Mutational analysis of TTK gene in gastric and colorectal cancers with microsatellite instability

PURPOSE

The TTK gene plays a crucial role in regulation of the mitotic checkpoint. The TTK gene has an A9 mononucleotide repeat in the coding sequences, which harbors mutations in gastric (GC) and colorectal cancers (CRC) with microsatellite instability (MSI). However, there are three more repeats (the A7s) in the coding sequences that have not been analyzed. The aim of this study was to explore whether the three A7s as well as the A9 are altered in GC and CRC, and to find any association of TTK mutation with clinocopathologic characteristics of GC and CRC.

MATERIALS AND METHODS

We analyzed exon 5 (A7 and A7) and exon 22 (A9 and A7) which have repeat sequences in 30 GC with high MSI (MSI-H), 15 GC with low MSI (MSI-L), 35 CRC with MSI-H, and 15 CRC with MSI-L, by single-strand conformation polymorphism (SSCP) and DNA sequencing assays.

RESULTS

Overall, we detected 23 frameshift mutations in the repeat sequences of TTK in the GC with MSI-H (11/30; 36.7%) and the CRC with MSI-H (12/35; 34.3%), but not in the cancers with MSI-L. The mutations were observed in both A9 and A7 of exon 22, but in neither of the two A7s of exon 5. The mutations consisted of c.2560delA, c.2560dupA, c.2571delA and c.[2560delA(+)2571delA]. All of the mutations were frameshift mutations and would result in premature stops of TTK protein synthesis. There was no significant difference in clinopathologic parameters of the cancers with the mutations.

CONCLUSION

Our data indicate that frameshift mutations of TTK are common in both GC and CRC with MSI-H, and that the mutations occur not only in the A9 repeat but also in the A7 repeat. The data suggest that frameshift mutations of TTK might alter cell cycle control in the affected cells and contribute to pathogenesis of cancers with MSI-H.

Invasive front of colorectal cancer: Dynamic interface of pro-/anti-tumor factors

Tumor-host interaction at the invasive front of colorectal cancer represents a critical interface encompassing a dynamic process of de-differentiation of colorectal carcinoma cells known as epithelial mesenchymal transition (EMT). EMT can be identified histologically by the presence of “tumor budding”, a feature which can be highly specific for tumors showing an infiltrating tumor growth pattern. Importantly, tumor budding and tumor border configuration have generated considerable interest as additional prognostic factors and are also recognized as such by the International Union Against Cancer. Evidence seems to suggest that the presence of tumor budding or an infiltrating growth pattern is inversely correlated with the presence of immune and inflammatory responses at the invasive tumor front. In fact, several tumor-associated antigens such as CD3, CD4, CD8, CD20, Granzyme B, FOXP3 and other immunological or inflammatory cell types have been identified as potentially prognostic in patients with this disease. Evidence seems to suggest that the balance between pro-tumor (including budding and infiltrating growth pattern) and anti-tumor (immune response or certain inflammatory cell types) factors at the invasive front of colorectal cancer may be decisive in determining tumor progression and the clinical outcome of patients with colorectal cancer. On one hand, the infiltrating tumor border configuration and tumor budding promote progression and dissemination of tumor cells by penetrating the vascular and lymphatic vessels. On the other, the host attempts to fend off this attack by mounting an immune response to protect vascular and lymphatic channels from invasion by tumor buds. Whereas standard pathology reporting of breast and prostate cancer involves additional prognostic features, such as the BRE and Gleason scores, the ratio of pro- and anti-tumor factors could be a promising approach for the future development of a prognostic score for patients with colorectal cancer which could complement tumor node metastasis staging to improve the clinical management of patients with this disease.

Genetic and epigenetic characteristics of gastric cancers with JC virus T-antigen

AIM: To clarify the significance of JC virus (JCV) T-antigen (T-Ag) expression in human gastric cancer.

METHODS: We investigated the relationship between T-Ag detected by immunohistochemistry and Epstein-Barr virus (EBV) infection, microsatellite instability (MSI), and genetic and epigenetic alterations in gastric cancers. Mutations in the p53, β-catenin, KRAS, BRAF, PIK3CA genes were analyzed by polymerase chain reaction (PCR)-single strand conformation polymorphism and DNA sequencing. Allelic losses were determined by PCR at 7 microsatellite loci. Aberrant DNA methylation was analyzed by MethyLight assay.

