Stomach Carcinogenesis Research Articles

Reduced Expression of the TSP1 Gene and Its Association with Promoter Hypermethylation in Gastric Carcinoma

Thrombospondin-1 (TSP1) is a potent peptide shown in some tumor systems to be linked with angiogenesis. Epigenetic alteration of TSP1 has been reported in various primary tumors. However, the expression pattern of TSP1 has not been characterized in gastric carcinoma. We measured levels of TSP1 mRNA expression using quantitative RT-PCR in 30 gastric carcinomas and 10 non-neoplastic mucosae. In addition, we examined the correlation of the levels of TSP1 mRNA expression levels with promoter methylation status of TSP1 monitored by methylation-specific PCR as well as p53 mutation status detected by PCR-single-strand conformation polymorphism. Promoter hypermethylation of the TSP1 gene was found in 10 (33%) of 30 gastric carcinomas, and TSP1 mRNA expression levels were associated with promoter hypermethylation of TSP1 (p = 0.017; Mann-Whitney U test). p53 mutation was found in 5 (17%) of 30 gastric carcinomas, however, TSP1 mRNA expression was not associated with p53 mutation status (p = 0.858; Mann-Whitney U test). There was no correlation between TSP1 mRNA expression levels and T grade, N grade, tumor stage, or histological type. Our results suggest that transcriptional inactivation of TSP1 by aberrant DNA methylation of the promoter region may participate partly in stomach carcinogenesis through TSP1 down-regulation.

Expression of integrin-linked kinase is closely correlated with invasion and metastasis of gastric carcinoma.

Integrin-linked kinase (ILK), a serine/threonine protein kinase, implicates in cellular control of cell-matrix interactions and cell proliferation that is associated with a highly invasive phenotype of certain tumors. To study whether ILK is involved in the development and progression of gastric carcinoma, we examined the expression of ILK in gastric carcinoma cell lines, primary gastric carcinomas and corresponding non-neoplastic mucosa using reverse-transcription polymerase chain reaction (RT-PCR) and immunohistochemistry and analyzed the relationship with clinicopathological parameters. The expression of ILK mRNA was detected in 4 of 5 gastric carcinoma cell lines and 22 of 35 (63%) microdissected tumor samples of primary gastric carcinoma using RT-PCR. The incidence of cases with ILK mRNA expression was significantly higher in scirrhous and intermediate type (82%) than in medullary type (44%) (P=0.0204). Significant association was detected between ILK mRNA expression and presence of nodal metastasis (P=0.0388). Immunohistochemically, strong expression of ILK protein (over 50% of tumor cells were positive) was detected in 69% (84/122) of primary gastric carcinomas, whereas no ILK expression was found in non-neoplastic gastric epithelia. Strong expression of ILK protein was significantly associated with scirrhous and intermediate type (P=0.0217), deep invasion of tumor cells in gastric wall (P=0.0006), and presence of nodal metastasis (P=0.0176). These results strongly suggest that ILK may participate not only in stomach carcinogenesis especially of scirrhous and intermediate types but also in invasion and metastasis of gastric carcinoma. ILK might be a novel molecular marker for aggressive gastric cancer.

Earlier Helicobacter pylori infection increases the risk for the N-methyl-N-nitrosourea-induced stomach carcinogenesis in Mongolian gerbils.

Helicobacter pylori (H. pylori) is now well known to be associated with stomach cancer, with infection during childhood rather than as an adult considered to be more important for carcinogenesis. To evaluate the difference in susceptibility to stomach carcinogenesis in relation to age of acquisition of H. pylori infection, we designed an experiment involving inoculation of H. pylori ATCC43504 followed by N‐methyl‐N‐nitrosourea (MNU) treatment at different ages. Four‐week‐ old male Mongolian gerbils (MGs) were divided into twelve groups. H. pylori was inoculated at 4, 18 and 32 weeks of age, as representatives of early, middle and late infection, respectively. Two weeks later, the animals were treated with MNU. Groups without H. pylori and/or MNU were included as controls. The incidences of adenocarcinomas at 52 weeks after the inoculation in the early (H. pylori+MNU), middle (H. pylori+MNU), and late (H. pylori+MNU) group were 60% (12/ 20), 18.4% (2/11), and 10% (2/20), respectively. The corresponding figures were 14.8% (4/27), 0% (0/11), and 0% (0/21) in the MNU‐alone groups. A higher titer of serum IgG for H. pylori and higher gastrin level were seen in the early‐infected compared to the middle and the late groups (P<0.01). The results clearly demonstrated that early acquisition of H. pylori significantly increases gastric chemical carcinogenesis with MNU, as compared to the case with later infection, possibly because of differences in host gastric mucosal factors and immunologic responses.

