Microsatellite instability is a predictive factor of the tumor response to irinotecan in patients with advanced colorectal cancer

The aim of our study was to assess the relationship between colorectal tumor responsiveness to irinotecan and microsatellite instability (MSI), a feature of colorectal tumors with DNA mismatch repair defect. Seventy-two patients with metastatic colorectal cancer were included in our retrospective study. A complete response to irinotecan was observed in 1 patient and a partial response in 10 patients, whereas 61 patients did not respond to this treatment. We analyzed the protein expression of hMLH1, hMSH2, and BAX by immunohistochemistry, determined the MSI phenotype, and looked for mutations in the coding repeats located in the transforming growth factor beta-RII, BAX, hMSH3, and hMSH6 genes. All 44 tumors analyzed expressed detectable levels of hMLH1; 1 tumor lacked hMSH2 staining, whereas 4 tumors showed a marked decrease in BAX expression. A better response to irinotecan was observed in the patients whose tumors have lost BAX expression (P < 0.001). Among the 7 tumors that displayed a MSI-H phenotype, 4 responded to irinotecan, whereas only 7 of the 65 MSI-L/ microsatellite stable tumors did (P = 0.009). Seven of the 72 tumors had inactivating mutations in the coding repeats of the target genes. Three tumors displayed a mutation in the poly-A10 tract of the transforming growth factor beta-RII gene, associated with a 1-bp deletion in the poly-A8 tract of hMSH3 in one tumor and with a 1-bp deletion in the poly-G8 tract of BAX in another. Four tumors displayed mutations in the poly-G8 repeat of BAX, whereas 2 mutations in hMSH6 and hMSH3 were characterized. Among the 7 tumors with mutations in these target genes, 5 responded to irinotecan, whereas only 6 of the other 65 tumors did (P < 0.001), indicating that MSI-driven inactivation of target genes modifies tumor chemosensitivity. Our observations allowed us to define the first useful predictive criteria for irinotecan response in patients with colorectal cancer.     

Frameshift mutations and a length polymorphism in the hMSH3 gene and the spectrum of microsatellite instability in sporadic colon cancer.

Mutations in the hMVSH3 gene in sporadic colon cancer with microsatellite instability (MSI) were investigated, since several mismatch repair genes were known to be mutated in cancers with MSI, but only deletions in the (A)8 region in the hMSH3 gene have been reported. We also analyzed the relationships between hMSH3 mutations and the spectrum of MSI. We screened MSI in 79 sporadic colon cancer samples using mono- and dinucleotide repeat markers and the samples with MSI were further analyzed for tri- and tetranucleotide repeat instability and mutations in the hMSH3 gene by polymerase chain reaction-single strand conformation polymorphism (PCR-SSCP) analysis. Five (6%) out of 79 tumors were MSI-H and 15 (19%) were MSI-L. Two MSI-H tumors showed insertion in the (C)8 region in the hMSH6 gene and one tumor showed insertion and deletion in the (A)8 region in the hMSH3 gene, and two of the three above tumors showed MSI in tri-and tetranucleotide repeats. One MSI-L tumor showed somatic alteration in a 9-bp repeat sequence in hMSH3. No frameshift mutations were found in the (A)7 and (A)6 regions in hMSH3. Thus, we confirmed that the (A)8 region in hMSH3 is a hot spot and mutations in the (A)7 and (A)6 regions in hMSH3 are not common. The hMSH3 mutation may enhance genomic instability in some colorectal cancers.     

Genetic alterations of sporadic colorectal cancer with microsatellite instability, especially characteristics of primary multiple colorectal cancers

