Microsatellite instability in precancerous lesions and adenocarcinomas of the stomach

AKT plays a crucial role in gastric cancer

The AKT protein is involved in the phosphatidylinositol-3 kinase signaling pathway and is a vital regulator of survival, proliferation and differentiation in various types of cells. Helicobacter pylori infection induces epithelial cell proliferation and oxidative stress in chronic gastritis. These alterations lead to telomere shortening, resulting in the activation of telomerase. AKT, in particular, is activated by H. pylori-induced inflammation. AKT then promotes the expression of human telomerase reverse transcriptase, which encodes a catalytic subunit of telomerase, and induces telomerase activity, an essential component of the process of carcinogenesis. AKT activation is increased in gastric mucosa with carcinogenic properties and is associated with the low survival of patients with gastric cancer. The findings of the present study suggest that AKT is pivotal in gastric carcinogenesis and progression.

Introduction of an examination and treatment for Helicobacter pylori infection in high school health screening

BACKGROUND

Recently, a significant relationship between gastric cancer and Helicobacter pylori infection has been proven. The purpose of this study was to elucidate the actual conditions of H. pylori infection in Japanese teenagers.

METHODS

The study subjects were students at a certain high school between 2007 and 2009. They were first examined with a urinary rapid test kit based on immunochromatographic technology [corrected] for detection of the antibody to H. pylori (RAPIRAN®). [corrected]. Students who tested positive on this screening examination visited Shinshu University Hospital and received esophagogastroduodenoscopy, and biopsy samples were taken to examine their H. pylori status. The resolution of H. pylori infection was assessed by urea breath test.

RESULTS

For 3 years, 1,224 of 1,232 students (99.4%) received a screening examination for H. pylori infection. Sixty-four of these 1,224 students (5.2%) were found to be positive for H. pylori. Thirty of these 64 H. pylori-positive students visited our hospital, and 24 of them (80%) were confirmed to be infected by H. pylori. The most common endoscopic findings for students with H. pylori infection were nodular gastritis (58.3%) and closed-type atrophic gastritis (45.8%). Histological findings showed no evidence of intestinal metaplasia, except in one of the students. All 24 students were successfully cured of H. pylori infection. If this procedure were to be introduced into the nationwide health screening at Japanese high schools, we calculated that the cost of the prevention of a gastric cancer would be 454,073 yen for each person.

CONCLUSIONS

The low rate of prevalence of H. pylori infection in Japanese teenagers would make it possible to perform examinations and carry out treatment for this infection in high school health screenings from the standpoint of medical economy.

Premalignant lesions in gastric cancer

Despite a plateau in incidence, gastric cancer is one of the most common cancers worldwide and causes considerable morbidity and mortality. Premalignant gastric lesions are well known risk factors for the development of intestinal-type gastric adenocarcinomas. In this multistep model of gastric carcinogenesis, Helicobacter pylori causes chronic active inflammation of the gastric mucosa, which slowly progresses through the premalignant stages of atrophic gastritis, intestinal metaplasia, and adenoma/dysplasia to gastric carcinoma. This progression is paralleled by a stepwise accumulation of multiple genetic and epigenetic abnormalities. Detection, treatment, and molecular analyses of premalignant lesions may thus provide a basis for gastric cancer prevention. This review describes an overview of current knowledge on premalignant gastric lesions. It also reviews the issue of surveillance of patients with premalignant lesions in order to improve the survival of patients with gastric cancer.

Clinicopathologic and immunohistochemistry characterization of synchronous multiple primary gastric adenocarcinoma

The aim of this investigation was to evaluate clinicopathologic and immunohistochemical characteristics of synchronous primary gastric adenocarcinomas. Immunohistochemistry for p53 (suppressor pathway) and for hMLH1, hMSH2, and hMSH6 (mutator pathway) was performed using ABC-technique amplification by biotinylated tyramide. Synchronous primary gastric adenocarcinomas were detected in 19/553 (3.43%) of the patients. The tumors were localized in distal stomach in 22, body in 14, and proximal in five. There was a predominance of intestinal type in the group of synchronic tumors compared to the solitary lesions, 73.2 vs 37.3%, p = 0.001. Synchronous neoplasias were diagnosed in earlier stage than solitary neoplasias, T1-T2 = 60.9% vs T1-T2 = 28.4%, p = 0.0001; and N0 = 68.4% vs N0 = 26.2%, p = 0.001. p53 was detected in 52.6% of the patients with synchronous tumors. Altered hMLH1 immunoexpression occurred in 26.3% of the patients and hMSH6 in 5.3%. hMSH2 immunoreactivity was positive in all tumors. p53 was solely detected in 17 tumors, while hMLH1 was altered in 10/24 negative p53 tumors, p = 0.01. Synchronous gastric adenocarcinomas presented higher frequency of intestinal type and early gastric cancer in comparison to solitary gastric cancer. Two routes of carcinogenesis, mutator, and suppressor appear to be involved independently in the development of synchronous tumors.

