Frequency Of Microsatellite Instability Research Articles

Mismatch repair protein loss and microsatellite instability in cholangiocarcinoma.

237 Background: Hereditary nonpolyposis colorectal cancer (HNPCC), or Lynch Syndrome, is an autosomal dominant syndrome characterized by mutations in genes involved in DNA mismatch repair (MMR) and consequent microsatellite instability (MSI). These genetic aberrations lead to an increased incidence of multiple malignancies including colorectal and endometrial cancer, among others. While an association between biliary tumors and HNPCC has been proposed, no published studies have documented MMR protein loss and MSI in a series of biliary tumor samples. After diagnosing cholangiocarcinoma (CCA) in two clinic patients known to have HNPCC and incidentally noting MMR protein loss and MSI in their tumor, we conducted an exploratory study to evaluate the frequency of MMR protein loss and MSI in patients with CCA. Methods: Discarded tissue samples from patients with CCA treated at the Massachusetts General Hospital (n=44) were evaluated for the loss of MLH1, PMS2, MSH2, and MSH6 with immunohistochemical staining. The results were correlated with clinicopathologic features, and the MSI status was collected from the medical record. Results: Four (9.1%) of 44 patients were found to have loss of at least two MMR proteins: 2 pts had MSH2/MSH6 loss, 1 had MLH1/PMS2 loss, and 1 had loss of all 4 proteins. Two patients had previously been tested for microsatellite instability and both were MSI-high. The clinicopathologic features of the 4 patients included: median age 54.5 yo; M:F 1:3; diagnosed with ≥ 1 HNPCC-related malignancy 1/4; family history of ≥ 2 HNPCC-related tumors 2/4, intrahepatic:extrahepatic CCA 3:1; moderately-poorly:poorly differentiated 2:2; T1:T2 3:1; ≥1 positive lymph node 1/4; lymphovascular invasion 2/3; perineural invasion 2/4. Conclusions: MMR protein loss was discovered in 9.1% of patients with CCA in this initial cohort. A second validation cohort from a different institution is currently being tested, and the results will be presented at the meeting. CCA may be an underappreciated co-morbid neoplasm in the spectrum of tumors for HNPCC. MMR protein loss should be further explored as a mechanism of oncogenesis in CCA, and clinicians should be aware of this malignancy in surveillance of patients with HNPCC.

Mutation at Intronic Repeats of the Ataxia-Telangiectasia Mutated (ATM) Gene and ATM Protein Loss in Primary Gastric Cancer with Microsatellite Instability

Ataxia-telangiectasia mutated (ATM) is a Ser/Thr protein kinase that plays a critical role in DNA damage-induced signaling and initiation of cell cycle checkpoint signaling in response to DNA-damaging agents such as ionizing radiation. We have previously reported the ATM protein loss by immunohistochemistry (IHC) in 16% of human gastric cancer (GC) tissue. We hypothesized that ATM gene intron mutations targeted by microsatellite instability (MSI) cause ATM protein loss in a subset of GC. We studied mononucleotide mutations at the intron of ATM gene, ATM IHC and MSI in GC. Ten human gastric cancer cell lines were studied for the ATM gene mutation at introns, RT-PCR, direct sequencing, and immunohistochemistry. GC tissues of 839 patients were analyzed for MSI and ATM IHC. Among them, 604 cases were analyzed for the ATM mutations at introns preceding exon 6, exon 10 and exon 20. Two human GC cell lines (SNU-1 and -638) showed ATM intron mutations, deletion in RT-PCR and direct sequencing, and ATM protein loss by IHC. The frequencies of ATM mutation, MSI, and ATM protein loss were 12.9% (78/604), 9.2% (81/882) and 15.2% (134/839), respectively. Analysis of associations among MSI, ATM gene mutation, and ATM protein loss revealed highly co-existing ATM gene alterations and MSI. ATM intron mutation and ATM protein loss were detected in 69.3% (52/75) and 53.3% (40/75) of MSI positive GC. MSI positivity and ATM protein loss were present in 68.4% (52/76) and 48.7% (37/76) of GC with ATM intron mutation. ATM mutation and ATM protein loss had characteristics of old age, distal location of tumor, large tumor size, and histologic intestinal type. Our study might be interpreted as that ATM gene mutation at intron might be targeted by MSI and lead to ATM protein loss in a selected group of GC.