No mutations of the Bub1 gene in human gastric and oral cancer cell lines

Chromosomal instability is one of the most important characteristics underlying tumorigenesis. Certain colorectal cancers with chromosomal instability have been shown to have inactivation of a spindle assembly checkpoint party due to mutation of Bub1, a mitotic checkpoint gene. We performed sequencing analysis on reverse transcriptase-polymerase chain reaction (RT-PCR) product of the Bub1 cDNA (entire coding sequence) from 8 human gastric cancer cell lines. In addition, genomic PCR products of Bub1 exon 8, 10, 12, 15 and kinase domain from 9 oral cancer cell lines were analyzed by polymerase chain reaction-single-stand conformation polymorphism (PCR-SSCP). Although sequencing analysis of the Bub1 cDNA revealed several point mutations in 8 gastric cancer cell lines, we could not confirm the mutations by analyzing genomic DNA. Furthermore, genomic PCR-SSCP analysis revealed no mutations in exon 8, 10, 12, 15 and kinase domain of the Bub1 gene in any oral cancer cell lines examined. These results suggest that mutation of the Bub1 gene might not play a role in human stomach and oral carcinogenesis.

Appearance of osteonectin-expressing fibroblastic cells in early rat stomach carcinogenesis and stomach tumors induced with N-methyl-N'-nitro-N-nitrosoguanidine.

The present study was designed to define molecular alterations in the initiation stage of rat stomach carcinogenesis. Groups of male Lewis rats, 6 weeks old, were given drinking water with or without N‐methyl‐N′‐nitro‐N‐nitrosoguanidine (MNNG; 100 mg/liter). Total RNA was isolated from the stomach pyloric mucosa, and fluorescent differential display analysis was performed. A cDNA fragment of 125 bp encoding an extracellular matrix‐associated matricellular glycoprotein, osteonectin, was identified after 14 days of MNNG exposure. A severalfold increase in expression was observed after 14 and 27 days of MNNG exposure, as determined by northern blot and RT‐PCR. Immunohistochemistry revealed that osteonectin‐mAb‐stained flbroblastic cells appeared in interstitial tissue of pyloric mucosa. Additionally the gene expression of other extracellular matrix proteins, viz., collagen type III, fibronectin, osteopontin, proteoglycan NG2, laminin γ1 and S‐laminin, was also markedly increased, as determined by competitive RT‐PCR after 14 days of MNNG exposure. The gene expression of osteonectin and the six other extracellular matrix proteins was elevated in twelve stomach adenocarcinomas and adenomas induced by MNNG in Lewis and WKY rats. Osteonectin‐mAb‐stained flbroblastic cells were evident in interstitial tissue of stomach tumor. These results suggest that osteonectin‐expressing flbroblastic cells appear in the interstitial tissue of pyloric mucosa from the early initiation stage of rat stomach chemical carcinogenesis, and that this phenomenon probably plays a role in cancer development.

Dendritic cell appearance and differentiation during early and late stages of rat stomach carcinogenesis.

Dendritic cell appearance and differentiation during early and late stages of rat stomach carcinogenesis were studied in the pyloric mucosa. Young male rats were given drinking water with or without N‐methyl‐N′‐nitro‐N‐nitrosoguanidine (MNNG; 100 nig/liter) for 14 days. Use of competitive RT‐PCR and northern blotting showed that MNNG exposure induced 3‐to 4–fold greater expression of the genes for integrin β7 and integrin αE2 (identical with antigen OX–62, a dendritic cell marker), as well as three cytokines, IL–4, GM‐CSF and TNFα, in the stomach pyloric mucosa of resistant Buffalo rats compared to sensitive ACI rats. These genes were minimally expressed in control animals. The results confirm the appearance of dendritic cells in the target pyloric mucosa and suggest the possibility that dendritic cell differentiation and maturation are induced by various cytokines, at least in Buffalo rats. Competitive RT‐PCR showed expression of integrin αE2 and β7, MHC class II‐associated invariant chain (Ii), MHC class II, B7–1, CD28, GM‐CSF and TNFα genes in all 12 examined stomach adenocarcinomas and adenomas induced in male Lewis and WKY rats with 30 weeks' MNNG exposure, suggesting the presence of dendritic cells in tumors. OX–62 staining and western blotting for OX–62 also confirmed the presence of dendritic cells in tumors. However, the population of dendritic cells in tumors was less than that in the pyloric mucosa after 14 days' MNNG exposure. The present results suggest that immune defense involving dendritic cells is marshaled from the very early initiation stage during rat stomach cancer development, but is downgraded in developed tumors.