Assessment of microsatellite instability status for the prediction of metachronous recurrence after initial endoscopic submucosal dissection for early gastric cancer

The technique of endoscopic submucosal dissection (ESD) has been developed for en bloc resection of early gastric cancer (EGC); however, little is known about the risk of metachronous cancer in the remnant stomach after initial ESD. In this study, we investigated the correlation between microsatellite instability (MSI) status and the incidence of metachronous recurrence of gastric cancer. According to the genetic/molecular background determined with MSI status and expression levels of hMLH1 and p53 tumour suppressor, 110 EGCs removed with ESD were subclassified into three groups: the mutator/MSI-type (8%), suppressor/p53-type (45%) and unclassified type (47%). Interestingly, patients with the mutator/MSI-type tumour had a high incidence (67%) of metachronous recurrence of gastric cancer within a 3-year observation after initial ESD, which was significantly higher than those with the suppressor/p53-type and unclassified type tumours (P<0.01). Although we investigated mucin phenotypes, there was no correlation between mucin phenotype and the recurrence of EGC. These findings suggest that subclassification of molecular pathological pathways in EGCs is required for the assessment of patients with a high risk of recurrent gastric cancer. The information delivered from our investigation is expected to be of value for decisions about therapy and surveillance after ESD.

Microsatellite instability and gastric non-invasive neoplasia in a high risk population in Cesena, Italy

BACKGROUND/AIMS

In the natural history of gastric cancer, non-invasive neoplasia (NiN) precedes invasive carcinoma. A histological classification of gastric NiN has recently been proposed by a World Health Organisation international panel of experts. Genetic instability is known to be among the molecular pathways involved in gastric oncogenesis. In this retrospective cross sectional study, microsatellite instability (MSI) was analysed in a consecutive series of NiN and NiN related histological alterations from a northern Italian region at high risk for gastric cancer.

PATIENTS/METHODS

Fifty five consecutive cases (indefinite for NiN, 29 cases; low grade NiN, 17 cases; high grade NiN, nine cases) were analysed by radioactive polymerase chain reaction and electrophoresis for microsatellite alterations at six loci (BAT25, BAT26, D2S123, D5S346, D17S250, and D3S1317). MSI was defined according to the Bethesda criteria distinguishing: (1) no instability in the analysed loci; (2) low frequency MSI (MSI-L); and (3) high frequency MSI (MSI-H). Immunohistochemical expression of MLH1 and MSH2 proteins was also analysed in all cases.

RESULTS

Overall, MSI was found in 11 of 55 cases (indefinite for NiN, five of 29 (MSI-L, four; MSI-H, one); low grade NiN, three of 17 (MSI-L, one; MSI-H, two); high grade NiN, three of nine (MSI-L, one; MSI-H, two).

CONCLUSIONS

In an Italian high risk area for gastric cancer, MSI is part of the spectrum of genetic alterations in gastric non-invasive neoplasia. In European populations at high risk of gastric cancer, DNA repair system alterations are thought to be among the early molecular events in gastric carcinogenesis.

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.

High frequency of microsatellite instability in intestinal-type gastric cancer in Korean patients

BACKGROUND

Although there have been some reports on microsatellite alterations in gastric cancer, findings are inconsistent regarding the associations between histological classification and microsatellite instability (MSI). In the present study, we attempted to determine whether Lauren's histological subtypes are related with MSI status.

METHODS

Paraffin-embedded tissue samples from 14 diffuse-type and 14 intestinal-type gastric adenocarcinomas were matched up according to patient gender and age. Mononucleotide markers (BAT25 and BAT26) and dinucleotide markers (D2S123, D5S346, and D175S250) were used for MSI analyses. Microsatellite genotypes were categorized in terms of high MSI incidence (MSI-H, >30% positive marker) or low MSI incidence (MSI-L, <30% positive marker). Losses of hMLH1 and hMSH2 protein expression were immunohistochemically studied.

RESULTS

MSI-H was observed in 11 cases (78%) of the 14 intestinal-type cases as compared to 3 (21%) of the 14 diffuse-type cases (p=0.007). In MSI-H tumors, 10 cases (71%) showed losses of hMLH1 protein expression, while 2 cases (14%) in MSI-L tumors showed losses of hMLH1 protein expression (p=0.006).

CONCLUSION

MSI-H tumors are more frequently found in intestinal-type gastric cancer, which suggests the possibility that there are different pathogenic pathways in gastric carcinogenesis according to histologic type.

Geno- and pheno-typic characterization in ten patients with double-primary gastric and colorectal adenocarcinomas

BACKGROUND AND AIMS

Although a number of double-primary gastric and colorectal cancers have been known to correlate with the mutator pathway, a possible association with known hereditary cancers regarding geno-pathogenesis has rarely been investigated. This study was intended to identify a possible association of hereditary cancers and the implications of the mutator or tumor-suppressor pathway in double-primary gastric and colorectal cancers.

MATERIALS AND METHODS

Fresh colorectal tissues and lymphocytes from ten patients with double-primary gastric and colorectal cancers were obtained consecutively. The mutator pathway was evaluated by detecting hMSH2 and hMLH1 mutations, microsatellite instability (MSI) using 12 microsatellite markers, and hMLH1 promoter region methylation. Protein expressions of hMSH2, hMLH1, APC, E-cadherin, and beta-catenin were identified by immune staining.

RESULTS

There was no pathogenic mutation in any introns or exons of hMSH2, hMLH1 or CDH1, and in exons 3, 5, 6, and 15 of CTNNB1. Either MSI or methylator phenotype was found in five gastric cancers and in four colorectal cancers. No patients met the Amsterdam criteria of hereditary nonpolyposis colorectal cancer (HNPCC) or its equivalent of hereditary gastric cancer. Two patients with gastric cancers among their first-degree relatives showed no E-cadherin expression. The two of the three patients with rectal cancers among their first-degree relatives showed mutator phenotype either in the gastric or in the colorectal cancer. A subset of double-primary gastric and colorectal cancers may thereby be categorized as variant forms of hereditary gastric or colorectal cancer. Both cytoplasmic and nuclear beta-catenins were expressed in all gastric and colorectal cancers. Among the gastric and colorectal cancers with either MSI or methylator phenotype, four of five gastric cancers showed both APC and E-cadherin expression, whereas one of four colorectal cancers showed them.

