results argue that coding sequences containing repetitive DNA tracts will be preferred target sites for mutations in human tumors with mismatch repair defects. We find that the DNA mismatch repair genes destabilize microsatellites with repeat units from 1 to 13 bp but have no effect on the stability of minisatellites with repeat units of 16 or 20 bp. Our data also suggest that displaced loops on the nascent strand, resulting from DNA polymerase slippage, are repaired differently than loops on the template strand.

Chromosome Mapping↗
PubMed1999

Mitochondrial gene mutation, but not large-scale deletion, is a feature of colorectal carcinomas with mitochondrial microsatellite instability.

We have shown that microsatellite instability (MSI) occurs in mitochondrial DNA (mtDNA) of colorectal carcinomas. To determine whether such mitochondrial microsatellite instability (mtMSI) is associated with certain forms of mitochondrial gene alterations, we extended the screening in the same series of 45 carcinomas. Analysis by whole mtDNA amplification (16.5 kb) and digestion revealed no detectable large-scale change in these carcinomas. In contrast, single-strand conformation polymorphism (SSCP) analysis demonstrated NADH dehydrogense (ND) gene alterations in 7 carcinomas (16%), including 3 mononucleotide repeat alterations, 2 missense mutations and 1 small (15 bp) deletion. Six of these 7 carcinomas also exhibited mtMSI of the (C)n sequence in the displacement-loop (D-loop) region. Thus, frameshift or missense mutations rather than large-scale changes in the mtDNA were more common features in colorectal carcinomas with mtMSI. By analogy to mutational features of nuclear MSI, mtMSI most likely results from certain repair deficiencies in the mtDNA and probably plays a role in the tumor development of certain colorectal carcinomas.

Carcinoma↗
PubMed2005

Genetic and epigenetic changes of components affecting the WNT pathway in colorectal carcinomas stratified by microsatellite instability.

An unselected series of 310 colorectal carcinomas, stratified according to microsatellite instability (MSI) and DNA ploidy, was examined for mutations and/or promoter hypermethylation of five components of the WNT signaling cascade [APC, CTNNB1 (encoding beta-catenin), AXIN2, TCF4, and WISP3] and three genes indirectly affecting this pathway [CDH1 (encoding E-cadherin), PTEN, and TP53]. APC and TP53 mutations were each present more often in microsatellite-stable (MSS) tumors than in those with MSI (P < .001 for both). We confirmed that the aneuploid MSS tumors frequently contained TP53 mutations (P < .001), whereas tumors with APC mutations and/or promoter hypermethylation revealed no associations to ploidy. Mutations in APC upstream of codons 1020 to 1169, encoding the beta-catenin binding site, were found in 15/144 mutated tumors and these patients seemed to have poor clinical outcome (P = .096). Frameshift mutations in AXIN2, PTEN, TCF4, and WISP3 were found in 20%, 17%, 46%, and 28% of the MSI tumors, respectively. More than half of the tumors with heterozygote mutations in AXIN2 were concurrently mutated in APC. The present study showed that more than 90% of all samples had alteration in one or more of the genes investigated, adding further evidence to the vital importance of activated WNT signaling in colorectal carcinogenesis.

Adenomatous Polyposis Coli Protein↗
PubMed1996

Mutations of the transforming growth factor-beta type II receptor gene are strongly related to sporadic proximal colon carcinomas with microsatellite instability.

BACKGROUND: Mutations of the transforming growth factor-beta type II receptor gene (TGF-beta RII) have been found in several replication error-positive sporadic colorectal carcinomas and hereditary nonpolyposis colorectal carcinoma cell lines. The aim of this study was to clarify the role of TGF-beta RII in sporadic colorectal carcinogenesis. METHODS: The authors screened for mutations at simple repeated sequences in the TGF-beta RII gene by polymerase chain reaction-single strand conformation polymorphism. They also examined genomic instability, using five microsatellite DNA markers in 69 sporadic colorectal carcinomas. When the carcinomas exhibited the TGF-beta RII mutations, the authors screened further for mutations in two DNA mismatch repair genes, hMSH2 and hMLH1. RESULTS: Seven of the 69 cancers (10%) showed one or two A deletions in TGF-beta RII and resultant frameshift mutations in nucleotide positions 709-718 containing a (A) 10 repeated sequence; but none of these appeared in the corresponding normal DNA, indicating a somatic mutation. All of the seven cancers were located in the proximal colon; there were none in the distal colon (P < 0.01). On the other hand, 22 of the 69 carcinomas (32%) showed the replication error-positive phenotype. The frequency of replication errors in proximal colon carcinomas was higher than that in distal colon carcinomas (P < 0.05). All 7 cancers with TGF-beta RII mutations showed replication errors. One of them revealed a nonsense mutation at codon 413, and 1 revealed a loss of heterozygosity in hMSH2. CONCLUSIONS: These data indicate that mutations of TGF-beta RII are strongly related to proximal colon carcinomas with microsatellite instability and that the mechanism of carcinogenesis in some proximal colon carcinomas is similar to that in hereditary nonpolyposis colorectal carcinoma.

Aged↗
PubMed2004

The role of hMSH3 and hMSH6 in ovarian endometrioid carcinoma and relationship with microsatellite instability phenotype.