Profiling and selection of genes differentially expressed in the pylorus of rat strains with different proliferative responses and stomach cancer susceptibility.

Rat stomach cancers induced by N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) are widely used as a model of differentiated-type human stomach cancers. ACI/NJcl (ACI) rats show persistent and strong cell proliferation in response to gastric mucosal damage by MNNG while BUF/NacJcl (BUF) rats show transient and limited cell proliferation. This difference is considered as one of the mechanisms for the high susceptibility of ACI rats to MNNG-induced stomach carcinogenesis. To identify genes involved in the differential induction of cell proliferation, cDNA subtraction was performed using RNA isolated from the pylorus of ACI and BUF rats treated with MNNG. By the temporal patterns of their expressions, the isolated 16 genes were overviewed and clustered into groups. Expression of the genes in group 1 (such as MHC class I and class II genes and interferon-inducible genes Iigp, Mx2 and Ubd) was induced by MNNG treatment, and the genes in group 2 (such as cellular retinoic acid-binding protein II (CrabpII)) were constantly expressed regardless of MNNG treatment. Then, expression profiles among multiple rat strains were compared with the extents of induction of cell proliferation. Iigp, CrabpII and EST222005 were found to show relatively good accordance, and these three genes were considered as candidates for genes that control differential induction of cell proliferation. Presence of polymorphisms at the genomic DNA level was indicated for CrabpII and EST222005, and these two genes were considered to be better candidates than IIGP: It was shown that the temporal profiles and profiles among strains, taking advantage of animal models, are useful to select candidate genes from a collection of genes isolated by various genome-wide scanning methods.

Independent variation in susceptibilities of six different mouse strains to induction of pepsinogen-altered pyloric glands and gastric tumor intestinalization by N-methyl- N-nitrosourea

Strain differences in susceptibility regarding stomach carcinogenesis due to N-methyl- N-nitrosourea were examined in males of six strains of mice: BALB/cA (BALB), C57BL/6N (C57BL6), CBA/JN (CBA), C3H/HeN (C3H), DBA/2N (DBA/2), and CD-1 (ICR). The frequency of pepsinogen-altered pyloric glands (PAPGs), putative precancerous lesions, was highest (19.6±9.9%) in the BALB and lowest in the ICR (12.3±5.7%) mice ( P<0.05). Incidences of adenocarcinomas at week 52 were 59.3% (16 of 27) and 18.5% (5 of 27), respectively ( P<0.005). Invasion also tended to be deepest in BALB compared with the other strains. Intestinal alkaline phosphatase-positive intestinal type cells were observed heterogeneously in some hyperplasias, adenomas and adenocarcinomas consisting of gastric type cells. Thus, intestinalization appeared to occur at random in both non-neoplastic and monoclonal neoplastic lesions, making it unlikely that IAP-positive cells could be precursors of gastric tumors. In contrast, the data suggest a direct histogenetic role for the PAPG, a useful preneoplastic marker lesion in mouse strains.

Preneoplastic Changes of Stomach Cancer. Mice, Rats and Mongolian Gerbils.

Investigations of the clonal growth of gastric carcinomas clearly suggest that individual cancers are derived from single cells with multi-potential activities and that cellular differentiation of gastric cancer cells occurs secondarily. By mucin histochemistry, gastric cancer cells of each histological group could be clearly classified into a gastric type and an intestinal type. The present results suggest the independent induction of intestinal metaplasia and gastric cancers and the occurrence of change of phenotypic expression of tumor cells from the gastric type to the intestinal type during growth of tumors. The Pepsinogen altered pyloric gland (PAPG) detected immunohistochemically may be considered to be a preneoplastic change. Rare mutations of p53 and ras genes in rat and mouse stomach cancers were found and p53 knockout mice (-/-) are more susceptible than (+/-) or (+/+) mice to N-methyl-N-nitrosourea stomach carcinogenesis.