CONCLUSION

This may suggest that the mutator pathway and the aberrant tumor suppressor pathway of the APC-E-cadherin may be cooperative or separately activated in the geno-pathogenesis of double-primary gastric and colorectal cancers.

P53 and Rb tumor suppressor gene alterations in gastric cancer

Inactivation of tumor suppressor genes has been frequently observed in gastric carcinogenesis. Our purpose was to study the involvement of p53, APC, DCC, and Rb genes in gastric carcinoma.

METHOD

Loss of heterozygosity of the p53, APC, DCC and Rb genes was studied in 22 gastric cancer tissues using polymerase chain reaction; single-strand conformation polymorphism of the p53 gene exons 5-6 and exons 7-8 was studied using 35S-dATP, and p53 expression was detected using a histological immunoperoxidase method with an anti-p53 clone.

RESULTS AND DISCUSSION

No loss of heterozygosity was observed in any of these tumor suppressor genes; homozygous deletion was detected in the Rb gene in 23% (3/13) of the cases of intestinal-type gastric carcinoma. Eighteen (81.8%) cases showed band mobility shifts in exons 5-6 and/or 7-8 of the p53 gene. The presence of the p53 protein was positive in gastric cancer cells in 14 cases (63.6%). Normal gastric mucosa showed negative staining for p53; thus, the immunoreactivity was likely to represent mutant forms. The correlation of band mobility shift and the immunoreactivity to anti-p53 was not significant (P =.90). There was no correlation of gene alterations with the disease severity.

CONCLUSIONS

The inactivation of Rb and p53 genes is involved in gastric carcinogenesis in our environment. Loss of the Rb gene observed only in the intestinal-type gastric cancer should be further evaluated in association with Helicobacter pylori infection. The p53 gene was affected in both intestinal and diffuse histological types of gastric cancer.

Alterations of DNA mismatch repair proteins and microsatellite instability levels in gastric cancer cell lines

Alterations in DNA mismatch repair (MMR) proteins result in microsatellite instability (MSI), increased mutation accumulation at target genes and cancer development. About one-third of gastric cancers display high-level microsatellite instability (MSI-High) and low-level microsatellite instability (MSI-Low) is frequently detected. To determine whether variations in the levels of MMR proteins or mutations in the main DNA MMR genes are associated with MSI-Low and MSI-High in gastric cancer cell lines, the MSI status (MSI-High, MSI-Low or MS-Stable (MSS)) of 14 gastric cancer lines was determined using multiple clone analysis with a panel of five microsatellite markers. Protein levels of hMLH1, hMSH2, hMSH6, hPMS2 and hPMS1 were determined by Western blot. Sequence analysis of hMLH1 and hMSH2 was performed and the methylation status of the hMLH1 promoter was examined. The cell lines SNU1 and SNU638 showed MSI-High, decreased to essentially absent hMLH1 and hPMS2 and reduced hPMS1 and hMSH6 protein levels. The hMLH1 promoter region was hypermethylated in SNU638 cells. The MKN28, MKN87, KATOIII and SNU601 cell lines showed MSI-Low. The MMR protein levels of cells with MSI-Low status was similar to the levels detected in MSS cells. A marked decrease in the expression levels of MutL MMR proteins (hMLH1, hPMS2 and hPMS1) is associated with high levels of MSI mutations in gastric cancer cells. Gastric cancer cell lines with MSI-Low status do not show significant changes in the levels of the main DNA MMR proteins or mutations in the DNA mismatch repair genes hMSH2 and hMLH1. These well-characterized gastric cancer cell lines are a valuable resource to further our understanding of DNA MMR deficiency in cancer development, progression and prognosis.

Carbonic anhydrase isozymes IX and XII in gastric tumors

AIM: To systematically study the expression of carbonic anhydrase (CA) isozymes IX and XII in gastric tumors.

METHODS: We analyzed a representative series of specimens from non-neoplastic gastric mucosa and from various dysplastic and neoplastic gastric lesions for the expression of CA IX and XII. Immunohistochemical staining was performed using isozyme-specific antibodies and biotin-streptavidin complex method.

RESULTS: CA IX was highly expressed in the normal gastric mucosa and remained positive in many gastric tumors. In adenomas, CA IX expression significantly decreased towards the high grade dysplasia. However, the expression resumed back to the normal level in well differentiated adenocarcinomas, while it again declined in carcinomas with less differentiation. In comparison, CA XII showed no or weak immunoreaction in the normal gastric mucosa and was slightly increased in tumors.

CONCLUSION: These results demonstrate that CA IX expression is sustained in several types of gastric tumors. The variations observed in the CA IX levels support the concept that gastric adenomas and carcinomas are distinct entities and do not represent progressive steps of a single pathway.

Helicobacter pylori impairs DNA mismatch repair in gastric epithelial cells

BACKGROUND & AIMS

Helicobacter pylori infection is a major gastric cancer risk factor. H. pylori gastritis occurs more frequently in individuals with microsatellite instability-positive than those with microsatellite instability-negative gastric cancers, raising the possibility that H. pylori infection affects DNA mismatch repair (MMR). The aim of this study was to determine the effect of H. pylori on the expression of DNA MMR proteins and RNA in gastric epithelial cells.

METHODS

Gastric cancer cell lines were cocultured with H. pylori, bacterial extracts, and Campylobacter jejuni or Escherichia coli. MutS (hMSH2 and hMSH6) and MutL (hMLH1, hPMS2, and hPMS1) DNA MMR protein and RNA levels were determined.