Tracking the Molecular Features of Nonpolypoid Colorectal Neoplasms: A Systematic Review and Meta-Analysis

Nonpolypoid colorectal neoplasms (NP-CRNs) are proposed as a major contributor to the occurrence of interval cancers, but their underlying biology remains controversial. We conducted a systematic review and meta-analysis to clarify the major biological events in NP-CRNs. We systematically searched for studies examining molecular characteristics of NP-CRNs. We performed random effect meta-analyses. We measured the heterogeneity among studies using I(2) and possible publication bias using funnel plots. Fifty-three studies on KRAS, APC, or BRAF mutations, microsatellite instability (MSI), CpG island methylator phenotype (CIMP), or DNA promoter hypermethylation were included. We observed less KRAS mutations (summary odds ratio (OR) 0.30, confidence interval (CI)=0.19-0.46, I(2)=77.4%, CI=70.1-82.9) and APC mutations (summary OR 0.42, CI=0.24-0.72, I(2)=22.6%, CI=0.0-66.7) in NP-CRNs vs. protruded CRNs, whereas BRAF mutations were more frequent (summary OR 2.20, CI=1.01-4.81, I(2)=0%, CI=0-70.8), albeit all with large heterogeneity. Less KRAS mutations were especially found in NP-CRNs subtypes: depressed CRNs (summary OR 0.12, CI=0.05-0.29, I(2)=0%, CI=0-67.6), non-granular lateral spreading tumors (LSTs-NG) (summary OR 0.61, CI=0.37-1.0, I(2)=0%, CI=0-74.6), and early nonpolypoid carcinomas (summary OR 0.11, CI=0.06-0.19, I(2)=0%, CI=0-58.3). MSI frequency was similar in NP-CRNs and protruded CRNs (summary OR 0.99, CI=0.21-4.71, I(2)=70.3%, CI=38.4-85.7). Data for promoter hypermethylation and CIMP were inconsistent, precluding meaningful conclusions. This meta-analysis provides indications that NP-CRNs are molecularly different from protruded CRNs. In particular, some subtypes of NP-CRNs, the depressed and LST-NG, are featured by less KRAS mutations than polypoid CRNs. Prospective, multicenter studies are needed to clarify the molecular pathways underlying nonpolypoid colorectal carcinogenesis and potential implications for surveillance intervals.

Abstract 1216: Analysis of genetic aberrations in squamous cell carcinoma of the oral tongue.

Abstract Squamous cell carcinoma of the oral tongue (SCCOT) is a common form of head and neck squamous cell carcinoma (HNSCC). In the last few decades, a steady increase in incidence rates of SCCOT has been reported across the world including India. SCCOT is known to be an age related disease and tobacco consumption is implicated as the main etiological agent, like other HNSCC subtypes. Recent reports have indicated an increase in incidence of SCCOT in the young and in nonsmokers. Among HNSCC, SCCOT appears to be more aggressive with respect to its clinical and biological behavior. Molecular genetic studies on SCCOT are scarce and most studies have been conducted on a small cohort of patients and/or restricted to a single/few molecular marker(s). We have conducted a multipronged molecular genetic study of SCCOT and analyzed the status of known tumorigenesis pathways including TP53, epidermal growth factor receptor (EGFR), microsatellite instability (MSI), CDKN2A, FHIT and human papilloma virus (HPV) infection in surgically resected primary tumor samples and correlated with clinocopathological variables. 67% (67/100) of SCCOT samples exhibited p53 nuclear stabilization whereas a greater proportion (87/100; 87%) exhibited elevated EGFR expression, in accordance with existing literature. Interestingly, p53 nuclear stabilization was found to be more common in young (31/39; 79.5%) than in older (35/59; 59.3%) patients (p = 0.0481). As expected, patients with p53 nuclear stabilization exhibited poorer survival. Further, PCR based mutation screening of exons 5-8 of TP53 (encoding the DNA binding domain) revealed mutations in 50% of samples exhibiting nuclear stabilization. HPV infection was observed in 11/82 (13.4%) tumors while the frequencies of MSI (12/86; 14%) and loss of heterozygosity (LoH) in CDKN2A (32.6%) and FHIT (28.4%) loci were significantly higher than previous studies. In addition, LoH at FHIT locus was significantly associated with p53 nuclear stabilization (p=0.047). Analysis of genome-wide DNA copy number alterations (CNA) using array based comparative genomic hybridization revealed unique copy number alterations validated by quantitative PCR. Exome sequencing and transcriptome profiling are currently underway to understand the pathways/genes deregulated in SCCOT, especially in samples not exhibiting p53 nuclear stabilization. Citation Format: Raju Sr Adduri, Viswakalyan Kotapalli, Neha Ak Gupta, Swarnalata Gowrishankar, Mukta Srinivasulu, Subramanyeshwar Rao, Shantveer G. Uppin, Umanath Karopadi Nayak, Mohana Vamsy Chigurupati, Sujith Chayu Patnaik, NarasimhaRaju Kalidindi, Murali D. Bashyam. Analysis of genetic aberrations in squamous cell carcinoma of the oral tongue. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 1216. doi:10.1158/1538-7445.AM2013-1216