Cyclooxygenase-2 expression during carcinogenesis in the human stomach.

The prolonged use of non-steroidal anti-inflammatory drugs (NSAIDs) has been associated with a reduced risk of gastric cancer. The best-known target of these drugs is cyclooxygenase (COX); the COX-2 isoform is frequently up-regulated in gastric adenocarcinomas. Using the post-gastrectomy stomach as a model, the expression of COX-2 mRNA and protein has been investigated during tumour progression in the human stomach. COX-2 expression was comparable in gastric stump carcinomas and conventional gastric carcinomas and localized primarily to the cytoplasm of the neoplastic cells. COX-2 mRNA was elevated in biopsies containing intestinal metaplasia, as determined by reverse transcriptase polymerase chain reaction (RT-PCR). COX-2 immunopositivity became more frequent during progression from reactive epithelium to high-grade dysplasia, both in the epithelial and in the stromal cell compartment. Co-localization of COX-2-positive stromal cells was seen with CD68, alpha-smooth muscle actin (alpha-SMA), vimentin, and HLA-DR, but an as yet unidentified subpopulation of stromal cells remained. Co-localization with the macrophage marker CD68 was only observed in a minority of COX-2-positive cells. These data show that COX-2 expression is a relatively early event during carcinogenesis in the stomach. COX-2 expression increases during tumour progression in the stomach, suggesting a role for COX-2 expression in gastric tumourigenesis.

Alteration of cadherin isoform expression and inhibition of gap junctions in stomach carcinoma cells

To explore cell malignant phenotype correlated changes of cell surface adhesion molecules and cell-cell communication in carcinogenesis, human stomach transformed and cancer cell lines were investigated. Expressions of E-cadherin, N-cadherin, α-catenin, β-catenin as well as gap junction (GJ) protein Cx32 were studied by utilization of immunoblotting, immunocytochemical and fluorescent dye transfer methods. Mammalian normal stomach mucosal cells expressed E-cadherin but not N-cadherin. E-cadherin immunofluorescence was detected at cell membranous adherens junctions (AJ) where colocalization with immunofluorescent staining of inner surface adhesion plaque proteins αand β-catenins was observed. The existence of E-cadherin/ catenin (α-, β-) protein complexes as AJ was suggested. In transformed and stomach cancer cells E-cadherin was inhibited, instead, N-cadherin was expressed and localized at membranous AJ where co-staining with α-and β-catenin fluorescence was observed. Formation of N-cadherin/catenin (α-, β-) protein complex at AJs of transformed and cancer cells was suggested. The above observations were further supported by immunoblotting results. Normal stomach muscosal and transformed cells expressed Cx32 at membranous GJ and were competent of gap junction communication (GJIC). In stomach cancer cells, Cx32 was inhibited and GJIC was defective. The results suggested that changes of signal pathways mediated by both cell adhesion and cell communication systems are associated intracellular events of stomach carcinogenesis. The alteration of cadherin isoform from E-to N-cadherin in transformed and stomach cancer cells is the first report.

Promoting effects of combined antioxidant and sodium nitrite treatment on forestomach carcinogenesis in rats after initiation with N-methyl- N′-nitro- N-nitrosoguanidine

The effects of sodium nitrite (NaNO 2), in combination with one of three antioxidants, tert-butylhydroquinone (TBHQ), α-tocopherol (α-Toc) and propyl gallate (PG), on N-methyl- N′-nitro- N-nitrosoguanidine (MNNG) stomach carcinogenesis were investigated in F344 rats. Groups of 15 male rats were treated with an intragastric dose of 150 mg/kg body weight of MNNG, and starting 1 week later, were treated with 0.5% TBHQ, 1% α-Toc, 1% PG or basal diet with or without 0.2% NaNO 2 in their drinking water until they were killed at the end of week 36. Macroscopically, in MNNG-treated animals, combined administration of α-Toc or PG with NaNO 2 significantly increased the areas and numbers of forestomach nodules as compared with the respective antioxidant alone values. Microscopically, in MNNG-treated animals, treatment with TBHQ significantly increased the incidence and multiplicity of forestomach papillomas as compared with basal diet alone value. Combined administration of α-Toc with NaNO 2 significantly raised the multiplicity of forestomach papillomas, with a tendency to elevation in the incidence as compared with the group given α-Toc alone. Incidences of forestomach moderate and/or severe hyperplasias were significantly higher in the TBHQ or PG plus NaNO 2 groups than in the single compound groups. In rats without MNNG treatment, combined treatment of antioxidants with NaNO 2 significantly increased the incidences of mild or moderate hyperplasia. In the glandular stomach, although the incidence of atypical hyperplasia showed a non-significant tendency for decrease with TBHQ treatment, additional administration of NaNO 2 caused significant increase. These results indicate that co-administration of NaNO 2 with α-Toc, TBHQ or PG and particularly the first, promotes forestomach carcinogenesis. Concurrent α-Toc, TBHQ or PG treatment with NaNO 2 is likely to induce forestomach tumors in the long term.

