Evidence for a common molecular pathogenesis in colorectal, gastric, and pancreatic cancer

Genetics, Genomics and Emerging Molecular Therapies of Pancreatic Cancer

The number of cases of pancreatic cancers in 2019 in Poland was 3852 (approx. 2% of all cancers). The course of the disease is very fast, and the average survival time from the diagnosis is 6 months. Only <2% of patients live for 5 years from the diagnosis, 8% live for 2 years, and almost half live for only about 3 months. A family predisposition to pancreatic cancer occurs in about 10% of cases. Several oncogenes in which somatic changes lead to the development of tumours, including genes BRCA1/2 and PALB2, TP53, CDKN2A, SMAD4, MLL3, TGFBR2, ARID1A and SF3B1, are involved in pancreatic cancer. Between 4% and 10% of individuals with pancreatic cancer will have a mutation in one of these genes. Six percent of patients with pancreatic cancer have NTRK pathogenic fusion. The pathogenesis of pancreatic cancer can in many cases be characterised by homologous recombination deficiency (HRD)-cell inability to effectively repair DNA. It is estimated that from 24% to as many as 44% of pancreatic cancers show HRD. The most common cause of HRD are inactivating mutations in the genes regulating this DNA repair system, mainly BRCA1 and BRCA2, but also PALB2, RAD51C and several dozen others.

Familial Adenomatous Polyposis Syndrome: An Update and Review of Extraintestinal Manifestations

CONTEXT.—

Familial adenomatous polyposis (FAP) is a rare genetic disorder with autosomal dominant inheritance, defined by numerous adenomatous polyps, which inevitably progress to colorectal carcinoma unless detected and managed early. Greater than 70% of patients with this syndrome also develop extraintestinal manifestations, such as multiple osteomas, dental abnormalities, and a variety of other lesions located throughout the body. These manifestations have historically been subcategorized as Gardner syndrome, Turcot syndrome, or gastric adenocarcinoma and proximal polyposis of the stomach. Recent studies, however, correlate the severity of gastrointestinal disease and the prominence of extraintestinal findings to specific mutations within the adenomatous polyposis coli gene (APC), supporting a spectrum of disease as opposed to subcategorization. Advances in immunohistochemical and molecular techniques shed new light on the origin, classification, and progression risk of different entities associated with FAP.

OBJECTIVE.—

To provide a comprehensive clinicopathologic review of neoplastic and nonneoplastic entities associated with FAP syndrome, with emphasis on recent developments in immunohistochemical and molecular profiles of extraintestinal manifestations in the thyroid, skin, soft tissue, bone, central nervous system, liver, and pancreas, and the subsequent changes in classification schemes and risk stratification.

DATA SOURCES.—

This review will be based on peer-reviewed literature and the authors' experiences.

CONCLUSIONS.—

In this review we will provide an update on the clinicopathologic manifestations, immunohistochemical profiles, molecular features, and prognosis of entities seen in FAP, with a focus on routine recognition and appropriate workup of extraintestinal manifestations.

Influence of deleted in colorectal carcinoma gene on proliferation of ovarian cancer cell line SKOV-3 in vivo and in vitro

OBJECTIVE

To elucidate the effects of the deleted in colorectal carcinoma (DCC) gene on proliferation of ovarian cancer cell line SKOV-3.

METHOD

An exogenous recombinant eukaryotic expression vector pcDNA3.1(+)-DCC, containing human DCC cDNA coding sequences, was constructed and transfected into SKOV-3 cells (SKOV-3/DCC). The pcDNA3.1 (+) transfected cells (SKOV-3/Neo) and SKOV-3 cells were used as the positive and negative controls, respectively. Expressions of DCC mRNA and protein were analyzed by RT-PCR and immunocytochemical analysis, respectively. Cell growth was detected by soft agar colony formation assay and MTT assay. Flow cytometry and transmission electron microscopy were used to assess the effects of DCC on cell cycle distribution and ultrastructure, respectively. BALB/c mice were used to evaluate the effects of DCC on tumorigenicity in vivo.