BACKGROUND AND OBJECTIVES: The purpose of this study was to elucidate genetic alterations of sporadic colorectal cancers with Microsatellite instability (MSI). METHODS: One hundred and ten patients with sporadic colorectal cancer were examined. The MSI was assessed using eight microsatellite markers. In addition, mutation analysis was performed for Transforming growth-beta type II receptor (TGF beta R II), bcl-2 associated X protein (BAX), Insulin-like growth factor II receptor (IGF II R), human MutS homolog 3 (hMSH3), human MutS homolog 6 (hMSH6), human MutS homolog 2 (hMSH2), and human MutL homolog 1 (hMLH1) genes. Tumors with three or more positive loci have been determined to be MSI-H (high-frequency MSI), tumors with one or two positive loci were designated as MSI-L (low-frequency MSI) and tumors lacking apparent instability were designated as MSS (microsatellite stable). RESULTS: There were 11 cases with MSI-H (MSI-H group) and 99 cases with MSI-L/MSS (MSI-L/MSS group). The frequency of cases with multiple colorectal cancer in the MSI-H group was significantly higher than that of MSI-L and MSS group (81.8% vs. 34.3%, p = 0.0022). The frequency of cases with multiple cancers increased as the number of locus with microsatellite instability increased. Among 11 tumors with MSI-H, 7 indicated mutation of the TGF beta R II (63.6%), whereas no tumor had a mutation of the TGF beta R II among 20 tumors with MSI-L (p = 0.0001). Regarding the BAX, hMSH3, hMSH6 gene, the same trend was obtained as the TGF beta R II gene (18.2% vs. 0%, p = 0.0487, 36.4% vs. 0%, p = 0.0039, 27.3% vs. 0%, p = 0.0140, respectively). Only two cases indicated a somatic point mutation of the hMSH2 gene. CONCLUSIONS: The multiple occurrence of the colorectal carcinoma may be related to MSI-H as well as the mutation of genes possessing repetitive mononucleotide tracts. Furthermore, we recommend strict follow-up in sporadic colorectal patients that indicate MSI-H.     

Differential expression of hMLH1 and hMSH2 is related to bladder cancer grade,stage and prognosis but not microsatellite instability

Defects in the DNA mismatch repair proteins result in microsatellite instability and malignancy in hereditary non-polyposis colorectal carcinoma (HNPCC). However, the role of mismatch repair (MMR) proteins and microsatellite instability (MSI) in transitional cell carcinoma of the bladder is less clear. In our study, the expression of 2 MMR proteins and the frequency of MSI in Transitional cell carcinoma of the bladder (TCC) were investigated. One hundred eleven patients with TCC of the bladder were studied, with complete clinicopathological data (median follow up of 5 years, range 5-16 years). Immunohistochemistry was used to detect the expression levels of hMLH1 and hMSH2. Microsatellite analysis for 14 loci (10 loci from the Bethesda consensus panel and the repeats in the TGFbetaR2, BAX, hMSH3 and hMSH6 genes) was performed on 84 tumors. Reduced expression of either MMR protein was seen in 26 of 111 tumors (23%). Reduced expression was seen more commonly in muscle invasive (p<0.03) and high grade TCC (p<0.03) than in superficial, low grade tumors. By 5 years, reduced expression of either MMR protein was associated with fewer recurrences of superficial tumors (p=0.015) and fewer relapses in all tumors (p=0.03), compared to tumors with normal expression. Nine tumors had reduced expression of both MMR proteins, analysis which suggests a synergistic reduction in expression (p=0.001). MMR expression was related to patient age, younger patients being more likely to have reduced MMR expression than older patients (p<0.01). MSI was seen at multiple loci in 1 tumor (1%) and at a single locus in 6 tumors (7%). MSI was not associated with MMR expression. Our findings indicate that reduced expression of the MMR proteins may have an important contribution in the development of a subset of TCCs and suggest a potential role for MMR expression as prognostic indicators.     

Microsatellite instability testing in colorectal carcinoma: choice of markers affects sensitivity of detection of mismatch repair-deficient tumors.

PURPOSE: Microsatellite instability (MSI) is found in 10% to 15% of sporadic colorectal tumors and is usually caused by defects in DNA mismatch repair (MMR). In 1997, a panel of microsatellite markers including mononucleotide and dinucleotide repeats was recommended by a National Cancer Institute workshop on MSI. We investigated the relationship between instability of these markers and MMR protein expression in a cohort of sporadic colorectal cancer patients. EXPERIMENTAL DESIGN: Paraffin sections of normal and tumor tissue from 262 colorectal cancer patients were examined for MSI status by PCR amplification and for MMR protein expression using antibodies against hMLH1, hPMS2, hMSH2, and hMSH6. RESULTS: Twenty-six (10%) of the patients studied had tumors with a high level of MSI (MSI-H). The frequencies of MSI were the same in African-American and Caucasian patients. Each of the MSI-H tumors had mutations in both mononucleotide and dinucleotide repeats and had loss of MMR protein expression, as did two tumors that had low levels of MSI (MSI-L). These two MSI-L tumors exhibited mutations in mononucleotide repeats only, whereas eight of the other nine MSI-L tumors had mutations in just a single dinucleotide repeat. There was not a statistically significant difference in outcomes between patients whose tumors were MMR-positive or MMR-negative, although there was a slight trend toward improved survival among those with MMR-deficient tumors. CONCLUSIONS: The choice of microsatellite markers is important for MSI testing. Examination of mononucleotide repeats is sufficient for detection of tumors with MMR defects, whereas instability only in dinucleotides is characteristic of MSI-L/MMR-positive tumors.     