Assessment of differential expression of oncogenes in gastric adenocarcinoma by fluorescent multiplex RT-PCR assay.

We screened samples of tumour and peripheral normal tissue for differential expression of oncogenes by using an approach of detecting the differences in expression of a number of oncogenes simultaneously. Total RNA was isolated from 29 pairs of normal and tumour tissue samples from patients with gastric adenocarcinoma. Seven pairs of primers for oncogenes most probably associated with the process of carcinogenesis in stomach including cyclin E, c-erbB-3, HGR, c-met, TDGF/cripto, FGF-4, and EGF were used for the construction of fluorescent multiplex RT-PCR. Sense primers were 5' end-labelled with a fluorescent dye. 5-7 gastric oncogenes were simultaneously analysed for overexpression. Multiplex reverse transcription with a set of unlabeled primers was followed by a PCR reaction by adding the corresponding set of fluorescent labelled PCR-primers. Expression of oncogenes was compared to GAPDH internal standard. Multiplex fluorescent RT-PCR results were analysed by capillary electrophoresis on ABI-PRISM 310 Genetic Analyzer. Differential expression of oncogene mRNAs in tumour and normal tissue was assessed by comparison of oncogene/GAPDH ratios in tumours and their peripheral normal mucosa. Our results show, that in most patients, comparing to normal tissue, we could estimate overexpression of at least one oncogene in a sample.

No mutations of the Bub1 gene in human gastric carcinomas.

Chromosomal instability in colorectal cancers is associated with functional loss of a mitotic check point partly due to mutations of the Bub1, one of the mitotic check point genes. However, mutation of coding sequences of human Bub1 gene has not been fully elucidated in gastric carcinomas. We performed sequencing analysis on reverse transcriptase-polymerase chain reaction (RT-PCR) product of the Bub1 cDNA (entire coding sequence) from 5 human gastric carcinomas as well as on genomic PCR products of Bub1 kinase domain from 7 gastric carcinoma tissues. Although sequencing analysis of the Bub1 cDNA revealed several point mutations in 2 gastric carcinoma cases, we could not confirm the mutations by analyzing genomic DNA. Furthermore, genomic DNA sequencing revealed no mutations in the kinase domain of the Bub1 gene in any gastric carcinoma examined. These results suggest that mutational inactivation of the Bub1 gene might not play a key role in human stomach carcinogenesis.

Das gastral differenzierte Magenadenokarzinom

Gastric carcinomas are classified histogenetically into diffuse and differentiated types. The latter are often referred to as intestinal-type carcinomas and are believed to originate from intestinal metaplasia. However, histogenetic studies on smaller and initial lesions of the differentiated adenocarcinoma do not support this. From phenotypical expressions of neoplastic lesions arising in hyperplastic polyps of the stomach we first proposed an entity of gastric-type adenocarcinomas, which has been widely accepted. Our recent mucin and immunohistochemical investigations reveal that most smaller adenocarcinomas retain gastric-type differentiation and that those of the exclusively intestinal phenotype are rather rare. On the other hand, most adenomas are strongly and extensively positive for intestinal marker, indicating that the adenoma-carcinoma sequence is not a common event in the stomach carcinogenesis. Other studies show that the expression of intestinal mucin or carbohydrate antigen as expressed in intestinal metaplasia is manifested more extensively in carcinoma cells in larger tumors. It is suggested that intestinalization of tumor cells is a time-dependent phenomenon. Differential gene abnormalities between gastric- and intestinal-type carcinomas of the stomach are discussed, regarding their histogenesis and progression.