RESULTS

All cell lines examined showed decreased levels of MutS and MutL DNA MMR proteins in a dose-dependent manner after coculture with H. pylori strains. The reduction in DNA MMR protein levels was caused by heat-sensitive H. pylori products. The levels of DNA MMR proteins were affected by C. jejuni but not by E. coli. RNA levels of hMSH2 and hMSH6 were also reduced after exposure to H. pylori.

CONCLUSIONS

H. pylori infection of gastric epithelial cells leads to a decrease in DNA MMR proteins that is at least in part related to an H. pylori-induced decrease in messenger RNA levels of repair genes. These data suggest that H. pylori infection might lead to a deficiency of DNA MMR in gastric epithelial cells that may increase the risk of mutation accumulation in gastric mucosa cells and the risk of gastric cancer during chronic H. pylori infection.

Field population-based blocking treatment of esophageal epithelia dysplasia

AIM

To confirm the value of blocking treatment by zenshengping (ZSP), a Chinese herb composite, and Riboflavin for esophageal epithelia dysplasia cases screened out in high risk area in northern china by exfoliative balloon cytology (EBC), so to reduce the incidence rate of esophageal cancer(EC).

METHODS

Esophageal epithelium dysplasia cases including mind esophageal epithelium dysplasia (MEED), stage one severe esophageal epithelium dysplasia (SEED I), and stage two severe esophageal epithelium dysplasia (SEED II) were screened out from people aged 40 years and older in the high risk area of Chixian. These cases were randomly divided into a treatment and control group. Subjects in the treatment and control groups took ZSP, riboflavin, and placebo daily for three years. EC cases registered by cancer registry and identified by EBC re-screening in the treatment and control groups were used to calculate incidence and blocking rates to demonstrate the effects of blocking medication.

RESULTS

It was found that 31.92% and 24.15% of people aged 40 years and older in Cixian could been diagnosed as MEED and SEED cases. The severity of dysplasia increased with age. ZSP had blocked EC occurrence by 47.79% after 3 year medication among the SEED cases.

CONCLUSION

ZSP can block the development from SEED I and SEED II to EC by 47.79%. Efforts should be made to screen and treat dysplasia cases in people aged 40 years and older in high risk areas to reduce the mortality figures.

Gene mutation as a target for early detection in cancer diagnosis

The increasing number of genetic aberrations implicated in the development of human cancer has prompted a search to detect them at the earliest possible stage of their formation. Of the many such genetic changes identified thus far, relatively few meet the standard for markers in early diagnosis and prognosis, namely that the genetic modifications occur during the early onset phase of cancer development. Parallel to the increasing number of such genes is the growing availability of technologies using more powerful and cost-efficient methods that enable mass screening for genetic alterations. The purpose of this review is to summarize the currently available genes that can serve as markers for early detection of cancers and methods that allow their detection.

Expression of hMLH1 is inactivated in the gastric adenomas with enhanced microsatellite instability

Microsatellite instability (MSI) and frameshift mutations in the genes containing coding nucleotide repeats have been reported in a subset of gastric adenomas, however the inactivation profiles of DNA mismatch repair genes in MSI-positive gastric adenomas have not been characterized. To address the origin of MSI in gastric adenomas, expressions of hMLH1 and hMSH2 were explored in 86 gastric adenomas. Gastric carcinomas, of which 16 were MSI-positive and 22 MSI-negative, were used as controls. MSI was found in 15 (17%) of gastric adenomas. Absent or decreased hMLH1 expression by immunohistochemistry was noted in most of the MSI-positive adenomas (13/15, 87%) and carcinomas (14/16, 88%), and all of these tumours showed methylation of the hMLH1 gene promoter. In contrast, rare inactivation of hMLH1 expression was found in MSI-negative adenomas (3/71, 4%) and carcinomas (2/22, 9%). Intense expression of hMSH2 gene product was observed in most of the gastric adenomas and carcinomas regardless of MSI status. These findings indicate that the inactivation of hMLH1 gene expression by promoter methylation is an early event and might be the origin of MSI-positive gastric adenomas.

Microsatellite instability in inflamed and neoplastic epithelium in ulcerative colitis

BACKGROUND

Several genetic alterations have been documented in dysplasia and cancer developing in ulcerative colitis (UC). However, the microsatellite instability (MSI) status has rarely been described, especially in the inflamed epithelium of UC.

AIMS

To study MSI status during neoplastic and inflammatory changes in UC.

METHODS

Seventy five surgically resected samples of colorectal mucosa, taken from 16 colectomy specimens of patients with UC were examined: five patients had a long duration with dysplasia or cancer (UC-LD with neoplasm), seven patients had a long duration without neoplastic changes (UC-LD without neoplasm), and four patients had a short duration without neoplastic changes (UC-SD). In addition to MSI status examined by six microsatellite markers, p53 expression was compared among the three groups.

RESULTS

With regard to non-neoplastic inflamed epithelium, MSI in two or more loci (MSI> or =2) was seen more frequently in the UC-LD without neoplasm group than in the UC-SD group (six of 14 v one of 12; p = 0.060), and significantly more often than in the UC-LD with neoplasm group (six of 14 v two of 23; p = 0.016). In the UC-LD without neoplasm group, MSI> or =2 was detected significantly more frequently in patients with severe inflammation than in those with mild inflammation (six of nine v none of five; p = 0.028). With regard to neoplastic epithelium in the UC-LD with neoplasm group, MSI in two or more loci was found in three of 17, and p53 overexpression was seen in 11 of 17 of the neoplastic lesions.