RESULTS: JCV T-Ag protein expression was found in 49% of 90 gastric cancer tissues. T-Ag positivity was not correlated with clinicopathological characteristics. T-Ag expression was detected in a similar percentage of EBV positive cancers (4 of 9, 44%) and EBV negative cancers (35 of 73, 48%). T-Ag expression was detected in a significantly lower percentage of MSI-H cancers (14%) than in non MSI-H cancers (55%, P = 0.005). T-Ag expression was detected in a significantly higher percentage of cancers with nuclear/cytoplasmic localization of β-catenin (15 of 21, 71%) than in cancers without (42%, P = 0.018). p53 mutations were detected in a significantly lower percentage of T-Ag positive cancers (32%) than in T-Ag negative cancers (57%, P = 0.018). T-Ag positive gastric cancers showed a significant increase in the allelic losses and aberrant methylation compared with T-Ag negative gastric cancers (P = 0.008 and P = 0.003).

CONCLUSION: The results suggest that JCV T-Ag is involved in gastric carcinogenesis through multiple mechanisms of genetic and epigenetic alterations.

Checkpoint with forkhead-associated and ring finger promoter hypermethylation correlates with microsatellite instability in gastric cancer

AIM: To examine the methylation status of the promoter region of the checkpoint with forkhead-associated and ring finger (CHFR) and microsatellite mutator status in 59 primary gastric cancers.

METHODS: We investigated the promoter methylation of CHFR in 59 cases of gastric cancer using methylation-specific PCR. Five microsatellite loci were analyzed using high-intensity microsatellite analysis reported previously, and p53 gene mutations were investigated by direct sequencing.

RESULTS: Twenty cases (33.9%) showed promoter methylation and no relation was observed with the clinicopathological factors. We found that the promoter methylation of CHFR was frequently accompanied with microsatellite instability (MIN). Seven of 20 (35.0%) cases showed MIN in hypermethylation of the CHFR tumor, while three of 39 (7.7%) cases showed MIN in the non-methylated CHFR tumor (P < 0.01). However, we failed to find any relationship between CHFR methylation and p53 mutation status.

CONCLUSION: The coordinated loss of both the mitotic check point function and mismatch repair system suggests the potential to overcome the cell cycle check point, which may lead to an accumulation of mutations. However, the p53 mutation was not related to hypermethylation of the CHFR promoter and MIN, which indicates that an abnormality in p53 occurs as an independent process from the mismatch repair deficiency in carcinogenesis.

Detection of microsatellite instability in gastric cancer and dysplasia tissue in Lanzhou province of China

AIM: To investigate the relationship between microsatellite instability (MSI) and the gastric cancer and its effect on carcinogenesis in Lanzhou province of China.

METHODS: Silver staining single strand conformation polymorphis-polymerease chain reaction (PCR-SSCP) was used to screen MSI markers at 5 loci (Bat25, Bat26, D2S123, D5S346 and D17S250) in the DNA which were all extracted from gastric cancer (n = 43) and dysplasia (n = 21) tissues with Phenol-Chloroform method, in the same way as corresponding normal gastric tissues. MSI was analyzed in the gastric cancer and dysplasia.

RESULTS: MSI was detected in 28/43 cases of gastric cancer (65.1%) including 8 MSI-H (28.6%), and 20 MSI-L (71.4%). Six out of 21 cases were detected in dysplasia (28.6%), including 2 MSI-H (33.3%) and 4 MSI-L (66.7%).

CONCLUSION: The incidence of MSI in HEXI gastric cancer is very higher, probably contributive to the multistep gastric carcinogenesis. MSI may be a relatively better marker of gastric cancer.

Nuclear and mitochondrial microsatellite instability in colorectal cancer

AIM: To explore the roles of nuclear microsatellite instability (nMSI) and mitochondrial microsatellite instability (mtMSI) in the pathogenesis of colorectal cancer and their relationship.

METHODS: mtMSI was detected by using direct sequencing analysis, and nMSI by microsatellite scan method. Relationship between the positive incidence of mtMSI and nMSI was analyzed.

RESULTS: Forty cases with colorectal cancers were studied for mtMSI and nMSI. The mtMSI in at least one locus was detected in 11 out of 40 (27.5%) cases. Out of the 11 cases with mtMSI, 9 showed mtMSI at one locus (17.5%) and 2 at 11 loci (5%), but none at more than three loci. The nMSI at BAT25, BAT26 were detected in 9 out of 40 (22.5%) cases. mtMSI was found not to be associated with sex, age, subsite or TNM stage (P > 0.05). mtMSI was significantly correlated with nMSI (P < 0.05).