Genes involved in DNA repair are mutational targets in endometrial cancers with microsatellite instability

Microsatellite instability (MSI) is observed in a subset of endometrial cancers (ECs) and is attributed to defects in mismatch repair. Mismatch repair deficiency allows for accumulation of mutations in the coding repeats of key target genes, which may be involved in the initiation and progression of MSI+ EC. We examined genes implicated in DNA repair pathways in 38 MSI-high (MSI-H), 10 MSI-low, 25 microsatellite stable ECs, and a selected panel of associated premalignant hyperplasias. Genetic alterations were correlated to histopathological data, including tumor grade and stage. Somatic frameshift mutations were observed in hMLH3, hMSH3, hMSH6, CHK1, and BAX genes in MSI-H endometrial hyperplasias and cancers, whereas mutations in ATR and CDC25C were observed only in MSI-H ECs. Increased mutation frequency in DNA damage response pathway genes including ATR, CHK1, and BAX demonstrated a significant trend with advancing tumor grade (P < 0.05). Our observations of the same mutations at short coding mononucleotide repeats in both premalignant lesions and tumors and association of increased frequency of mutation accumulation with advancing tumor grade suggest that these alterations may play a role in the development and progression of MSI+ EC.     

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.     

Loss of heterozygosity,microsatellite instability,and mismatch repair protein alterations in the radial growth phase of cutaneous malignant melanomas

Little is known about genomic alterations during development of the radial growth phase (RGP) of cutaneous malignant melanomas (CMMs). In this investigation polymerase chain reaction-based microsatellite assays were applied to analyze 13 RGP-CMMs with 18 microsatellite markers at six chromosomal regions: 1p, 3p, 4q, 6q, 9p, and 10q. Loss of heterozygosity (LOH) was found in eight cases (62%), at 9p22, 1p36, and 10q11, suggesting the presence of tumor-suppressor genes at these regions. LOH was encountered frequently at the interferon-alpha (31%) and D10S249 loci (15%). Low-level microsatellite instability (MSI) (11-16% of investigated loci unstable) was noted in three cases (23%). Two MSI banding patterns were seen: band shift and the presence of additional bands. To investigate the underlying mechanisms of the low-level MSI pattern, we analyzed the lesions for expression of mismatch repair (MMR) proteins with immunoperoxidase methods and mouse monoclonal antibodies. The average percentages of positively stained cells for human MutL homolog 1 (hMLH1), human MutS homolog 2 (hMSH2), and human MutS homolog 6 (hMSH6) in RGP-CMM (75.6 +/- 3.4%, 67.20 +/- 7.71%, and 76.6 +/- 2.1%, respectively) were reduced compared with benign nevi. No statistically significant differences in MMR protein expression were found between microsatellite-stable and low-level MSI lesions (P = 0.173, P = 0.458, and P = 0.385 for hMLH1, hMSH2, and hMSH6, respectively). There was a direct correlation between values for percentages of positively stained cells for hMSH2 and hMSH6 (r = +0.9, P = 0.03), suggesting that common mechanisms regulate their expression. In conclusion, LOH, MSI, and reduced MMR protein expression appear to be present in at least some RGP-CMMs and may play a role in their pathogenesis. Further studies are necessary to support these finding and to determine their diagnostic and prognostic significance.     