CONCLUSIONS

A high incidence of MSI in long standing UC with severe inflammation probably reflects genomic instability caused by repeated inflammatory stress. Thus, the influence of inflammation should be considered when estimating MSI in UC. It is possible that changes in p53 expression are important in the development of cancer in UC.

Molecular testing of Helicobacter pylori-associated chronic gastritis and premalignant gastric lesions: clinical implications

Helicobacter pylori-associated gastritis may progress or be complicated by peptic ulcer and gastric malignancy, including gastric carcinoma and mucosa-associated lymphoid tissue lymphoma. Predicting who develops malignancy remains a clinical challenge. The molecular understanding of pathways that are associated with progression of the normal gastric epithelium to malignancy together with classic histologic parameters are promising ways of tackling this problem. Ideally, molecular tools used for screening should be available as noninvasive tests, such as examination of markers detectable in blood samples, but these are not currently available. In contrast, molecular markers that correlate with cancer risk can be examined in the epithelium after endoscopic biopsy and can be of importance in identifying individuals at risk, especially if combined with other parameters of gastric cancer risk.

Clinical significance of mutator phenotype and chromosome 17p and 18q allelic loss in gastric cancer

BACKGROUND

Tumour stage is the only reliable prognostic factor for gastric cancer. The molecular anomalies involved in this process have the potential to serve as additional prognostic markers.

METHODS

Forty-four gastric cancers, treated by surgery alone, have been analysed for chromosome 17p and 18q allelic loss and for the presence of microsatellite instability (MSI), using microsatellite markers and DNA from paraffin-embedded tumours.

RESULTS

Eight cancers showed a MSI-positive (MSI+) phenotype. Among the 36 MSI-negative cancers, chromosome 17p and 18q allelic losses were found in 22 of 34 and 19 of 33 informative cases respectively. Multivariate survival analysis indicated MSI status to be an independent prognostic factor along with the tumour stage. MSI+ cancers were associated with longer patient survival, whereas MSI-negative cancers had a significantly poorer prognosis (P = 0.007), with a median actuarial survival of 24 months.

CONCLUSION

MSI status is an independent prognostic factor among gastric cancers at the same stage. Chromosome 17p and 18q status added no additional prognostic information to that of tumour stage. The combined use of tumour stage and MSI status may help in deciding whether patients with advanced gastric cancer require additional therapy other than surgery alone.

Chromosomal alterations in paired gastric adenomas and carcinomas

Gastric adenoma is a precancerous lesion of the stomach and its malignant transformation is thought to result from accumulative series of gene alterations. The aim of this study was to determine the pattern of chromosomal changes during gastric carcinogenesis. Pairs of adenoma and carcinoma tissues from 15 gastrectomy cases containing both adenomas and carcinomas in the same (adjacent pairs, 6 cases) and different (non-adjacent pairs, 9 cases) lesions, were analyzed for chromosomal alterations of 39 non-acrocentric chromosomal arms by comparative genomic hybridization (CGH). CGH analysis identified frequent chromosomal alterations in most of the gastric adenomas (14/15, 93%) and all of the carcinomas. The mean number of chromosomal alterations was higher in carcinoma (5.5 for adenoma and 11.7 for carcinoma; P = 0.006, by nonparametric Wilcoxon's test). Losses on the short arm of chromosome 17 were most common in both adenomas (43%) and carcinomas (67%). The pattern of chromosomal alterations in paired gastric adenomas and carcinomas showed greater similarity compared to the non-case pairs and this similarity was increased in the adjacent pairs. Deletion mapping analysis on chromosome 17p also demonstrated that the conserved deletion area was more frequent in the adjacent pairs. Among these 6 adjacent pairs, all had common deletion areas. In contrast, among the 9 non-adjacent pairs, 2 (22%) had common area of deletion, 5 (56%) showed deletion only in the carcinoma, and the remaining 2 (22%) had no deletion on 17p, suggesting diverse genetic changes might be involved in the multiple tumor formation. Our results that common clonal genetic changes between adjacent pairs of gastric adenomas and carcinomas and accumulated genetic changes in the carcinomas provide evidences for the stepwise mode of gastric carcinogenesis through the accumulation of a series of genetic alterations.

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

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

Clinical usefulness of microsatellite instability for the prediction of gastric adenoma or adenocarcinoma in patients with chronic gastritis

To assess a role of microsatellite instability (MSI) in the development of gastric adenocarcinoma or adenoma from chronic gastritis, we analysed mutations of five microsatellite loci in gastritis, adenoma and adenocarcinoma retrospectively. Gastric mucosa was biopsied from the same area in each patient at different periods and examined for MSI. Only one of 55 patients with chronic gastritis revealed MSI-H phenotype and the other 54 patients showed microsatellite stable (MSS) phenotypes. In six of 17 patients with gastric adenoma or well-differentiated adenocarcinoma, MSI-positive phenotypes were demonstrated. Interestingly, all of six patients showing MSI, including three high-level MSI (MSI-H) cases and three low-level (MSH-L) cases, had already revealed MSI at the stage of chronic gastritis. In two of three MSI-H cases, the identical MSI patterns had been observed at the stage of gastritis 1.5-7 years before the final diagnosis of adenocarcinoma. The adjacent gastritis mucosa within 10 mm from the carcinoma demonstrated MSI as well. MSI was not found in any of 35 patients with Helicobacter pylori infection, but found in one of 30 patients without infection. Moreover, two of three cases of gastric adenoma or well-differentiated adenocarcinoma with MSI-H at the stage of chronic gastritis showed no evidence of Helicobacter pylori infection throughout the observation periods. These results indicate that MSI in biopsy specimens at the stage of chronic gastritis may predict the risk of the progression to adenoma and well-differentiated adenocarcinoma, and that Helicobacter pylori infection itself may not induce MSI directly in the gastric mucosa.