RESULTS

RT-PCR and immunocytochemical analysis revealed the exogenous DCC gene was successfully transfected into SKOV-3 cell lines and obtained permanent expression. The half maximal inhibitory concentration (IC50) of SKOV-3/DCC cells was significantly lower than that of SKOV-3 or SKOV-3/Neo cells (all P<0.05). DCC expression caused SKOV-3 cells to be arrested in G1 phase (78.0%), and electron microscopic analysis showed SKOV-3/DCC cells displayed typical morphological changes of apoptosis. Two mice xenografted with SKOV-3/DCC cells showed no tumor tumorigenecity. The tumor volume of BALB/c mice bearing SKOV-3/DCC cells (3.403 mm(3)) was smaller than that of SKOV-3 cells (9.206 mm(3)).

CONCLUSION

DCC gene may play an important role in suppressing the growth of SKOV-3 cell line and inducing apoptosis.

Microsatellite instability and loss of heterozygosity of tumor suppressor genes in Bosnian patients with sporadic colorectal cancer

Considering its frequency, high mortality rate as well as many etiological mysteries colorectal cancer is a challenge to contemporary science. In our study we analyzed RER + and RER--phenotypes and their relations with clinical-pathological characteristics of sporadic colorectal cancers. We also analyzed genetic alterations of tumor suppressor genes as well as their relation with microsatellite instability. The study was based on 54 tumor samples and 54 samples of the surrounding healthy tissue of patients with colorectal cancer. According to Amsterdam Criteria and Bethesda Criteria 35/54 or 64,81% belonged in the group of sporadic colorectal cancer. Mononucleotide marker Bat 25 showed instability in 48,57%; Bat 26 in 45,71% and Bat 40 in 29/35 82,86% of tumor samples. Considering dinucleotide markers, TP 53 showed instability in 54,29% and DS123 in 37,14% of tumor samples. Genetic alterations in tumor suppressor genes were found in tumor tissue: NM 23 in 54,29% samples, p53 in 51,43%, APC in 51,43%, DCC2 in 34,29%, RB1 in 22, 86% and DCC 1 in 28,57%. Our studies confirmed that genetic instability had an important role in the development of tumor type. Our results showed that mononucleotide marker Bat 40 might be used for an easy and fast screening procedure in Bosnian population, because it exhibited high percent of microsatellite instability and was in relation with RER+ phenotype. This investigation showed that different genetic alterations may occur during cancer development in each individual patient's tumor. These changes result in MMR inactivation, which causes RER+ phenotype. Our results suggest a connection between alteration in some tumor suppressor genes and MSI phenotype of sporadic colorectal cancer in Bosnian population.

High-Grade Pancreatic Intraepithelial Neoplasia in a Patient With Familial Adenomatous Polyposis

Familial adenomatous polyposis (FAP) is caused by mutation of the adenomatous polyposis coli (APC) gene and is characterized by multiple colorectal adenomas and tumors of other organs and sites. A 58-year-old woman with FAP syndrome and previous total colectomy presented for routine follow-up examination. Abdominal ultrasound and subsequent endoscopic evaluation revealed ampullary and duodenal polyps, as well as inhomogeneity of the pancreatic head. A pancreaticoduodenectomy confirmed multiple duodenal adenomas. In addition, high-grade pancreatic intraepithelial neoplasia (PanIN-3) was found in the smaller pancreatic ducts. Pancreatic precancerous lesions have only rarely been described in FAP, including 2 pancreatic duct adenomas and 2 intraductal papillary mucinous neoplasms. A review of the world English literature revealed no reports of PanIN-3 in association with FAP. Further studies are required to determine if patients with FAP are at increased risk for pancreatic premalignant lesions.

Three independent genetic profiles based on mucin expression in early differentiated-type gastric cancers--a new concept of genetic carcinogenesis of early differentiated-type adenocarcinomas