CONCLUSION: mtMSI may be involved in the carcinogenesis of some colorectal cancer, and mtMSI is associated with nMSI.

Changes of tumor suppressor gene PTEN and microsatellite instability in gastric cancer and precancerous lesion and their correlations

AIM: To investigate the changes of tumor suppressor gene PTEN and microsatellite instability (MSI) in gastric cancer and precancerous lesion as well as the relationship between them.

METHODS: Samples of gastric cancer and precancerous lesion were collected from endoscopy center and oncology surgery department of China Medical University. There were 30 cases in each group. PCR-SSCP silver staining was used to analyze the loss of heterozygosity (LOH) in PTEN gene and MSI. PTEN mutations were detected by PCR-SSCP and sequencing, and PTEN protein expression was detected by S-P immunohistochemistry.

RESULTS: The percentages of PTEN LOH in atrophic gastritis without intestinal metaplasia, atrophic gastritis with intestinal metaplasia, atypical hyperplasia, early-stage gastric cancer, and advanced gastric cancer were 10%, 10%, 13.3%, 20%, and 30%; meanwhile, the proportions of MSI were 13.3%, 16.7%, 23.3%, 36% and 40%, separately. The protein expression of PTEN in normal gastric mucosa was 100%, in chronic superficial gastritis, and it was 96.7%, 90.0%, 76.7%, 73.3%, 63.3%, 60.0% and 43.3% in chronic superficial gastritis, chronic atrophic gastritis without intestinal metaplasia, atrophic gastritis with intestinal metaplasia, moderate atypical hyperplasia, severe atypical hyperplasia, early-stage gastric cancer, and advanced gastric cancer, separately. PTEN mutation was detected in 3 cases, all of whom were found with advanced gastric cancer and positive for MSI.

CONCLUSION: Loss and mutation of PTEN gene are closely associated with the invasion and metastasis of gastric cancer. PTEN protein expresion is down-regulated during the pathogenesis of gastric cancer, and MSI is a early molecular marker in the pathogenesis of gastric cancer. PTEN mutation is commonly occurred in MSI-positive gastric cancer.

Fragile histidine triad gene alterations are not essential for hepatocellular carcinoma development in South Korea

AIM: To establish the role of FHIT in the pathogenesis hepatocellular carcinoma (HCC).

METHODS: We examined genomic alterations, as well as, mRNA and protein expression patterns from the FHIT gene, in 48 surgically resected hepatocellular carcinoma (HCC) tissues. Additionally, p53 mutations were analyzed.

RESULTS: Aberrant FHIT transcripts were detected in 11 of 48 surrounding non-tumor liver tissues and 27 of 48 HCC samples (22.9% vs 56.3%, P = 0.002). No point mutations were identified within the open reading frame region of FHIT. Loss of heterozygosity (LOH) of the FHIT locus was detected in 4 of 42 informative cases for D3S1300, and 3 of 29 informative cases for D3S1313. Reduced expression of FHIT protein (Fhit) was observed in 8 (16.7%) of 48 HCC samples, with complete loss of Fhit in only 1 case. There were no associations with abnormal transcripts, LOH, and Fhit expression. p53 mutations were identified in 9 of the 48 HCC cases. However, none of the cases displayed a G to T transversion at p53 codon 249.

CONCLUSION: Aberrant FHIT transcripts were more common in HCC tissues as compared to non-cancerous liver tissues. However, Fhit expression was lost or reduced in a minor fraction of HCC tissues, while it was strongly expressed in non-cancerous liver tissues. Therefore, our study suggests that FHIT plays a role in relatively few HCC cases in South Korea.

Frequent mutations of the CA simple sequence repeat in intron 1 of EGFR in mismatch repair-deficient colorectal cancers

AIM: To investigate the polymorphic simple sequence repeat in intron 1 of the epidermal growth factor receptor gene (EGFR) (CA-SSRI), which is known to affect the efficiency of gene transcription as a putative target of the mismatch repair (MMR) machinery in colorectal tumors.