Analysis of microsatellite instability and loss of heterozygosity in ovarian cancer: a study in the population of Espírito Santo, Brazil

Ovarian cancer is currently the most lethal gynecological malignancy in women. It is a heterogeneous and cytogenetically complex disease previously associated with genomic instability. Our purpose was to analyze microsatellite markers to determine patterns and levels of instability as well as possible correlations with histopathological parameters. Polymerase chain reaction was used to characterize microsatellite instability (MSI) and loss of heterozygosity (LOH) in 24 ovarian tumors at 12 microsatellite loci. A total of 11 samples displayed MSI or LOH. Only low-level MSI was found. Markers D5S346 and CYP11 showed the highest MSI and LOH frequencies. D17S250 LOH was significantly associated with tumor histological type (P = 0.0003), and estrogen receptor α was also associated with tumor histological type (P = 0.048) when a combined analysis of LOH and MSI was performed. Furthermore, LOH was observed in a greater number of markers compared with those displaying MSI. Thus, our results support that MSI is less common than LOH in ovarian cancers.

Frequent microsatellite instability in papillary and solid-type, poorly differentiated adenocarcinomas of the stomach

Microsatellite instability (MSI) has been observed in 8-39 % of sporadic gastric cancers. However, despite numerous reports indicating a significant relationship between intestinal-type histology and MSI, detailed correlation between histological subtypes and MSI remains obscure. The purpose of the present study is to clarify the relationship between histological subtype and microsatellite status in gastric carcinomas. Microsatellite status was examined for 464 consecutive gastric carcinomas from 420 patients as well as histological subtypes and other clinicopathological findings. MSI was observed in 82 carcinomas (17.7 %), and the greatest proportions were observed in solid-type, poorly differentiated adenocarcinoma (43.0 %) and papillary adenocarcinoma (32.5 %), both being significantly higher than those of other subtypes. The proportion increased with advancing age (0 % at 51-64 years, 8.5 % at 65-74 years, 18.4 % at 75-84 years, 35.3 % at 85-96 years). Compared with microsatellite-stable carcinomas, microsatellite-unstable carcinomas were significantly related with older age, female gender, antral location, and predominant papillary adenocarcinoma and solid-type, poorly differentiated adenocarcinoma. Poorly differentiated type carcinoma was significantly less frequent than differentiated type in microsatellite-unstable cancer at the early stage, whereas no significant difference existed at the advanced stage. These results suggest that there are specific histological subtypes with highly frequent MSI and that gastric carcinoma with MSI originates from differentiated-type carcinomas, indicating histological diversity during tumor growth.