Microsatellite instability in gastric intestinal metaplasia in patients with and without gastric cancer

The role and significance of microsatellite instability (MSI) in gastric carcinogenesis remain unknown. This study determined the chronology of MSI in gastric carcinogenesis by examining intestinal metaplasia (IM) from patients with and without gastric cancer. DNA was obtained from gastric specimens of 75 patients with gastric IM (30 cancer, 26 peptic ulcer, and 19 chronic gastritis patients) and was amplified with a set of eight microsatellite markers. Eight (26. 7%) tumors and seven (9.3%) IM samples (three from cancer-free patients) displayed high-level MSI (three or more loci altered). Low-level MSI (one or two loci altered) was detected in 50% of the tumors, in 40% of IM samples coexisting with cancer, and in 38% of IM tissues of cancer-free individuals. Among the 30 cancer patients, microsatellites were more frequently altered in IM coexisting with tumors that showed MSI (P = 0.003). In addition, patients with low-level MSI in the tumor tissues were more likely to have active Helicobacter pylori infection than those with stable tumors (P = 0.02). In conclusion, this study indicates that MSI occurs not only in gastric IM of patients with gastric carcinoma, but also in IM of cancer-free individuals. These data suggest that the progressive accumulation of MSI in areas of IM may contribute to gastric cancer development, representing an important molecular event in the multistep gastric carcinogenesis cascade.

Microsatellite instability in the adenoma-carcinoma sequence of the stomach

Sixty-three cases of stomach resections harboring both adenoma and carcinoma were analyzed for microsatellite instability (MSI). The cases included 28 carcinomas arising from adenoma (Type I) and 35 carcinomas with separate adenoma (Type II). The results of MSI assessed by 49 markers were the same for BAT-26 instability. The incidence of MSI was 21% in gastric adenoma and 30% in gastric carcinoma, which is significantly higher than gastric carcinoma without associated adenoma (p < 0.01). Five of eight (63%) cases of multiple carcinomas associated with adenoma showed MSI+ in adenoma and in one or more carcinoma lesion(s). Eight of thirteen (62%) MSI+ adenomas were associated with carcinoma, whereas 20 of 50 (40%) MSI adenomas were associated with carcinoma. MSI+ adenomas of Type I showed a higher mutation rate of the TGF-beta RII gene than Type II (88% versus 40%). Gastric adenoma with TGF-beta RII gene mutation was more prone to transform into carcinoma (p = 0.03). This study revealed that gastric carcinoma arising from adenoma is frequently associated with a mismatch repair deficiency mechanism. In the gastric adenoma-carcinoma sequence, TGF-beta RII gene mutation occurred early in the adenoma stage and it persisted after malignant transformation.

Consilience across evolving dysplasias affecting myeloid, cervical, esophageal, gastric and liver cells: common themes and emerging patterns

In the present paper, an attempt is made to identify common biologic themes across dysplastic states affecting the marrow, gastro intestinal tissue, the cervix and liver as well as unifying patterns during disease evolution. The following algorithm appears generally applicable, although individual variations must necessarily be anticipated. It appears that there is an initial transforming event which in all dysplasias except that affecting the marrow has been found to be infectious. Increased cellular proliferation-increased apoptosis, telomere shortening, appearance of telomerase expression and clonal expansion follow the initial insult. Abnormalities in the cytokine environment are universally described and it is likely that the quintessential monoclonality aspect of dysplasia predisposes to accumulation of genetic mutations, and microsatellite instability leading to the appearance of evolved sub-clones. The conversion of a dysplastic phenotype to a malignant one reflects the success of one such sub-clone in developing a survival advantage over a large population of prematurely apoptotic neighbors. This state is usually acquired by silencing tumor suppressor genes through hypermethylation or actual loss or dysfunction. Thus, excessive apoptosis of cells resulting from a persistent infectious process predisposes the organ towards developing a cancerous phenotype. Evidence for the shared pathology is presented at length with the hope that these parallels between dysplastic states will be helpful in both biologic and therapeutic research.

Gross type-matched study of clinicopathologic features of advanced gastric carcinoma with replication error

Sporadic gastric carcinomas with replication error (RER) have been described and have distinct clinicopathological features, such as: older age group, predominant antral location, elevated gross type, near-diploidy, expanding pattern (Ming's classification), intestinal type, low desmoplastic response, and less frequent lymph node metastasis. Previous study revealed that replication error-positive (RER+) advanced gastric carcinomas (AGC) had a preponderance of Borrmann type 2. Regardless of RER status, AGC of Borrmann type 2 usually exhibit expanding pattern (Ming's classification), intestinal type, and low desmoplastic reaction. Therefore, to better characterize the clinicopathological features of RER+ gastric carcinomas, gross type-matched analysis would be necessary. We analyzed 53 cases of Borrmann type 2 AGC for RER status using polymerase chain reaction analysis of eight microsatellite loci and compared the clinicopathological features between RER+ and RER-negative (RER-) tumors. Sixteen (30.2%) out of 53 cases were RER+ phenotype which had a significant association with female sex, older age, expanding pattern, small and uniform nuclei, and low DNA index (P < 0.05). However, RER status was not significantly associated with histological differentiation, histological type (Lauren's classification), desmoplastic response, intratumoral lymphoid infiltration, and tumor location. Most of the previously known clinicopathological features of RER+ AGC were related to Borrmann type 2, except for female sex, older age, expanding pattern, and low DNA index.