Recent molecular studies have shown that the genetic profiles of differentiated-type adenocarcinomas of the stomach are associated with distinct cellular mucin phenotypes (gastric- intestinal- and mixed-phenotypes). Therefore, we examined whether these cellular mucin phenotypes reflect specific molecular genetic alterations, and whether the phenotypes can be used to help categorize the intramucosal neoplasias of gastric tumors. We subclassified tumors into four cellular phenotypes using immunohistochemical mucin analysis. In all, 62 early gastric carcinomas (gastric-phenotype, 13; intestinal-phenotype, 17; mixed-phenotype, 31; unclassified-phenotype, 1) were examined using a combination of polymerase chain reaction microsatellite assays and immunohistochemical analysis in order to detect chromosomal allelic losses of multiple cancer-related chromosomal loci (1p, 3p. 4p, 5q, 8p, 9p, 13p, 17p, 18q and 22q), microsatellite instability (MSI), and overexpression of the p53 protein. In addition, we analyzed the relationship between MSI status and hMLH1 promoter hypermethylation, which is thought to be a cause of high MSI status. For gastric phenotype cancers, the frequency of 3p allelic loss was higher than that of other microsatellite markers, whereas 5q allelic loss was frequently found in intestinal phenotype cancers. The genetic profile of mixed phenotype cancers is comprised of two distinct genetic types: LOH and MSI types. In the former, 5q, 3p and 18q allelic losses are seen frequently in intramucosal carcinomas. On the other hand, 17p, 1p and 9p allelic losses are associated with the development of submucosal carcinomas. MSI was observed only in mixed phenotype cancers (six of 31 mixed phenotype cancers). Overexpression of the p53 protein is common in differentiated-type gastric cancers. In addition, the MSI status of the tumor cells was correlated with the extent of hypermethylation of the hMLH1 promoter. We suggest that the cellular mucin phenotypes of the differentiated-type adenocarcinomas result from distinct genetic alterations.

APC gene expression in gastric carcinoma: an immunohistochemical study

Gastric carcinoma is one of the most common malignancies worldwide, particularly in Japan and China. Inactivation of the adenomatous polyposis coli ( ) gene, a tumor suppressor gene, has been shown to play a significant role in the development of colorectal carcinoma, and it has been suggested that it may play a role throughout the digestive tract, including the stomach. This study assesses gene expression in normal gastric mucosa and gastric adenocarcinoma using an antibody to the C-terminal region. One hundred twenty cases of gastric adenocarcinoma were examined from the files of Beaumont Hospital, Dublin, Ireland, and China Medical University, Shenyang, China. Ninety-one cases were informative. Of these, 78% revealed loss of staining. Loss of staining in adenocarcinoma showed no association with tumor type, tumor, stage or patient nationality. Loss of staining was also found in nine of 35 cases (26%) of intestinal metaplasia. In conclusion, loss of the gene, as determined by immunohistochemical staining, appears to be an early event in gastric carcinogenesis. Immunohistochemistry is a sensitive method for detection of this loss.

Adenomatous polyposis coli gene mutation and decreased wild-type p53 protein expression in oral submucous fibrosis: a preliminary investigation

OBJECTIVE

The purpose of this study was to identify the adenomatous polyposis coli (APC) tumor suppressor gene mutation and level of wild-type p53 protein expression in patients with oral submucous fibrosis (OSF).

STUDY DESIGN

Cells from OSF and control subjects were cultured in Dulbecco modified Eagle medium with 10% fetal bovine serum at 37 degrees C. Genomic DNA was extracted from cultured cells and used as a template for polymerase chain reaction amplification of the APC tumor suppressor gene. The presence of wild-type p53 protein in cell lysates of cultured cells was analyzed by Western blot. Data were analyzed by the sign test for nonparametric samples and by analysis of variance.

RESULTS

The results showed that the APC gene of explant cultured cells from OSF patients (8/8) had a CGA-to-GGA transition mutation at codon 498 that resulted in an Arg-to-Gly missense mutation (P <.01). All (8/8) normal HGF cultures revealed expression of the wild-type APC protein. Cells cultured from 7 of 8 OSF patients were also found to have a single nucleotide deletion at nucleotide 1494 that resulted in creating a stop codon (TGA) at codon 504 (P <.01). This created a premature signal for the endpoint of translation and thus resulted in the generation of a truncated protein product that encodes a polypeptide of 503 amino acid residue. It was found that wild- type p53 protein in human gingival fibroblast cell cultures was significantly higher than in OSF cells (P <.01).

CONCLUSION

Alterations of the APC and wild-type p53 tumor suppressor genes in OSF may imply a risk for progression to oral cancer.