Frameshift Mutations and a Length Polymorphism in the hMSH3 Gene and the Spectrum of Microsatellite Instability in Sporadic Colon Cancer

Mutations in the hMSH3 gene in sporadic colon cancer with microsatellite instability (MSI) were investigated, since several mismatch repair genes were known to be mutated in cancers with MSI, but only deletions in the (A)₈ region in the hMSH3 gene have been reported. We also analyzed the relationships between hMSH3 mutations and the spectrum of MSI. We screened MSI in 79 sporadic colon cancer samples using mono- and dinucleotide repeat markers and the samples with MSI were further analyzed for tri- and tetranucleotide repeat instability and mutations in the hMSH3 gene by polymerase chain reaction-single strand conformation polymorphism (PCR-SSCP) analysis. Five (6%) out of 79 tumors were MSI-H and 15 (19%) were MSI-L. Two MSI-H tumors showed insertion in the (C)₈ region in the hMSH6 gene and one tumor showed insertion and deletion in the (A)₈ region in the hMSH3 gene, and two of the three above tumors showed MSI in tri-and tetranucleotide repeats. One MSI-L tumor showed somatic alteration in a 9-bp repeat sequence in hMSH3. No frameshift mutations were found in the (A)₇ and (A)₆ regions in hMSH3. Thus, we confirmed that the (A)₈ region in hMSH3 is a hot spot and mutations in the (A)₇ and (A)₆ regions in hMSH3 are not common. The hMSH3 mutation may enhance genomic instability in some colorectal cancers.     

Characterization of sporadic colon cancer by patterns of genomic instability

Colorectal cancer (CRC) can progress through two pathways of genomic instability: chromosomal (CIN) and microsatellite instability (MSI). We hypothesized that these two pathways are not always independent and that some tumors therefore show a significant degree of overlap between these two mechanisms. We classified 209 high-risk stage II and stage III sporadic CRCs based on their MSI status, using a National Cancer Institute-recommended panel of microsatellite markers, and also identified MSI-associated mutations of CRC target genes such as TGFbetaRII. Evidence for CIN was gathered by identifying loss of heterozygosity (LOH) events on chromosomal arms 1p, 2p, 3p, 5q, 17p, and 18q, which are regions harboring mismatch-repair and tumor-suppressor genes that are significant in CRC development. Results of all molecular markers tested were correlated with clinicopathological variables of the cohort, including treatment outcome. Of the 209 cases, 65% cancers were microsatellite stable, 21% were MSI-low, and 14% were MSI-high (MSI-H). Overall, 51% of the tumors had at least one LOH event, with most frequent chromosomal losses observed on 18q (72.5%), followed by 5q (22%), 17p (21%), and 3p (14%). Interestingly, we observed a significant degree of overlap between MSI and CIN pathways. Of 107 cancers with LOH events, 7 (6.5%) were also MSI-H, and of 30 cancers that were MSI-H, 7 (23.3%) also had one or more LOH events. We also found that 37.8% of microsatellite-stable cancers had no LOH events identified, thus comprising a subgroup of tumors that were not representative of either of these two pathways of genomic instability. Our data suggest that molecular mechanisms of genomic instability are not necessarily independent and may not be fully defined by either the MSI or CIN pathways.     

Microsatellite instability and mutation analysis of candidate genes in unselected sardinian patients with endometrial carcinoma

BACKGROUND: Microsatellite instability (MSI) is due mostly to a defective DNA mismatch repair (MMR). Inactivation of the two principal MMR genes, hMLH1 and hMSH2, and the PTEN tumor suppressor gene seems to be involved in endometrial tumorigenesis. In this study, Sardinian patients with endometrial carcinoma (EC) were analyzed to assess the prevalence of both the mutator phenotype (as defined by the presence of MSI and abnormal MMR gene expression at the somatic level) and the hMLH1, hMSH2, and PTEN germline mutations among patients with MSI positive EC. METHODS: Paraffin embedded tissue samples from 116 consecutive patients with EC were screened for MSI by polymerase chain reaction-based microsatellite analysis. Immunohistochemistry (IHC) with anti-hMLH1 and anti-hMSH2 antibodies was performed on MSI positive tumor tissue sections. Germline DNA was used for mutational screening by denaturing high-performance liquid chromatography analysis and automated sequencing. RESULTS: Thirty-nine patients with EC (34%) exhibited MSI; among them, 25 tumor samples (64%) showed negative immunostaining for hMLH1/hMSH2 proteins (referred to as IHC negative). No disease-causing mutation within the coding sequences of the hMLH1/hMSH2 and PTEN genes was found in patients with EC who had the mutator phenotype (MSI positive and IHC negative), except for a newly described hMLH1 missense mutation, Ile655Val, that was observed in 1 of 27 patients (4%). Although MSI was more common among patients with advanced-stage EC and increased as the tumor grade increased, no significant correlation with disease free survival or overall survival was observed among the two groups (MSI positive or MSI negative) of patients with EC. CONCLUSIONS: In patients with MSI positive EC, epigenetic inactivations rather than genetic mutations of the MMR genes seem to be involved in endometrial tumorigenesis. No prognostic value was demonstrated for MSI in patients with EC.     