Molecular biology of gastric carcinoma: from laboratory to bedside

Although the advancement of molecular oncology in gastric cancer lags behind that of colorectal cancer, the rapid developments witnessed in recent years have improved our understanding of the carcinogenesis, aetiology, progression and metastasis of gastric cancer. The different molecular genetic alterations in intestinal and diffuse types of gastric cancer have further supported the concept that these two pathological types are different disease entities. The association of telomerase and cadherin changes with Helicobacter pylori infection reinforces its aetiological role. The mutated cadherin gene identified in familial gastric cancer has shone light onto the pathogenesis. Adhesion molecules have already been applied to daily clinical practice as prognostic markers. Future molecular studies will contribute to the screening, classification, disease monitoring and therapeutics of gastric cancer.

Infrequent loss of heterozygosity of APC/MCC and DCC genes in gastric cancer showing DNA microsatellite instability

AIM

To investigate the role of DNA microsatellite instability (MSI) in gastric carcinogenesis by studying associations between MSI status, clinicopathological features, and loss of genetic loci.

METHODS

Six microsatellite loci and loss of heterozygosity at APC, DCC, and MCC were analysed by polymerase chain reaction based methods in 53 cases of advanced gastric cancer.

RESULTS

MSI was observed in 32.1% of gastric carcinomas (17/53) and 20% of foci of intestinal metaplasia (3/15). Seven gastric carcinomas (13.7%) were MSI-high (MSI-H) (three loci or more) and 10 (18.9%) were MSI-low (MSI-L) (one or two loci). The frequency of MSI-H was higher in intestinal (25.0%) than in diffuse carcinomas (3.7%) (p < 0.05). None of the MSI-H tumours showed loss of heterozygosity at APC, MCC, or DCC loci.

CONCLUSIONS

MSI may have an important and early role in a subset of gastric cancers, particularly the intestinal type. The MSI-H subset of gastric cancer has features in common with its colorectal counterpart, whereas MSI-L and microsatellite stable cancers appear to develop through the loss of heterozygosity pathway.

Microsatellite instability and K-ras mutations in gastric adenomas, with reference to associated gastric cancers

Gastric adenomas are often detected in the stomach resected for gastric cancer. Previous investigation have revealed that the prevalence of their malignant transformation is generally low, but the frequent coexistence with carcinoma suggests that they may share some common processes with gastric cancer in tumorigenesis. In contrast to the cumulative information about genetic alterations in gastric cancer, inquiries into the genetic changes of adenoma and coexisting carcinoma in the same individual's stomach are still few. We investigated microsatellite instability (MSI) and K-ras point mutations in codons 12 and 13 in 50 lesions of gastric adenomas in 43 cases, and 31 lesions of gastric cancers that coexisted with these adenomas. In gastric adenomas, we found seven lesions (14.0%) to have microsatellite instability (MSI) at one or more loci, and most of them (six cases) had MSI at only one locus and were not associated with alterations in presumable target molecules. MSI was detected more frequently (11/31, 35.5%) and more extensively (five lesions at multiple loci) in accompanying gastric carcinomas. The prevalence of MSI in adenomas was more frequently found in those with synchronous gastric cancer (6/37, 16.2%, vs. 1/13, 7.6%) than without, and gastric adenoma accompanied by gastric cancer with multiple MSI tended to have MSI more frequently than that accompanied by cancer without MSI (4/5, 80%, vs. 1/24, 4.2%; p = 0. 01). In at least some individuals, MSI appears to represent one step in the pathway of gastric tumorigenesis, shared by adenoma and carcinoma. We found K-ras gene alteration in 8 lesions (16.0%) out of 50 gastric flat adenomas and no difference in its prevalence between adenoma with or without cancer. Only one gastric cancer, which had adenoma without K-ras mutation, had K-ras codon 12 mutation. Adenomas with a higher grade of atypia (p < 0.05) more frequently carried K-ras point mutation, which is consistent with the situation in colorectal adenoma. We conclude that MSI, not K-ras mutation, is a shared genetic alteration in adenoma and carcinoma of the individual stomach.

In situ mRNA hybridization technique for analysis of human telomerase RNA in gastric precancerous and cancerous lesions

Telomerase, the ribonucleoprotein enzyme that elongates telomerase, is repressed in normal somatic cells but is reactivated during tumor progression. The purpose of this study was to investigate the localization of human telomerase RNA (hTR) expression in human gastric precancerous and cancerous lesions by using in situ mRNA hybridization (ISH) with avidin-biotin staining. We also examined telomerase activity in these lesions by using hybridization protection assay connected with a telomeric repeat amplification protocol (TRAP/HPA). Analyzed tissue samples were as follows; 132 cases of chronic atrophic gastritis without intestinal metaplasia, 115 incomplete-type intestinal metaplasias, 40 complete-type intestinal metaplasias, 23 hyperplastic polyps, 23 tubular adenomas and 26 adenocarcinomas. In ISH analysis, high levels of hTR expression were observed preferentially in the nuclei at the single-cell level. hTR-expressing cells in carcinomas and adenomas were significantly more frequent than those of the other lesions (P < 0.001). The expression pattern of hTR in carcinoma and adenoma tissues was heterogeneous and similar intratumor heterogeneity was detected in Ki-67 immunoreactivity. Infiltrating lymphocytes in tissue also exhibited high levels of hTR expression. In TRAP/HPA analysis, carcinomas had significantly more frequent positivity for telomerase activity and a higher level of telomerase activity than the other lesions (P < 0.05). However, the amount of telomerase activity did not parallel the expression level of hTR. Our data suggest that hTR expression increases in the early stages of stomach carcinogenesis and that sufficient synthesis of hTR is a prerequisite for telomerase reactivation in tumorigenesis.