Dose-dependent induction of glandular stomach preneoplastic and neoplastic lesions in male F344 rats treated with catechol chronically.

The dose-dependence of catechol glandular stomach carcinogenesis was investigated in male F344 rats. Groups of 30 male animals were fed catechol at dietary levels of 0 (control). 0.1, 0.2, 0.4, and 0.8% for up to 104 weeks. Five rats of each group were killed at 34 weeks and the remaining animals were sacrificed at the termination, all undergoing histopathological examination. Moderate retardation of body weight increase was observed in the 0.8% group. but no adverse effects were found in terms of survival. Submucosal hyperplasias and adenomas of the pyloric glands developed in the 0.4 and 0.8% groups, only very minor changes being noted in the 0.1 and 0.2% groups at week 34. Incidences of adenocarcinoma development in the pylorus were 4% and 8% in 0.4% and 0.8% groups, respectively, and 0 in the 0.1% and 0.2% groups, at the termination. Adenomas and submucosal hyperplasias were found in nearly all animals fed 0.2% catechol or more, the incidences of those in 0.1% group being 0% and 56%, respectively. Serum gastrin levels were significantly increased in the 0.2, 0.4, and 0.8% groups at 34 weeks, and in all treated groups at the termination, at extents comparable with the induction of proliferative lesions in the pylorus. The results thus demonstrated that dietary levels of 0.4% and 0.8% catechol long-term induce adenocarcinomas in the pyloric glands, while 0.1 and 0.2% cause benign proliferative lesions, all accompanied by increase in serum gastrin levels. As a no-effect level could not be decided in the present study, further investigation of lower doses is needed to determine whether a threshold exists.

Carcinogenic potential of duodenal reflux juice from patients with long-standing postgastrectomy.

To determine whether study on the carcinogenic potential of reflux juice from patients with remote gastrectomy could clarify the inherent relationship between duodenal reflux and gastric stump cancer. A total of 37 reflux juice samples (13 Billroth I, 24 Billroth II) were employed in the present study. A two-stage transformation assay using BALB/c 3T3 cells was carried out to test the initiating or promoting activity of these samples. Two of 18 (11.1%) reflux samples exerted initiating activities, whereas 9/19 (47.4%) samples enhanced the MNNG-initiating cell transformation, suggesting the duodenal reflux juice might more frequently possess the tumor-promoter activity (P = 0.029). In addition, there was no difference in initiating activities of the samples irrespective of surgical procedures (P = 0.488), while Billroth II samples exhibited stronger tumor-promoter activity than Billroth I samples (P = 0.027). Furthermore, the promoter activities were well correlated with the histological changes of the stomas (r(s) = 0.625, P = 0.004), but neither their cytotoxicities nor initiating activities had this correlation (Probabilities were 0.523 and 0.085, respectively). The duodenal reflux juice from patients with remote postgastrectomy did have carcinogenic potential, and suggested that tumor-promoting activity should principally account for the high incidence of gastric cancer in gastrectomy patients. In contrast, it is difficult to explain the high stump-cancer incidence with the N-nitroso compounds theory-a popular theory for the intact stomach carcinogenesis, and it seemed to be justified to focus chemo-prevention of this cancer on the tumor-promoting potential of reflux juice.

Cell proliferation in type C gastritis affecting the intact stomach

Aims—Type C gastritis caused by bile reflux has a characteristic appearance, similar to that seen in other forms of chemical gastritis, such as those associated with NSAIDs or alcohol. An...

Seventh Japanese–German workshop on molecular and cellular aspects of carcinogenesis

Seventh Japanese–German workshop on molecular and cellular aspects of carcinogenesis

Relation between food habits and p53 mutational spectrum in gastric cancer patients.

p53 tumour suppressor gene mutations were analysed in gastric cancer in relation to food habits and social class in 56 patients from a high risk region of Italy. Exons 5-8 were analysed with DGGE method on amplified DNA from formalin-fixed paraffin-embedded samples. All p53 mutations were observed in patients belonging to low social class and the majority of mutations were found in intestinal type cancers. A positive association was also found with low raw vegetables, fresh, dried and preserved fruits, and ascorbic acid intake. Moreover, specific types of mutations were significantly associated with particular factors, thus suggesting the presence of specific molecular etiologic process in stomach carcinogenesis.