Microsatellite instability mutator phenotype in hepatocellular carcinoma in non-alcoholic and non-virally infected normal livers

Microsatellite instability (MSI) seems to be a rare event in hepatocarcinogenesis and might actually be associated with the progression of hepatocellular carcinoma (HCC) in which the liver is often the site of chronic hepatitis or cirrhosis. The aim of this work was to define the MSI phenotype in HCC affecting exclusively normal livers to avoid slippage errors due to cirrhosis. One hundred and sixty-four patients with HCC affecting non-cirrhotic livers were operated on in our hospital between 1984 and 2001. We analyzed 37 patients selected for low alcohol consumption and the absence of HBV or HCV infection. All the livers were histologically normal. MSI was analyzed according to the criteria defined during the conference consensus workshop for colorectal cancer. High MSI (MSI-H > 30%) was found in 6 (16%) and low MSI (MSI-L < 30%) in 10 (27%) of the 37 HCCs. None of the 10 microsatellite markers tested were altered in the remaining 21 tumors (57%). Immunohistochemistry showed that normal amounts of hMLH1 and hMSH2 were present both in MSI-H and in MSI-L HCCs. MSI-H was significantly associated with more aggressive histological tumor features and a shorter median delay before recurrence. Thus, we have found a small subgroup of HCC tumors which can be considered as a new clinical/histological entity.     

Oncogenic pathway of sporadic colorectal cancer with novel germline missense mutations in the hMSH2 gene

The deficiency of the DNA mismatch repair (MMR) system is involved in tumorigenesis of either familial or sporadic colorectal cancers showing microsatellite instability (MSI). To investigate the involvement of the mutated hMSH2 gene in carcinogenesis, we searched for alteration of the gene in 15 MSI tumors of Japanese patients with sporadic colorectal cancer by a polymerase chain reaction (PCR)-single strand conformation polymorphism (SSCP) and DNA sequencing analyses. We found 20 alterations including 7 novel mutations, 6 germline and one somatic. To assume an oncogenic pathway of tumor of two patients carrying germline missense mutations, G40S located in an evolutionarily conserved amino-terminal motif and Y619C in a domain interacting with either hMSH3 or hMSH6, somatic mutations in 9 target genes of the MMR defect and in the p53 and K-ras genes and loss of heterozygosity (LOH) at the hMLH1 and p53 gene loci were then studied. In the tumor carrying G40S, other somatic hMSH2 mutations, G203R and 687delA in the (A)(7) repeat, and 5 one-bp deletions in the target genes were found, while no mutation in the p53 and K-ras genes. These results indicate that G40S may affect the hMSH2 function and the tumor may be developed by a typical MSI pathway. In another tumor with Y619C, LOH at the hMLH1 gene locus, no mutation in MMR target genes, and two-hit inactivation of the p53 gene were detected. This MSI tumor seems to be developed by another than MSI pathway. These results indicate that there are different oncogenic pathways in the MSI sporadic colorectal cancers with germline missense mutations in the hMSH2 gene. We conclude that familial colorectal cancer-suspected cases exist in a small population of sporadic colorectal cancers.     