METHODS: The CA-SSR I genotype was analyzed in a total of 86 primary colorectal tumors, selected upon their microsatellite instability (MSI) status [42 with high frequency MSI (MSI-H) and 44 microsatellite stable (MSS)] and their respective normal tissue. The effect of the CA-SSR I genotype on the expression of the EGFR gene was evaluated in 18 specimens using quantitative real-time reverse transcription PCR and immunohistochemistry.

RESULTS: Mutations in CA-SSR I were detected in 86% (36 of 42) of MSI-H colorectal tumors and 0% (0 of 44) of MSS tumors, indicating the EGFR gene as a novel putative specific target of the defective MMR system (P < 0.001). Impaired expression of EGFR was detected in most of the colorectal tumors analyzed [6/12 (50%) at the mRNA level and 15/18 (83%) at the peptide level]. However, no association was apparent between EGFR expression and CA-SSR I status in tumors or normal tissues.

CONCLUSION: Our results suggest that CA-SSRI sequence does not contribute to the regulation of EGFR transcription in colon, and should thus not be considered as a promising predictive marker for response to EGFR inhibitors in patients with colorectal cancer.

Genetic changes of p53, K-ras, and microsatellite instability in gallbladder carcinoma in high-incidence areas of Japan and Hungary

AIM: To disclose geographic differences in genetic changes involved in gallbladder carcinogenesis between two distinct high-incidence areas of Japan and Hungary.

METHODS: We examined 42 cases of gallbladder carcinoma: 22 Japanese and 20 Hungarian cases. p53 mutations at exons 5 to 8 and K-ras mutations at codon 12 were tested by direct sequencing. Microsatellite instability was determined from fluorescent dye-labeled PCR amplifications of five-microsatellite markers (BAT-25, BAT-26, D2S123, D5S346, and D17S250).

RESULTS: Mutations of p53 were detected in 11 of 22 Japanese cases and 6 of 18 Hungarian cases (11/22 vs 6/18, P = 0.348). Transition at CpG sites was found in none of 11 Japanese cases and 2 of 6 Hungarian cases; the difference was marginally significant (0/11 vs 2/6, P = 0.110). K-ras mutations were detected in only one of the Hungarian cases. Eight of 19 (42.1%) Japanese cases were MSI-high (presence of novel peaks in more than one of the five loci analyzed), whereas only 1 of 15 (6.7%) Hungarian cases was MSI-high (P = 0.047).

CONCLUSION: It appears that the p53 mutations and MSI differ in patients with gallbladder carcinoma between two distinct high-incidence areas. Geographic variation might exist in the process of gallbladder carcinogenesis.

Two novel germline mutations of MLH1 and investigation of their pathobiology in hereditary non-polyposis colorectal cancer families in China

AIM: To detect germline mutations of MLH1, and investigate microsatellite instability and expression of MLH1 in tumor tissues of hereditary non-polyposis colorectal cancer (HNPCC) with two novel germline mutations, and further investigate the pathobiology of the two novel mutations of MLH1.

METHODS: RNA was extracted from the peripheral blood of 12 patients from 12 different families that fulfilled the Amsterdam II Criteria for HNPCC. Germline mutations of MLH1 were determined by RT-PCR, followed by cDNA sequencing analysis. PCR-GeneScan analysis was used to investigate microsatellite instability with a panel of five microsatellite markers (BAT26, BAT25, D5S346, D2S123 and mfd15), along with immunohistochemical staining to detect the expression of MLH1 protein in two patients' tumor tissues with novel mutations.

RESULTS: Three germline mutations were found in four patients, one of the mutations has previously been reported, but the other two, CGC→TGC at codon 217 of exon 8 and CCG→CTG at codon 581 of exon 16, have not been reported. The two patients' tumor tissues with novel mutations had high-frequency microsatellite instability that showed more than two unstable loci, and both tumors lost their MLH1 protein expression.

CONCLUSION: The two novel germline mutations of MLH1 in HNPCC families i.e. CGC→TGC at codon 217 of exon 8 and CCG→CTG at codon 581 of exon 16, are very likely to have pathological significance.

Clinical prospects and research progress in hereditary non-polyposis colorectal cancer

Hereditary non-polyposis colorectal cancer (HNPCC), also called Lynch syndrome, is an autosomal-dominantly inherited disease and is associated with germline mutations in mismatch repair (MMR) genes and microsatellite instability (MSI). HNPCC is the most common form of hereditary colorectal cancer, accounting for 5%-15% of colorectal cancers. HNPCC has characteristic clinicpathological features, such as right-sided predominance, more synchronous or metachronous multiple primary colorectal cancer, young age at diagnosis, and poor histopathological differentiation. Recently, surgery has been the main means of treating HNPCC. However, COX-2 inhibitors may be a new therapeutic approach. Recent molecular biology studies have deepened our understanding of its the biological behavior and therapy.