Analysis of genome instability in breast cancer

Breast cancer is a heterogeneous disease, previously associated with genomic instability. Our aim was to analyze microsatellite markers in order to determine patterns and levels of instability, as well as possible correlations with histopathological parameters. Polymerase chain reaction was used to characterize microsatellite instability (MSI) and loss of heterozygosity (LOH) in 107 breast carcinomas at twelve microsatellite loci. Some of the markers were selected because of their relation to steroid hormone metabolism, which seems to be related to sporadic breast cancer risk. D5S346 and D17S250 markers showed a statistically significant frequency of MSI. LOH in D3S1611, D17S250, AR and ER-β were associated with some parameters of worse prognosis. Marker group analysis showed that CYP19, AR and ER-β were related to histological grade III, ER-negative and PR-negative cases. Our results suggest that marker group analysis may be preferred to the single marker strategy, being predictive of worst prognosis when single markers are unable to provide such information. A further evaluation of steroid metabolism genes and their association with low penetrance genes in breast cancer may be useful.

Expression of the MAP kinase phosphatase DUSP4 is associated with microsatellite instability in colorectal cancer (CRC) and causes increased cell proliferation

DUSP4 (MKP-2), a member of the mitogen-activated protein kinase phosphatase (MKP) family and potential tumor suppressor, negatively regulates the MAPKs (mitogen-activated protein kinases) ERK, p38 and JNK. MAPKs play a crucial role in cancer development and progression. Previously, using microarray analyses we found a conspicuously frequent overexpression of DUSP4 in colorectal cancer (CRC) with high frequent microsatellite instability (MSI-H) compared to microsatellite stable (MSS) CRC. Here we studied DUSP4 expression on mRNA level in 38 CRC (19 MSI-H and 19 MSS) compared to matched normal tissue as well as in CRC cell lines by RT-qPCR. DUSP4 was overexpressed in all 19 MSI-H tumors and in 14 MSS tumors. Median expression levels in MSI-H tumors were significantly higher than in MSS-tumors (p < 0.001). Consistently, MSI-H CRC cell lines showed 6.8-fold higher DUSP4 mRNA levels than MSS cell lines. DUSP4 expression was not regulated by promoter methylation since no methylation was found by quantitative methylation analysis of DUSP4 promoter in CRC cell lines neither in tumor samples. Furthermore, no DUSP4 mutation was found on genomic DNA level in four CRC cell lines. DUSP4 overexpression in CRC cell lines through DUSP4 transfection caused upregulated expression of MAPK targets CDC25A, CCND1, EGR1, FOS, MYC and CDKN1A in HCT116 as well as downregulation of mismatch repair gene MSH2 in SW480. Furthermore, DUSP4 overexpression led to increased proliferation in CRC cell lines. Our findings suggest that DUSP4 acts as an important regulator of cell growth within the MAPK pathway and causes enhanced cell growth in MSI-H CRC.

Gastrointestinal cancers reactive for the PAb416 antibody against JCV/SV40 T-Ag lack JCV DNA sequences while showing a distinctive pathologic profile

AimImmunohistochemical and molecular studies have suggested an oncogenic role for JCV in gastrointestinal carcinomas, but at least in colorectal cancers, the data are far from being unambiguous.MethodsTwo large series of...

Microsatellite instability in Marek’s Disease Virus infected primary chicken embryo fibroblasts

BackgroundMarek’s disease virus (MDV), an oncogenic α-herpes virus, causes a devastating disease in chickens characterized by development of lymphoblastoid tumors in multiple organs. Microsatellite instability (MSI), a symptom of defect in DNA mismatch repair function, is a form of genomic instability frequently detected in many types of tumors. However, the involvement of MSI in MDV-infected cells has not been investigated. In this study, we determined the presence and frequency of MSI in primary chicken embryo fibroblasts infected with or without MDV strain in vitro.Results118 distinct microsatellite markers were analyzed by polymerase chain reaction (PCR) in 21 samples. MSI was found in 91 of 118 markers, and 12 out of 118 demonstrated frequency of MSI at ≥ 40%. 27 of 118 microsatellite loci did not show microsatellite instability.ConclusionsThese findings showed that MSI was a real event occurring in primary chicken embryo fibroblasts infected with MDV in vitro as evidenced by the high frequency of MSI, and may be specifically associated with genome alteration of host cells during MDV infected.