Alterations of K-ras and p53 mutations in colorectal cancer patients in Central Europe

Many molecular investigations of colorectal cancer (CRC) have suggested that the accumulation of specific mutations in proto-oncogenes and tumor suppressor genes regulating cell growth via signal transduction trigger the stagewise progression to malignancy. In this study, the frequency, location, and type of mutations of the K-ras proto-oncogene exon I and p53 tumor suppressor gene exons 5-8 were analyzed in colorectal carcinomas of 65 patients from Central Europe, using polymerase chain reaction (PCR)-cold single-strand conformation polymorphism (SSCP) screening and direct sequencing. The incidence of K-ras activating mutations in these Central European samples was lower (25%) compared to that obtained in American and western European populations (40-50% at least), while the incidence of p53 inactivating mutations was similar (58%). These results suggest that some other genetically linked mechanisms may play a role in CRC development and progression, and hence K-ras and p53 mutations cannot be considered to be universal genetic markers for CRC.

Use of crypt isolation to determine loss of heterozygosity of multiple tumor suppressor genes in colorectal carcinoma

Analysis of loss of heterozygosity (LOH) is very important in the study of tumor suppressor genes. However, accurate LOH analysis of tumor suppressor genes is difficult because of dilution by contaminating non-tumor DNA. Thus, enrichment of tumor DNA is required to accurately determine LOH of the tumor. We developed a new application of the fluorescent polymerase chain reaction by coupling it with crypt isolation to accurately assess the incidence of LOH of tumor suppressor genes in 45 colorectal carcinomas. LOH was observed at p53 in 26 of 37 tumors (70.3%), at APC in 13 of 35 (37.1%), at DCC in 16 of 25 (64.0%), at NF-2 in 5 of 23 (21.7%), and at nm23 H-1 in 7 of 30 (23.3%). We could clearly determine LOH of these genes because the crypt isolation technique was used. Although the incidence of LOH at each of these loci, as determined by using this technique, was similar to that obtained in previous studies using conventional methods, this method provides a simpler, more accurate way to assess LOH. In addition, the morphology of the samples can be analyzed before genetic analysis.

Suppressed tumorigenicity of human endometrial cancer cells by the restored expression of the DCC gene

To obtain functional evidence for DCC as a tumour suppressor associated with endometrial cancer, the human DCC cDNA encoding a complete open reading frame (ORF) was transfected into highly tumorigenic human endometrial carcinoma cells, HHUA and Ishikawa in which DCC expression was completely deleted. Reconstituted expression of DCC in HHUA had little effect on in vitro growth, but suppressed tumour formation in mice completely. The clones from Ishikawa had abundant DCC expression similar to that in normal endometrium. Their growth in vitro was suppressed and showed apoptotic phenotype. Lower levels of DCC expression in the prolonged passaged clones did not induce apoptosis, but still had the potential to suppress tumorigenicity. These observations imply a role of DCC in regulation of normal endometrial cell growth, and categorize DCC as the tumour suppressor gene for endometrial cancer.

Molecular aspects of ovarian cancer. Is gene therapy the solution?

Genetic abnormalities of cancer cells are complex and usually nonspecific. Genetic anomalies specific to ovarian cancer have not been reported. This article focuses on what molecular anomalies are known in ovarian cancer and describes the first trials that have used transfer of genes to reestablish a normal cellular function in this disease. Suicide gene therapy has been the prototype of this new therapeutic approach.

The use of molecular technology in the differentiation of pancreatic cancer and chronic pancreatitis

CONCLUSION

It is concluded that currently there are limitations in the use of some of the proposed tests, whereas in the future, further progress in our understanding of the molecular biology of pancreatic disease and the development and application of existing techniques should have a greater impact on clinical practice.

BACKGROUND

Fifteen to 20% of patients with pancreatic cancer present with a resectable mass in the head of the pancreas, but there is a subgroup of patients for whom it is difficult to reach the correct diagnosis.

METHOD

This article addresses how molecular technology can be used to aid in the diagnosis of this group of patients. The clinical and scientific literature is reviewed by accessing papers through the Medline database.

RESULTS

This article reviews the limitations of conventional imaging techniques and the limitations of fine needle aspiration cytology and cytological examination of pancreatic duct secretions. The molecular biology of both pancreatic cancer and chronic pancreatitis is then reviewed with emphasis on the common molecular defects seen in these diseases. The current use of molecular techniques in the examination of cytological and histological specimens, stool, blood, and pancreatic duct secretions and how this helps discriminate between benign and malignant lesions of the pancreas is addressed. Finally, the use of novel serum screening tests in groups at high risk of pancreatic cancer is discussed.