Identification of Lynch syndrome: How should we proceed in the 21st century?

Lynch syndrome, also known as hereditary non-polyposis colorectal cancer (HNPCC), is the most common form of hereditary colorectal cancer. Although great advances in the understanding of its molecular basis have taken place in the last decade, optimal selection of individuals for HNPCC genetic testing remains controversial. This is especially relevant since colonoscopy has been proven effective for reducing colorectal cancer incidence and mortality in individuals at-risk for this disorder. In this manuscript, we summarize the most significant contributions to this important issue that have appeared in the last few years.

Telomerase activity in colorectal cancer, prognostic factor and implications in the microsatellite instability pathway

AIM: To determine whether the telomerase activity is related to the Microsatellite instability (MSI) genetic pathway and whether it means a difference in the survival.

METHODS: The population consisted of 97 colorectal cancer patients. MSI determination was performed in accordance with the NCI criteria using PCR and Genescan. Telomerase activity was determined by the TRAP-assay, an ELISA procedure based on the amplification of telomeric repeat sequences.

RESULTS: 6.2% showed high MSI (MSI-H), 10.3% showed low MSI (MSI-L) and 83.5% did not show this alteration (MSS). Positive telomerase activity was detected in 92.8% of the patients. 83.3% of MSI-H tumors showed positive telomerase against 93.8% of MSS tumors. In the overall survival analysis the absence of telomerase activity conferred a better prognosis.

CONCLUSION: Previous works have shown that tumors which develop via the MSI pathway present a better prognosis. No link between telomerase activity and MSI status is observed, although sample sizes are small. Patients with telomerase negative tumors had better overall survival than patients with telomerase positive tumors.

Serrated neoplasia of the colorectum

Serrated polyps of the colorectum form a group of related lesions which include aberrant crypt foci (ACF), conventional hyperplastic polyps, mixed (admixed) polyps, serrated adenomas and sessile serrated adenomas. In recent years the molecular differences between these morphologically similar lesions have been highlighted, and their differing biological potential has been realised. In particular, the sessile serrated adenoma has become recognised as the precursor lesion to a group of sporadic colorectal carcinomas characterised by morphological and molecular features distinct from conventional adenomas. These recent findings have challenged the long held paradigm that all colorectal carcinomas arise via the traditional adenoma-carcinoma sequence. In addition, they present a major challenge for the early detection and management of colorectal cancer, which is no longer regarded as a homogeneous entity.

Novel mutations and sequence variants in exons 3-9 of human T Cell Factor-4 gene in sporadic rectal cancer patients stratified by microsatellite instability

AIM: To establish the role of human T Cell Factor-4 (hTCF-4) gene exons 3-9 mutation status in association with sporadic rectal cancer with microsatellite instability (MSI).

METHODS: Microsatellite markers were genotyped in 93 sporadic rectal cancer patients. Eleven cases were found to be high-frequency MSI (MSI-H). Sequence analysis of the coding region of the exons 3-9 of hTCF-4 gene was carried out for the 11 MSI-H cases and 10 controls (5 microsatellite stability (MSS) cases and 5 cases with normal mucosa). The sequencing and MSI identification were used.

RESULTS: Several novel mutations and variants were revealed. In exon 4, one is a 4-position continuous alteration which caused amino acid change from Q131T and S132I (391insA, 392 G > A, 393 A > G and 395delC) and another nucleotide deletion (395delC) is present in MSI-H cases (5/10 and 4/10, respectively) but completely absent in the controls.

CONCLUSION: Novel mutations in exon 4 of hTCF-4 gene were revealed in this study, which might be of importance in the pathogenesis of sporadic rectal cancer patients with MSI-H.

Microsatellite instability in sporadic colorectal cancer and its relationship with clinicopathological features

AIM: To analyze the relationship between microsatellite instability (MSI) and clinicopatho-logical features in sporadic colorectal cancer and its clinical significance.

METHODS: Fluorescence multiplex polymerase chain reaction was used to detect the microsatellite instability with five microsatellite loci in 105 patients with sporadic colorectal cancer. The clinicopathological features characterized by microsatellite instability and microsatellite stability were compared statistically.