LARP7 is a potential tumor suppressor gene in gastric cancer

We previously reported frequent truncating mutations of the RNA-binding protein gene, La ribonucleoprotein domain family, member-7 (LARP7) in gastric cancers (GCs) with frequent microsatellite instability. LARP7 negatively regulates positive transcription elongation factor-b (p-TEFb) by binding to and stabilizing 7sk RNA. p-TEFb has been linked to proliferation and de-differentiation in various tissues. Therefore, we reasoned that loss of LARP7 may contribute to gastric tumorigenesis. In this study, we evaluated LARP7 mRNA expression in 18 GCs, their corresponding non-neoplastic gastric tissues (NGC), and 18 normal gastric tissues from healthy individuals (NN). We also assessed the effects of transient small interfering (siRNA)-mediated LARP7 knockdown in immortalized non-neoplastic gastric epithelial cells. LARP7 mRNA was significantly decreased in GCs (median 2.5) relative to NNs (median 14.9, P<0.01) as well as relative to their corresponding NGCs (median 8.1, P<0.01). Transfection of an siRNA directed against LARP7 (anti-LARP7 siRNA) into non-neoplastic gastric epithelial cells decreased 7sk levels by 72% relative to a control siRNA (P<0.01). Furthermore, anti-LARP7 siRNA transfection increased cell proliferation by 23% (P<0.01) and cell migration by 22% (P<0.001) relative to control siRNA transfection. Taken together, these findings suggest that LARP7 downregulation occurs early during gastric tumorigenesis and may promote gastric tumorigenesis via p-TEFb dysregulation.

Evaluation of microsatellite instability in women with epithelial ovarian cancer

The function of microsatellite instability (MSI) and the optimal panel of markers for epithelial ovarian cancer (EOC) are not well established. This study aimed to use the National Cancer Institute (NCI) markers BAT25, BAT26, D2S123, D5S346 and D17S250 to evaluate MSI in patients with ovarian serous cystadenocarcinoma, compared with ovarian serous cystadenoma and normal ovaries. A total of 37 patients were divided into three groups, as follows: cystadenocarcinoma (n=13), cystadenoma (n=10) and normal ovaries (n=14). DNA was extracted with TRIzol and quantified by spectrophotometry. MSI was evaluated by polymerase chain reaction (PCR), and classified as high (MSI-H), low (MSI-L) or stable (MSS). FIGO staging was I/II in 23.1% and III/IV in 76.9% of the cystadenocarcinoma group. Polymorphisms were found using at least one marker in 32 women, and were observed with D2S123 (83.7%), D17S250 (81.1%), D5S346 (72.9%), BAT25 (21.6%) and BAT26 (16.2%) markers. In the cystadenocarcinoma group, BAT25, BAT26, D2S123, D5S346 and D17S250 markers were positive in 30.8, 76.9, 53.8, 69.2 and 69.2% of patients, respectively. The same markers were positive in 30, 50, 40, 60 and 30% of the cystadenoma group, and 50, 71.4, 71.4, 64.3 and 63.3% in the normal ovary group, respectively. MSI-H was present in 84.6, 60 and 78.6% of the cystadenocarcinoma, cystadenoma and normal patients, respectively. MSI-L was detected in 0, 30 and 7.1%, and MSS was identified in 15.4, 10 and 14.3% of the cystadenocarcinoma, cystadenoma and normal patients, respectively. The frequency of MSI in both benign epithelial ovarian neoplasms and in normal ovaries was high, as well as in EOC, with no statistically significant difference between the groups. This suggests that MSI may arise as a consequence of the ovulatory process, and not solely as a feature of malignant ovarian tumors.

Prognostic significance of KRAS and BRAF mutations in Japanese patients with colorectal cancer.