Frequent frameshift mutations in the DNA mismatch repair genes hMSH3, and hMSH6, have been reported in colorectal and endometrial cancers with microsatellite instability, however, it is unclear whether they are similarly altered in ovarian endometrioid carcinoma. In this study, we examined frequency of frameshift mutation and protein expression in hMSH3 and hMSH6 in ovarian endometrioid carcinoma with or without microsatellite instability. Only 1 frameshift mutation of the 16 cases with microsatellite instability-high phenotype (6%) was detected in poly(A)8 tract of the hMSH3, but not in poly(C)8 tract of hMSH6 genes. In addition, none of the 6 microsatellite instability-low or 20 microsatellite-stable tumors showed mutations in these regions in either gene. These results indicate that mutations in the mono-nucleotide tracts of hMSH3 and hMSH6 are infrequent in ovarian endometrioid adenocarcinomas, other mechanisms may play a more important role in the development of these tumors.

Base Sequence↗
PubMed1998

Assessment of microsatellite instability in a cell line from a patient with xeroderma pigmentosum variant.

Cells from patients with xeroderma pigmentosum (XP) variant are thought to be defective in postreplication repair. This DNA repair pathway is not well defined in human cells and the exact genetic defect of XP variant is unknown. In another cancer-prone hereditary disorder, hereditary nonpolyposis colon cancer, tumors are characterized by a DNA mismatch repair defect with microsatellite instability. Since there are some similarities between postreplication repair and mismatch repair, we investigated microsatellite instability, the hallmark of a DNA mismatch repair defect, in a lymphoblastoid cell line from a patient with XP variant. Two normal lines and one nucleotide excision repair-defective XP group A line were used as controls. In a host cell microsatellite instability assay, the recently developed shuttle vector pZCA29 was transfected into these cells and replicated plasmid recovered after 3 days. The plasmid contains two CA repeat tracts that interrupt the reading frame of the lacZ gene. Reversion to active beta-galactosidase, detectable by a color reaction of bacterial transformants, represents the frequency of frameshift mutations in the CA repeat tracts during replication of the plasmid, and thereby the host cells' microsatellite instability. We did not find any significant differences in the mutation frequencies of the plasmids after passage through either cell line. This indicates that there is no microsatellite instability in the examined XP variant cell line.

Cell Line↗
PubMed1999

MLH1 promoter methylation and gene silencing is the primary cause of microsatellite instability in sporadic endometrial cancers.

Defective DNA mismatch repair in human tumors leads to genome-wide instability of microsatellite repeats and a molecular phenotype referred to as microsatellite instability (MSI). MSI has been reported in a variety of cancers and is a consistent feature of tumors from patients with hereditary non-polyposis colorectal cancer. Approximately 20% of cancers of the uterine endometrium, the fifth most common cancer of women world-wide, exhibit MSI. Although the frequency of MSI is higher in endometrial cancers than in any other common malignancy, the genetic basis of MSI in these tumors has remained elusive. We investigated the role that methylation of the MLH1 DNA mismatch repair gene plays in the genesis of MSI in a large series of sporadic endometrial cancers. The MLH1 promoter was methylated in 41 of 53 (77%) MSI-positive cancers investigated. In MSI-negative tumors on the other hand, there was evidence for limited methylation in only one of 11 tumors studied. Immunohistochemical investigation of a subset of the tumors revealed that methylation of the MLH1 promoter in MSI-positive tumors was associated with loss of MLH1 expression. Immunohistochemistry proved that two MSI-positive tumors lacking MLH1 methylation failed to express the MSH2 mismatch repair gene. Both of these cancers came from women who had family and medical histories suggestive of inherited cancer susceptibility. These observations suggest that epigenetic changes in the MLH1 locus account for MSI in most cases of sporadic endometrial cancers and provide additional evidence that the MSH2 gene may contribute substantially to inherited forms of endometrial cancer.

Adaptor Proteins, Signal Transducing↗
PubMedDate not supplied

Loci for efficient detection of microsatellite instability in hereditary non-polyposis colorectal cancer.

Most hereditary non-polyposis colorectal cancer (HNPCC) is due to germline mutations in DNA mismatch repair genes. Tumors arising as a result of these mutations display instability in microsatellites, which are short tandem repeats of DNA that are distributed throughout the genome. Although a subset of sporadic colorectal carcinomas also have microsatellite instability (MSI), the phenotype is a useful screening test in identifying patients with HNPCC caused by mutations in mismatch repair (MMR) genes. Studies have shown that some microsatellite markers are more efficient than others in identifying tumors with MSI. Furthermore, the frequency of instability can be assessed by categorizing patients into high (MSI-H, >/= 30-40% positive markers), low (MSI-L), and microsatellite stable (MSS) groups. Using a panel of 28 microsatellite markers, tumor and normal DNA from 10 HNPCC patients was used to identify the five most efficient markers for detecting MSI (BAT26, D2S123, FGA, D18S35, and TP53-DI). Each of the five markers detected MSI in 80-100% of the cases examined. We then expanded the sample size to 17 tumors from HNPCC patients. Each case had evidence for a mutation in either hMSH2 or hMLH1. We compared the efficiency of our panel of five best markers with another panel of five markers (BAT25, BAT26, D2S123, D17S250, and D5S346) identified as being efficient markers for detection of MSI at a recent NCI workshop. Our five selected markers were more efficient (85% vs. 79%) in detecting MSI. However, using either panel, 100% of the cases fell into the MSI-H category and the probability of misclassifying an MSI-H case as MSI-L is very low (0.002-0.008). We also examined four cases meeting the Amsterdam criteria for HNPCC, but with no evidence for mutation in either the hMSH2 or hMLH1 gene. With our panel, three were classified as MSI-H, while only two were classified as such with the NCI reference panel. The probability of misclassifying an MSI-L case as an MSI-H, using a panel of five markers is high (0.263).

Basic Helix-Loop-Helix Proteins↗