RESULTS: We found microsatellite instability in 24.7% of sporadic colorectal cancer patients, including 14 (13.3%) cases with MSI-high, 12 (11.4%) cases with MSI-low, and 79 (75.3%) cases with MS-stable (MSS). The instability of D5S346 was found in 6 cases (5.6%), BAT-26 in 9 (8.6%) cases, BAT-25 in 11 (10.5%) cases, D17S250 in 9 (8.6%) cases, and D2S123 in 11 cases (10.5%). The differentiation and lymph node metastasis status between MSI- and MSS-positive colorectal cancer was statistically different (P = 0.047, P = 0.029), but not the remaining variables (P > 0.05).

CONCLUSION: Low differentiation and metastasis are found in MSI-positive sporadic colorectal cancer, which may be one cause of a favorable survival.

Clinical and molecular analysis of hereditary non-polyposis colorectal cancer in Chinese colorectal cancer patients

AIM: To analyze the frequency of hereditary non-polyposis colorectal cancer (HNPCC) in Chinese colorectal cancer (CRC) patients, and to discuss the value of microsatellite instability (MSI) and/or immunohistochemistry (IHC) for MSH2/MLH1 protein analysis as pre-screening tests in China.

METHODS: The Amsterdam criteriaIandII(clinical diagnosis) and/or germline hMLH1/hMSH2 mutations (genetic diagnosis) were used to classify HNPCC families. Genetic tests, including microsatellite instability, immunohistochemistry for MSH2/MLH1 proteins and hMSH2/hMLH1 genes, were performed in each proband.

RESULTS: From July 2000 to June 2004, 1988 patients with colorectal cancer were analysed and 114 CRC patients (5.7%) from 48 families were categorized as having HNPCC, including 76 from 26 families diagnosed clinically and 38 from the other 22 families diagnosed genetically. The sensitivity and specificity of high MSI and IHC for predicting mutations were 100% and 54%, and 79% and 77%, respectively.

CONCLUSION: The frequency of HNPCC is approximately 10% among all Chinese CRC cases. The MSI and IHC detections for hMSH2/hMLH1 proteins are reliable pre-screening tests for hMLH1/hMSH2 germline mutations in families suspected of having HNPCC.

Relationship between Helicobacter pylori and DNA mismatch repair system

Helicobacter pylori infection causes the defect of mismatch repair (MMR) in eucaryotes, and microsatellite instability (MSI) in gastric epithelial cells, which increases the spontaneous mutation of relative genes, and finally results in the susceptibility to tumors in human bodies. DNA MMR can prevent the excessive proliferation of mutant cells and development of tumors by correcting mismatched bases, which occur in the process of duplication and recombination, and inducing apoptosis of the cells in which DNA had been seriously impaired. The majority of the mutation in mismatch repair gene is the gene mutation in which substitution exceeds the absence or insertion of the single basic group. In MMR, hMLH1 and hMSH2 gene are the main controlling genes. Current research showed that H pylori infection might lead to functional defect of MMR, which had played an important role in the development of gastric carcinomas. In this article, we reviewed the correlations between H pylori infection and DNA mismatch repair system.

Analysis of microsatellite instability in stool DNA of patients with colorectal cancer using denaturing high performance liquid chromatography

AIM: To evaluate the usefulness of denaturing high performance liquid chromatography (DHPLC) for analyzing microsatellite instability (MSI) status in stool DNA of patients with colorectal cancer.

METHODS: A total of 80 cancer tissues from patients with primary sporadic colorectal tumor (proximal cancer: 27, distal cancer: 53) and matched stool (which were employed for comparison with the tissues) were analyzed for MSI status in BAT 26. DNA samples extracted from stool were evaluated by nested polymerase chain reaction (PCR) and DHPLC for MSI analysis.

RESULTS: Six cases (7.5%) of MSI were identified in BAT 26 from 80 cancer tissues. All the stool DNA samples from patients whose cancer tissue showed MSI also displayed MSI in BAT 26.

CONCLUSION: As MSI is one of the established fecal DNA markers to screen colorectal cancer, we propose to use DHPLC for the MSI analysis in fecal DNA.

Role of detection of microsatellite instability in Chinese with hereditary nonpolyposis colorectal cancer or ordinary hereditary colorectal cancer

AIM: To detect microsatellite instability (MSI) in patients with hereditary nonpolyposis colorectal cancer or ordinary hereditary colorectal cancer and to provide criteria for screening the kindreds with hereditary nonpolyposis colorectal cancer at molecular level.