e14033 Background: Recent evidence highlights the potential prognostic and predictive value of BRAF and K-RAS gene alterations in patients with colorectal cancer. To determine whether differences exist in the molecular mechanisms driving colorectal cancer between Japanese and Western, we characterized Japanese patients with colorectal cancer by assessing genetic alterations involved in cancer progression and response to treatment. Methods: We retrospectively evaluated 254 Japanese diagnosed with colorectal cancer at our institution between 1994 and 2009. Mutations in KRAS codons 12 and 13 and BRAF codon 600 were identified by direct sequencing. Microsatellite instability (MSI) status was determined by genotyping in the 5 loci. Associations between KRAS or BRAF mutation and clinicopathological characteristics and prognosis were evaluated. Results: KRAS and BRAF mutation were detected in 33.5% and 6.7% of all patients, respectively. KRAS mutation was correlated with poor recurrence free survival (RFS) (p = 0.03), especially in stage II patients (p = 0.007). BRAF mutation was significantly correlated with the anatomical site of tumor (p &lt; 0.001), tumor grade (p = 0.001) and high frequency of microsatellite instability (p &lt; 0.001). BRAF mutation was also correlated with poor overall survival in all cases of patients (p = 0.009). Overall, the background of KRAS and BRAF mutation was almost similar between CRCs of Western countries and those of Japanese. However, KRAS mutation status was considered to be helpful to predict recurrence in Japanese patients with stage II CRC. Conclusions: Our findings indicate that BRAF and K-RAS mutation plays an important role in the tumorigenesis of colorectal cancer. These results indicate that molecular analysis for BRAF and K-RAS may be a useful biomarker for identifying patients with right-sided colon cancer with poor outcome who may benefit from a more individualized course of therapy.

BRAF Mutations in Colorectal Cancer Are Associated With Distinct Clinical Characteristics and Worse Prognosis

Colorectal cancer is a heterogeneous disease with multiple underlying genetic mutations causing different clinical phenotypes. Mutation in the BRAF oncogene is a key step in malignant transformation within the methylator pathway to colorectal cancer. However, there is a paucity of information about BRAF mutant colorectal tumors. This study defines the clinical characteristics and oncologic outcome associated with colorectal cancer BRAF mutations. Colorectal adenocarcinomas from a single-institution frozen-tumor biobank were studied. Genomic DNA was isolated and analyzed for mutations in the BRAF oncogene by polymerase chain reaction amplification followed by direct sequencing. A sample was classified as mutant if any of the tested loci were mutated. Patient and tumor characteristics were recorded including patient age, sex, tumor location, tumor differentiation, and microsatellite instability. Statistical associations with BRAF mutant tumors were determined by the Fisher exact probability test, χ test, or Wilcoxon analysis. Kaplan-Meier estimates and multivariate Cox regression analysis were performed for overall survival. Four hundred seventy-five colorectal adenocarcinomas were included in the study population; 56 samples harbored a BRAF mutation (12%). There were significant differences between BRAF wild-type and mutant tumors in age (66 vs 75 years, p = 0.004), female sex (44% vs 71%, p < 0.001), proximal tumor location (44% vs 95%, p < 0.001), and frequency of microsatellite instability (16% vs 76%, p < 0.001). There was no difference in cancer stage between BRAF mutant and wild-type populations. Survival data were analyzed for 322 patients with stage I to III disease, and patients with a BRAF mutation had decreased overall survival than those without a mutation (p = 0.018). With the use of Cox regression analysis, BRAF mutation conferred a worse overall survival (HR 1.79, CI 1.05-3.05, p = 0.03) independent of microsatellite instability status. BRAF mutations in colorectal cancers are associated with distinct clinical characteristics and worse prognosis.

Molecular Analysis of Colorectal Tumors within a Diverse Patient Cohort at a Single Institution

African American colorectal cancer patients have worse survival outcomes than Caucasian patients. To determine whether differences exist in the molecular mechanisms driving colorectal cancer between African Americans and Caucasians, we characterized patient tumors from a single institution by assessing genetic alterations involved in colorectal cancer progression and response to treatment. We retrospectively examined 448 African Americans and Caucasians diagnosed with colorectal cancer at The University of Chicago Medical Center between 1992 and 2002. Microsatellite instability (MSI) status was determined by genotyping the BAT25, BAT26, BAT40, D5S346, and BAX loci. Mutations in KRAS codons 12 and 13 and BRAF codon 600 were identified by direct sequencing. MSI and detected mutations were correlated with clinicopathologic features. Overall, no difference existed in MSI or BRAF mutation frequencies between African Americans and Caucasians. However, African Americans with microsatellite stable (MSS)/MSI-low (MSI-L) tumors had a higher proportion of KRAS mutations than Caucasians (34% vs. 23%, P = 0.048) that was isolated to proximal colon cancers and primarily driven by mutations in codon 13. There was no racial difference in receipt of chemotherapy, but African Americans with MSS/MSI-L tumors had a 73% increased risk of death over Caucasians that could not be explained by known prognostic factors. The significantly higher risk of death among African Americans with MSS/MSI-L tumors may be related to differences in the distribution of factors influencing response to standard therapies. These data underscore the need for further research into the molecular mechanisms driving colorectal cancer progression in underserved and understudied populations.