Prevalence of activating K-ras mutations in the evolutionary stages of neoplasia in intraductal papillary mucinous tumors of the pancreas

OBJECTIVE

The purpose of the study was to determine the prevalence of activating K-ras mutations in the pancreas of patients with intraductal papillary mucinous tumors (IPMT) and to analyze their relation to the degree of site-specific histopathologic abnormality.

BACKGROUND

Intraductal papillary mucinous tumors of the pancreas have a biologic behavior that is significantly different from pancreatic ductal adenocarcinoma. Activating K-ras mutations, which may be important events in a multistage process of carcinogenesis, have been reported in IPMT.

METHODS

Forty-six different histologic specimens (comprising normal pancreatic ducts, hyperplasia, low-grade dysplasia, high-grade dysplasia-carcinoma in situ, and carcinoma) from 16 patients with IPMT and 9 specimens from patients with pancreatic ductal adenocarcinomas were designated by a pathologist. Genomic DNA was extracted from paraffin-embedded tissue sections after microdissection. The K-ras gene was amplified by polymerase chain reaction and subjected to DNA sequencing.

RESULTS

The K-ras mutations were detected in at least one specimen in 13 (81.2%) of 16 patients with IPMT. All mutations were found in codon 12. No codon 13 mutations were detected. The relative frequency of K-ras mutations in the different stages of IPMT was 16.7% in normal epithelium and papillary hyperplasia, 28.6% in low-grade dysplasia, and 57.1% in high-grade dysplasia-carcinoma in situ and invasive carcinoma. The K-ras mutations were detected in 6 (66%) of 9 pancreatic ductal adenocarcinomas.

CONCLUSIONS

The K-ras codon 12 point mutations are as frequent in IPMT as in ductal adenocarcinoma. A stepwise increase in the frequency of codon 12 mutations correlated with the stage of neoplastic evolution to cancer. This finding is consistent with an important role of K-ras gene mutations in the transformation from normal epithelium to invasive carcinoma in the majority of patients with IPMT.

Mapping of a breast cancer tumor suppressor gene locus to a 4-cM interval on chromosome 18q21

DPC4 and DCC, putative tumor suppressor genes implicated in the genesis of several types of human cancer, lie on the long arm of human chromosome 18. We examined 200 primary breast cancers for allelic losses on chromosome 18, using 15 microsatellite markers distributed along the long arm. Allelic loss was detected most frequently (29-30%) at loci mapped to 18q21. Deletion mapping of the 34 tumors showing partial or interstitial deletions identified a commonly deleted region within the 4-cM interval flanked by D18S474 and D18S487 at 18q21.1-q21.3. Although this interval included the DPC4 and DCC genes, we excluded DPC4 from candidacy when polymerase chain reaction-single-strand conformation polymorphism analysis of each exon failed to detect abnormalities in any of the 54 breast cancers that exhibited loss of heterozygosity involving 18q. Allelic loss on 18q was found more frequently in tumors of the solid tubular histological type (24 of 55, 44%) than in other types (24 of 113, 21%) (P = 0.0049). The results suggest that a tumor suppressor gene located within the 4-cM region at 18q21, either DCC or another gene not yet identified, may play a role in the development of some sporadic breast cancers, particularly those of the solid tubular type.

The interactions of APC, E-cadherin and beta-catenin in tumour development and progression

Much progress has been made in identifying genes mutated during the development of colorectal carcinoma. Mutation of the APC gene in particular appears to be fundamental for colorectal tumour initiation. In contrast, loss of expression of E-cadherin appears to be a late event, which may be important in the development of invasion. Recent clarification of the function of APC, however, has shown that it exists in equilibrium with beta-catenin and E-cadherin. This review discusses the function of these molecules, their interactions, and how APC mutations may alter the equilibrium with beta-catenin and E-cadherin. It is argued that these changes cause aberrant architectural development of tissue, which results in loss of growth control. It is this escape from growth control, rather than acquisition of cell-autonomous growth, which results in the initial development of adenomas. The role of the E-cadherin-catenin unit in colorectal tumour invasion is discussed and the evidence is reviewed for the involvement of APC and E-cadherin in tumours arising from non-intestinal epithelia.