METHODS: MSI was detected in the specimens from 20 cases with HNPCC, 20 cases with ordinary hereditary colorectal cancer and 20 cases with sporadic colorectal cancer by means of polymerase chain reaction-single strand conformation polymorphism.

RESULTS: The positive rate of MSI was 85% (17/20) in HNPCC group, 40% (8/20) in ordinary hereditary colorectal cancer group and 10% (2/20) in the sporadic colorectal cancer group respectively. The differences were significant. The mean ages of the three groups were 43.6, 52.2, and 61.8 years respectively, which increased gradually. The incidence of right hemicolon cancer was 64.7%, 37.5%, and 0% respectively, which decreased gradually and had significant difference. The expression ratio of BAT26 and BAT25 was 94.1% respectively, which was highest in the 5 gene sites studied. The incidence of poorly differentiated adenocarcinoma was 70.6% in HNPCC group among high frequency microsatellite instability (MSI-H), which was higher than the other two groups, which had 50% and 50% respectively.

CONCLUSION: The incidence of MSI-H is higher in HNPCC group. The detection of MSI is simple and economical and has high correlation with the clinicopathologic feature of HNPCC and can be used as a screening method to detect the germ line mutation of the mismatch repair gene.

Prognostic significance of microsatellite alterations at 1p36 in cholangiocarcinoma

AIM: To investigate loss of heterozygosity (LOH) and microsatellite instability (MSI) on the chromosomal region 1p36-pter in cholangiocarcinoma (CCA) patients and determine the association between microsatellite alterations and clinicopathological parameters.

METHODS: Ten polymorphic microsatellite markers were determined for LOH and MSI using GS-3000 gel scan fragment autoanalyzer.

RESULTS: Sixty-eight out of 90 cases (75.6%) showed LOH in one or more loci. LOH was found most frequently at D1S199 (40.0%), D1S507 (34.6%), D1S2845 (30.5%), and D1S2734 (30.1%). MSI was found in 34 of 90 cases (37.8%) at one or more loci. Fine mapping at 1p36 showed two distinctive regions of common loss, which were D1S2845 and the 25.5-cM region between D1S507 and D1S2734, indicating the existence of putative tumor suppressor genes that is likely to play important roles in the development of CCA. Patients with LOH at D1S234 showed less lymphatic invasion (P = 0.017), whereas patients with LOH at D1S2676 exhibited more lymphatic invasion than those without (P = 0.031). LOH at D1S2845 showed a significant correlation with nerve invasion (P = 0.029). Moreover, patients who demonstrated MSI at D1S228 showed a poor prognosis (P = 0.0026).

CONCLUSION: Allelic loss plays a major role in microsatellite alterations at chromosome 1p36, which may contribute to carcinogenesis and pathogenesis of liver fluke related CCA and these alterations can be used as molecular prognostic indicators for CCA patients.

Genetic instability of BRCA1 gene at locus D17S855 is related to clinicopathological behaviors of gastric cancer from Chinese population

AIM: To investigate genetic instability of gene BRCA1 at locus D17S855, and their relationship with clinicopathological characteristics of gastric cancer in Chinese population.

METHODS: Microsatellite instability (MSI) and loss of heterozygosity (LOH) of gene BRCA1 at locus D17S855 were compared between 37 samples of gastric cancer and corresponding non-cancerous gastric tissue.

RESULTS: MSI at locus D17S855 was positive in 7 of 37 samples of gastric cancer (18.95%). MSI had a close relationship with TNM staging but no relation with lymph node metastasis, histological type or tumor differentiation. MSI positive frequency in TNM I + II (31.58%, 6/19) was much higher than that in TNM III + IV (5.56%, 1/18), (P < 0.05). LOH positive rate was 18.92% (7/37). LOH had no relationship to histological type, tumor differentiation or lymph node metastasis, but LOH positive rate in TNM III + IV was 33.33% (6/18)，much higher than that in TNM I + II ( 5.26%, 1/19), (P < 0.05). BRCA1 protein was expressed in 14 of 37 samples of gastric cancer. The positive rates of BRCA1 protein in TNM I + II and TNM III + IV were 57.89% and 16.67%, respectively, (P < 0.05). The positive rate of BRCA1 protein was 77.78% in high differentiation samples, 30.77% in middle differentiation and 12.50% in lower differentiation samples, (P < 0.05).