Mapping of Microsatellite Instability in Endoscopic Normal Colon

Genomic instability in colorectal cancer (CRC) occurs as either microsatellite instability (MSI) or chromosomal instability. The present study was aimed at examining the MSI for the MLH1 and MSH2 genes in normal colon and polyps, if detected. Four segments of the colon were sampled in 102 subjects during colonoscopy. DNA samples were analyzed for the MSI status according to the Bethesda consensus panel. Family history of any type of cancer or for colon cancer was present in 44.8% and 9.4% of the individuals, respectively. Forty-eight percent of individuals were microsatellite stable for all five markers at all locations, 20% had low MSI status (MSI-L), and 32% had high MSI status (MSI-H). The frequencies of MSI markers differed significantly from each other (p=0.003). The most frequent positive marker was D17S250. This is the first study which revealed that MSI is present in endoscopically normal-looking colon of normal individuals and, more frequently, in individuals with family histories of CRC. The detection of very early-stage CRC is possible by MSI analysis of DNA mismatch repair genes in colon tissues. This study has revealed crucial information for the use of molecular tests in CRC screening, such as high frequencies of MSI in endoscopically normal colon, which might cause false positivity.

Genetic instability and CpG methylation in the 5'-flanking region of the PAI-1 gene in Chinese patients with gastric cancer

We explored a possible correlation of genetic instability and CpG methylation in the 5'-flanking region of the PAI-1 gene with clinicopathologic features of gastric cancer in Chinese patients and looked for molecular markers for diagnosing gastric tumor development. Microsatellite instability and loss of heterozygosity of the PAI-1 gene locus D7S515, D7S471 and pai-1 in 50 specimens of gastric cancer and relevant pericancerous tissues were detected by PCR-single strand conformation polymorphism (PCR-SSCP) with sliver staining. Methylation-specific PCR was used to detect CpG methylation in the 5'-flanking region of the PAI-1 gene. Microsatellite instability was significantly more common in the negative than in the positive serosa infiltration group of gastric cancer (42.86 vs 2.33%). The frequency of microsatellite instability was significantly lower in the cases with lymph node metastasis than in those without metastasis (18.18 vs 2.56%); however, it was significantly higher in the low differentiation group than that in the middle or high differentiation groups (21.05 vs 0.00%). CpG methylation in the 5'-flanking region of the PAI-1 gene did not differ significantly. Microsatellite instability and loss of heterozygosity of the PAI-1 gene apparently regulates the development of gastric cancer through different pathways. Microsatellite instability could be used as a molecular marker for the development of gastric cancer. CpG methylation in the 5'-flanking region of the PAI-1 gene appears not to be involved in the development of gastric cancer.

Loss of Expression of DNA Mismatch Repair Proteins Is Rare in Pancreatic and Small Intestinal Neuroendocrine Tumors