Altered microsatellites in incomplete-type intestinal metaplasia adjacent to primary gastric cancers

AIM

To investigate the presence of genetic instability in precancerous lesions of the stomach.

METHODS

Fifteen cases of sporadic gastric cancers with a background of intestinal metaplasia were studied by microsatellite assay at nine loci. Altered metaplastic mucosa was microdissected, reconstructed topographically, and examined immunohistochemically with an anti-p53 antibody, comparing its positive area with foci of microsatellite instability in each individual.

RESULTS

Alterations at one or more loci were observed in seven of 15 cancers (46.7%) and four of 15 intestinal metaplasias (26.7%). Two cases of replication error positive phenotype had no microsatellite alterations in their metaplastic mucosa. All the microsatellite alterations in the metaplastic mucosa were restricted to incomplete-type intestinal metaplasia around the respective cancers. Moreover, in one case, an identical pattern of microsatellite alteration was detected in the cancer tissue and in the adjacent metaplastic mucosa, suggesting the sequential development of gastric cancer from intestinal metaplasia. Frequent alteration was found at the locus D1S191 (1q), indicating that this locus might be altered early in the development of intestinal-type gastric cancer. No significant association between microsatellite instability and p53 immunoreactivity was observed in the cases examined.

CONCLUSION

These results indicate that microsatellite instability may be an early event in stomach carcinogenesis, especially in intestinal-type cancers.

Mutation frequencies at codon 248 of the p53 tumour suppressor gene are not increased in colon cancer cell lines with the RER+ phenotype

The replication-error positive (RER+) phenotype characterizes tumour cells with microsatellite instability. This 'mutator phenotype' is thought to induce spread mutations throughout the genome, thus increasing the risk of tumour development. Here we analyse spontaneously arising mutations at the tetranucleotide CCGG ( Msp I recognition site), at positions 14 067-14 070 of the p53 gene sequence, in three colon cancer cell lines, two with microsatellite instability and one without this characteristic. This restriction site covers hot-spot codon 248, which is often mutated in colon carcinomas. Using the Msp I RFLP-PCR assay we found that the mean mutation frequency at this site was not different among the cell lines considered. Taking the substitutions separately, none of the mutations involving codon 248 arose with significantly higher frequency in each of the RER+ cell lines (HCT116 and DLD1) compared with the RER-one (SW480). Only the CG transversion at nt 14 067 (codon 247) occurred with a slightly higher, but biologically insignificant, frequency in one of the RER+ cell lines (HCT116). Our in vitro data support the previously reported lack of correlation between microsatellite instability and p53 mutations in RER+ tumour specimens.

Rare occurrence of ras and p53 gene mutations in mouse stomach tumors induced by N-methyl-N-nitrosourea

The incidence of point mutations of H-, K- and N-ras and p53 oncogenes in male BALB/c mouse stomach tumors induced with N-methyl-N-nitrosourea (MNU) was examined by direct sequencing and PCR single-strand conformation polymorphism (PCR-SSCP). A mutation of GGT to AGT at K-ras codon 12 was found by SSCP in one adenocarcinoma from a total of 19 specimens including 5 adenocarcinomas, 9 adenomatous hyperplastic regions, 1 squamous cell carcinoma and 4 normal-like stomach regions from 4 mice. No mutations were detected by direct sequencing of H-, K- and N-ras oncogenes at exons 1 (codons 12 and 13) and 2 (codon 61) in a total of 26 specimens comprising 10 adenocarcinomas, 10 adenomatous hyperplastic regions, 2 squamous cell carcinomas and 4 normal-like stomach regions from 6 mice. No mutations were detected by direct sequencing of p53 oncogene at exons 5, 6, 7 and 8 in a total of 30 specimens including 13 adenocarcinomas, 8 adenomatous hyperplastic regions, 2 squamous cell carcinomas, 1 papilloma and 6 normal-like stomach regions from 7 mice. These results suggest that ras and p53 oncogenes do not play a role in mouse stomach carcinogenesis induced by MNU.

Expression of human telomerase RNA is an early event of stomach carcinogenesis

Expression of human telomerase RNA (hTR) and telomerase activity in gastric cancer and corresponding non-cancerous mucosa were studied. Telomerase activity was detected in 23 (88%) of 26 carcinoma tissues. Although all tumor specimens and non-cancerous mucosa expressed various levels of hTR, 21 (81%) of 26 cases expressed hTR at a higher level in the tumor than that in the corresponding mucosa. All 8 gastric carcinoma cell lines also expressed hTR at high levels. Nine (35%) of 26 non-cancerous mucosa showed telomerase activity and all of them contained intestinal metaplasia. The incidence of telomerase-positive mucosa in grade 2 intestinal metaplasia was significantly higher than that in grade 0 or grade 1 intestinal metaplasia, whereas hTR overexpression was found in grade 0 or grade 1 intestinal metaplasia as well as grade 2 intestinal metaplasia. The degree of Helicobacter pylori infection increased in parallel with the level of hTR expression and telomerase positivity. These results overall suggest that Helicobacter pylori infection may be a strong trigger for hTR overexpression in intestinal metaplasia, and this may lead to telomerase reactivation.