Microsatellite instability at chromosome 8p in non-small cell lung cancer is associated with lymph node metastasis and squamous differentiation

Genetic alterations at chromosome arm 8p are associated with advanced disease and poor patient outcome in several types of malignant tumors. We studied the frequency of microsatellite instability (MSI) and loss of heterozygosity (LOH) at chromosome 8p in early stage non-small cell lung cancer (NSCLC) of 47 patients with stage I or II disease (25 squamous cell carcinomas and 22 adenocarcinomas). Microsatellite analysis was performed after laser microdissection using 5 polymorphic tetranucleotide microsatellite markers and 4 dinucleotide markers at chromosome 8p. A pentanucleotide repeat marker at the chromosomal locus 17p13.1 (TP53.Alu) was also analyzed. Expression of the mismatch repair (MMR) proteins hMSH2, hMSH6 and hMLH1 was evaluated by immunohistochemistry. Microsatellite instability (MSI) in at least 2 markers was detected in 9 of 47 patients (19.1%) and was predominantly found at tetranucleotide repeats. Sixteen of 47 (34.0%) NSCLC demonstrated LOH at chromosome 8p. All MSI-positive tumors showed normal expression of the MMR proteins. The presence of MSI at chromosome 8p was associated with lymph node metastasis (p=0.02), squamous differentiation (8/25; 32%-p=0.03), and the presence of LOH at the p53 locus (p=0.06). None of the other investigated clinical, pathologic or molecular factors correlated with MSI. Our study showed that an elevated MSI at selected tetranucleotide sequences (EMAST) on chromosome 8p is frequent in early stage squamous cell carcinomas of the lung with lymphatic spread. The tetranucleotide marker panel used in this study was able to indicate lymph node metastasis and high risk disease in patients with resectable squamous cell lung cancer.     

Genetic and clinical features of human pancreatic ductal adenocarcinomas with widespread microsatellite instability

The incidences of microsatellite instability (MSI) and underlying DNA mismatch repair (MMR) defects in pancreatic carcinogenesis have not been well established. We analyzed 100 sporadic and 3 hereditary pancreatic ductal adenocarcinomas for MSI, and high-frequency MSI (MSI-H) and low-frequency MSI (MSI-L) tumors were further analyzed for frameshift mutations of possible target genes and for promoter methylation and mutation of DNA MMR genes, including hMLH1, hMSH2, hMSH3, and hMSH6 genes. Among the 100 sporadic tumors, 13 (13%) were MSI-H, 13 (13%) were MSI-L, and 74 (74%) were microsatellite stable (MSS) tumors. All of the three hereditary tumors from hereditary nonpolyposis colorectal cancer (HNPCC) patients were MSI-H. MSI-H tumors were significantly associated with poor differentiation and the presence of wild-type K-RAS and p53 genes. Patients with MSI-H tumors had a significantly longer overall survival time than did those with MSI-L or MSS tumors (P = 0.0057). Frameshift mutations of hMSH3, hMLH3, BRCA-2, TGF-beta type II receptor, and BAX genes were detected in MSI-H tumors. Hypermethylation of the hMLH1 promoter was observed in 6 (46%) of the 13 sporadic MSI-H tumors but not in any of the 3 hereditary MSI-H tumors or 13 MSI-L tumors. All of the 3 HNPCC cases had germ-line hMLH1 mutation accompanied by loss of heterogeneity or other mutation in the tumor. Our results suggest that pancreatic carcinomas with MSI-H represent a distinctive oncogenic pathway because they exhibit peculiar clinical, pathological, and molecular characteristics. Our results also suggest the principal involvement of epigenetic or genetic inactivation of the hMLH1 gene in the pathogenesis of pancreatic carcinoma with MSI-H.     

Frameshift mutations at coding mononucleotide repeats of the hRAD50 gene in gastrointestinal carcinomas with microsatellite instability

Microsatellite instability (MSI) and frameshift mutations in genes containing nucleotide repeats have been reported in a subset of colorectal and gastric carcinomas. This study describes the analysis of MSI-positive colorectal (39 cases) and gastric carcinomas (36 cases) for the presence of frameshift mutations of the six genes known to be involved in DNA repair and containing mononucleotide repeats in their coding region. Our mutational study of the 75 MSI-positive tumors revealed frequent mutations in hRAD50 (23 cases, 31%), BLM (16 cases, 21%), and hMSH6 (16 cases, 21%); rare mutations in BRCA1 (1 case, 1%) and ATM (3 cases, 4%); and no mutation in NBS1. In contrast, no frameshift mutation was found in 60 MSI-negative colorectal and gastric carcinomas. The mutation of hRAD50, a gene that is involved in the response to cellular DNA damage and forms a complex with hMRE11 and NBS1, has not been reported previously. Our results suggest that frameshift mutations of hRAD50, BLM, and hMSH6 are selected and play a role in the tumorigenesis of colorectal and gastric carcinomas with MSI. The MSI targeting of the hRAD50 and BLM genes represents an additional link between MSI and DNA repair because alteration of these genes could accelerate defective DNA repair.     