Two recent studies have identified a high rate of microsatellite instability (MSI) in pancreatic neuroendocrine tumors (pNETs). Microsatellite instability is rare in small intestinal neuroendocrine tumors (NETs). It is unclear why there is discordance in the frequency of MSI in the 2 studies of pNETs and why this mechanism is comparatively rare in small intestinal tumors. Loss of expression of DNA mismatch repair (MMR) proteins, which is known to correlate strongly with MSI, is not well studied in pancreatic or small intestinal NETs. To determine if there is loss of expression of MMR protein expression in pancreatic or small intestinal NETs. Sixty-nine patients (31 male, 38 female; mean age, 59.2 years) were identified who had a resection for a primary pancreatic (n = 35) or primary small intestinal (n = 34) NET during an 18-year period. Immunohistochemical stains for MLH1, MSH2, MSH6, and PMS2 were applied to archived tissue from all cases. All pNETs with adequate tissue (n = 32) were also assessed by MSI analysis. There was preserved expression of MLH1, MSH2, MSH6, and PMS2 in all 35 pNETs. Of 32 pNETs tested by polymerase chain reaction, 28 were microsatellite stable and DNA did not amplify in 4. In 34 small intestinal NETs, 2 cases had indeterminate MLH1 and 1 case had indeterminate PMS2 expression. The remainder had intact MMR protein expression. Defects in DNA MMR proteins are rare in pancreatic and small intestinal NETs, raising doubt that MSI plays a significant role in the pathogenesis of these tumors.

Microsatellite instability in young patients with sporadic colorectal adenomas.

This study was designed to determine the prevalence of microsatellite instability (MSI) among colorectal adenomas detected in patients ≤ 40 years of age and to compare the prevalence of MSI in young (≤ 40 years) and older (>40 years) patients with colorectal adenomas. Additionally, we attempted to identify the underlying cause of MSI in these patients. We prospectively tested for the presence of MSI using five NCI markers in samples from the two patient groups. The frequency of MSI was compared and the underlying causes of MSI were determined by methylation specific PCR and germ-line mutation analysis for mismatch repair genes. The frequency of MSI was higher in the ≤ 40 group than the >40 group (31.4% and 6.4%, respectively, p=0.0004). The MSI-high pattern was also more prevalent in the ≤ 40 group than the >40 group (15.7% and 2.5%, respectively, p=0.014). The hypermethylated hMLH1 gene was demonstrated in 7/8 (87.5%) patients with MSI-high in the ≤ 40 group and in 1/2 (50.0%) patients with MSI-high in the >40 group. No study subject showed a germline mutation of hMLH1 or hMSH2. MSI-high was more frequent in young (≤ 40 years) patients with colorectal adenoma than in older (>40 years) patients. Hypermethylation of the hMLH1 gene appears to be an important cause of MSI-high in these patients.

Assessment of the beneficial loci and prognostic implications of microsatellite instability in gastric carcinoma

Microsatellite instability (MSI) is a hyper-mutable phenotype caused by the loss of DNA mismatch repair activity, and plays a crucial role in gastric carcinogenesis. To clarify the role of genetic instability in relation to clinicopathological variables, and to identify predictive MSI markers that facilitate the early detection and improve the classification of gastric carcinomas (GCs), 13 microsatellite (MS) loci, including the National Cancer Institute (NCI) panel of MS markers (D2S123, D5S346, D17S250, BAT25 and BAT26) and 8 dinucleotide repeats (D3S1260, D5S107, D5S409, D17S261, D17S520, D17S855, D18S34 and D18S61) were studied in GC patients. MSI was found in 88.2% (30/34) of GC cases and the number of high-frequency MSI (MSI-H, 23.5%, 8/34), low-frequency MSI (64.7%, 22/34), and stable MSI (11.8%, 4/34), was calculated. Among the MS loci analyzed, D18S34 and D17S261 (15/34, 44.1%) exhibited the highest frequency of MSI, followed by D2S123 (14/34, 41.2%), D5S107, D5S346, D5S409 and D18S61 (12/34, 35.3%) (MSI>35%). MSI-H was particularly prevalent in older patients and was mainly found in the antrum and poorly differentiated tumors. Furthermore, MSI-H was significantly associated with lymph node involvement cases in females. One notable finding in this analysis was that the markers, D17S250 and D17S520, exhibited a significantly higher percentage of MSI in advanced gastric carcinomas than in early gastric carcinomas (P=0.046 and 0.046, respectively), and the D17S520 and BAT26 loci represented significant different correlations between the tumor stages (P=0.038 and 0.042, respectively). This study indicates that the novel markers, D18S34 and D17S261, perform more favorably than the NCI panel for the detection of MSI, and the D17S520 locus presents a potential target for predicting the clinical impact of GC. These novel MS loci may prove to be beneficial and independent tools for the construction of a comprehensive genetic classification for GC cases.