CONCLUSION: MSI of BRCA1 gene could be used as a molecular marker in early phases of sporadic gastric cancer in Chinese population. LOH occurs at later period of gastric cancer, therefore, it could be used as prognostic factor.

Tumor differentiation phenotype in gastric differentiated-type tumors and its relation to tumor invasion and genetic alterations

AIM: To clarify the relations between tumor differentiation phenotype and tumor invasion or genetic alterations in gastric differentiated-type tumors.

METHODS: We examined the tumor differentiation phenotype, the presence of mutations in APC and p53, and the microsatellite instability (MSI) status in 48 gastric adenomas and 171 differentiated-type carcinomas. The tumor differentiation phenotype was determined by examining the expression of human gastric mucin (HGM), MUC6, MUC2 and CD10. The tumors were then classified into gastric- (G-), gastric and intestinal mixed- (GI-), or intestinal- (I-) phenotypes, according to the immunopositivity of the above markers. The presence of mutations in APC and p53 and the MSI status were also investigated in all the tumors.

RESULTS: Gastric adenomas were significantly associated with CD10 expression, I-phenotype tumors and the presence of APC mutations, compared with carcinomas (66.7% vs 25.1%, P < 0.0001; 56.3% vs 14.6%, P < 0.0001; 39.6% vs 14.0%, P < 0.0001, respectively) and inversely associated with expressions of HGM and MUC6 and the presence of p53 mutations (10.4% vs 62.6%, P < 0.0001; 39.6% vs 64.3%, P = 0.003; 2.0% vs 26.3%, P = 0.001, respectively). The frequency of APC mutations was significantly higher in HGM-negative tumors, MUC6-negative tumors, CD10-positive tumors and I-phenotype tumors than in HGM-positive tumors, MUC6-positive tumors, CD10-negative tumors and G-phenotype tumors (32.7% vs 7.1%, P < 0.0001; 27.8% vs 14.0%, P = 0.0182; 37.3% vs 10.4%, P < 0.0001; and 38.5% vs 9.5%, P = 0.0017, respectively). The frequency of MSI was significantly higher in MUC6-positive tumors, CD10-negative tumors and G-phenotype tumors than in MUC6-negative tumors, CD10-positive tumors and I-phenotype tumors (24.8% vs 6.7%, P = 0.0009; 22.2% vs 8.0%, P = 0.0143; and 28.6% vs 9.6%, P = 0.0353, respectively).

CONCLUSION: The tumor differentiation phenotype is closely related to tumor invasion and genetic alterations in gastric differentiated-type tumors.

Microsatellite instability in gastric cancer and pre-cancerous lesions

AIM: To investigate the microsatellite instability (MSI) in cancer and pre-cancerous lesions of the stomach and its mechanisms underlying the development of gastric cancer.

METHODS: Thirty-six gastric cancer samples were obtained from patients undergoing surgery. Forty-one gastric mucosa samples with dysplasia and 51 with intestinal metaplasia (IM) were obtained from patients with chronic gastritis undergoing gastro-endoscopy. Genomic DNA was extracted from the samples. Silver staining single strand conformation polymorphis-polymerize chain reaction (SSCP-PCR) was used to screen MSI markers at 5 loci (Bat-25, Bat-26, D5S346, D17S250, and D2S123) in fresh tissues and formalin-fixed, paraffin-embedded samples and their corresponding normal gastric mucosa.

RESULTS: The abnormal shifting of the single-strand DNA (MSI) was identified in 21 out of 36 (58.3%) gastric cancers. Seven cases showed high-level MSI (two or more loci altered) and 14 showed low-level MSI (one locus altered). Gastric cancer with MSI had a tendency to be located in the distal stomach. MSI was also detected in 11 out of 41 (26.8%) dysplasia samples and in 9 of 51 (17.6%) IM samples respectively. Three cases of dysplasia and one case of IM showed high-level MSI. Eight cases of dysplasia and 8 cases of IM displayed low-level MSI. MIS in IM was found only in moderate or severe-grade IM. No association was detected between MSI and dysplasia grade.

CONCLUSION: Accumulation of MSI in dysplasia and intestinal metaplasia of gastric mucosa may be an early molecular event during gastric carcinogenesis and may contribute to the acquisition of transformed cell phenotype and the development of gastric cancer.