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.     

Mutations in <Emphasis Type="Italic">TGFbeta-RII</Emphasis> and <Emphasis Type="Italic">BAX</Emphasis>mediate tumor progression in the later stages of colorectal cancer with microsatellite instability

Background  

Microsatellite instability (MSI) occurs in 15% of colorectal cancers (CRC). The genetic targets for mutation in the MSI phenotype include somatic mutations in the transforming growth factor beta receptor typeII (TGFbetaRII), BAX, hMSH3 and hMSH6. It is not clear how mutations of these genes mediate tumor progression in the MSI pathway, and the temporal sequence of these mutations remains uncertain. In this study, early stage CRCs were examined for frameshift mutations in these target genes, and compared with late stage tumors and CRC cell lines.     

Sporadic colorectal adenocarcinomas with high-frequency microsatellite instability

BACKGROUND: Widespread microsatellite instability (MSI) occurs in nearly 15% of sporadic colorectal cancers. Large bowel carcinomas with high-frequency MSI (MSI-H) (instability at > or = 30% of microsatellite loci) are believed to display distinctive pathologic features and to behave less aggressively than microsatellite-stable (MSS) tumors and carcinomas with low-frequency MSI (MSI-L) (instability at < 30% of microsatellite loci). The aim of the current study was to accurately define the clinicopathologic and biologic features of MSI-H sporadic colorectal carcinomas. METHODS: MSI status was evaluated in 216 large bowel adenocarcinomas using polymerase chain reaction (PCR) and 6 microsatellite markers. Tumors that showed instability with at least two microsatellite markers were classified as MSI-H, whereas the other tumors were classified as MSI-L (instability at one locus) or MSS (no instability). Expression of p53, hMLH1, and hMSH2 gene products was determined by immunohistochemistry, and DNA ploidy pattern was determined by flow cytometry. The prognostic significance of MSI status was assessed by univariate and multivariate survival analyses. RESULTS: The significantly different pathologic features of MSI-H carcinomas were proximal location; large size; mucinous and medullary histotype; poor differentiation; expanding pattern of growth; more frequent Crohn-like conspicuous lymphoid reaction; and low incidence of extramural vein invasion. Most MSI-H tumors were DNA diploid (33 of 40 tumors; 82.5%) and p53 negative (34 of 44 tumors; 77.3%). Conversely, DNA aneuploidy and p53 overexpression were observed in 82.3% (130 of 158 tumors; P < 0.0001) and 54.1% (93 of 172 tumors; P = 0.0002) of MSI-L/MSS tumors, respectively. Loss of hMLH1 or hMSH2 expression was detected in a high fraction of MSI-H carcinomas (86. 0%). Patients with MSI-H tumors showed a better clinical outcome than patients with MSI-L/MSS tumors (P = 0.0017). Furthermore, in multivariate analysis that included conventional clinicopathologic parameters, MSI status, and p53 expression as covariates, MSI status was a significant independent prognostic indicator of disease specific survival. CONCLUSIONS: Assessment of MSI status is an essential step in the genetic characterization of large bowel carcinomas and identifies a subset of tumors with distinct clinical, pathologic, and biologic features.     

Assessment of markers for the identification of microsatellite instability phenotype in gastric neoplasms

We tested three mononucleotide, 45 dinucleotide, and five tetranucleotide repeats in 30 gastric adenomas and 30 gastric carcinomas for microsatellite instability (MSI) in order to evaluate which microsatellites might indicate the MSI status in gastric neoplasms. Along with the increase in tested markers, the proportion of low-frequency MSI (MSI-L) tumors increased. On immunohistochemistry, MSI-L gastric neoplasms did not show any alteration in hMLH1 or hMSH2 protein expression, while most of the high-frequency MSI (MSI-H) tumors did show alterations in the above mismatch repair proteins. The above findings suggested that MSI-L tumors cannot be distinguished from microsatellite stable tumors. Two mononucleotides, BAT25 and BAT26, were sufficient for the screening of MSI. An additional three dinucleotides, D17S786, D6S105 and D19S188, were also highly sensitive and specific in identifying MSI phenotype tumors.