The interactions of APC, E-cadherin and beta-catenin in tumour development and progression

Much progress has been made in identifying genes mutated during the development of colorectal carcinoma. Mutation of the APC gene in particular appears to be fundamental for colorectal tumour initiation. In contrast, loss of expression of E-cadherin appears to be a late event, which may be important in the development of invasion. Recent clarification of the function of APC, however, has shown that it exists in equilibrium with beta-catenin and E-cadherin. This review discusses the function of these molecules, their interactions, and how APC mutations may alter the equilibrium with beta-catenin and E-cadherin. It is argued that these changes cause aberrant architectural development of tissue, which results in loss of growth control. It is this escape from growth control, rather than acquisition of cell-autonomous growth, which results in the initial development of adenomas. The role of the E-cadherin-catenin unit in colorectal tumour invasion is discussed and the evidence is reviewed for the involvement of APC and E-cadherin in tumours arising from non-intestinal epithelia.

Studies on the relationship between the point mutation of ras oncogenes and the prognosis of patients with gastric cancer

AIM: To study the relationship between the point mutation of ras oncogenes and the prognosis of patients with gastric cancer.

METHODS: The point mutations at codon 12 and 61 of c-Ha-ras, at codon 12 and 13 of K-ras, and at codon 12 of N-ras were studied with PCR-RFLP in 88 formalin fixed and paraffin embedded specimens of gastric cancer.

RESULTS: It was found that the overall rate of point mutation of ras oncogenes was 18.2% and the positivity of the point mutation of ras oncogenes was related to the cancerous invasion of the serosa, the status of lymph node metastasis, the stage of cancer and the survival time after surgery.

CONCLUSION: The findings suggest that the determination of point mutations of ras oncogenes can be used to determine the prognosis of patients with gastric cancer.

Allelotype analysis of adenocarcinoma of the gastric cardia

To identify chromosomal loci involved in the development of proximal gastric adenocarcinoma, this study delineated the pattern of allelic imbalance in a series of 38 adenocarcinomas arising in the gastric cardia. A total of 137 microsatellite markers covering all autosomal arms, excluding acrocentric arms, were analysed. A mean of 35 out of a total of 39 chromosomal arms studied were informative for each patient. The tumour group demonstrated a high level of allelic imbalance, with an observed median fractional allelic imbalance of 0.47 for the 29 intestinal-type adenocarcinomas and 0.54 for the nine diffuse-type adenocarcinomas. Allelic imbalance was detected in >50% of informative cases in both histological subtypes on a number of chromosomal arms. In the intestinal subtype, these included, 3p (61%), 4q (71%), 5q (59%), 8p (60%), 9p (65%), 9q (83%), 12q (52%), 13q (52%), 17p (78%) and 18q (70%). A higher incidence of allelic imbalance was detected on chromosome 16q in tumours of the diffuse type relative to those of the intestinal type. A more detailed mapping on chromosomes 4q and 6q identified a number of cases with subchromosomal breakpoints. In conclusion, this analysis has indicated regions of the genome potentially involved in the development of proximal gastric carcinomas.

Decreased expression of DCC mRNA in gastric and colorectal cancer

The deleted-in-colorectal-cancer (DCC) gene, located on chromosome 18q 21.3, is considered to be a tumor suppressor gene related to cellular adhesion receptors. A loss of heterozygosity (LOH) on chromosome 18q is frequently observed in adenomatous polyposis coli, as well as in sporadic colon carcinoma and its liver metastatic loci. In this study, we investigated the expression of DCC mRNA in the resected specimens of 38 gastric cancers and 28 colorectal cancers by a reverse transcription-polymerase chain reaction method. In the gastric cancer patients, the mean expression level of DCC mRNA in the tumors was significantly lower than that in normal tissues (p = 0.009), but no difference was observed in the colorectal cancer patients. DCC mRNA expression was decreased in 15 gastric cancers (40%) and 10 colorectal cancers (36%), and there was a significant correlation between the decreased expression of DCC mRNA and nodal metastasis in colorectal cancer (chi 2 = 7.049, DF = 1, P = 0.0079). Two of four gastric cancer patients and none of seven colorectal cancer patients whose cancers were confined to the muscularis propria without metastasis showed decreased expression of DCC mRNA. These findings demonstrate that decreased expression of DCC mRNA may occur at an early stage in gastric cancer and at a late stage in colorectal cancer and that this decreased expression correlates with the potential to develop nodal metastasis.

Allelic imbalance in gastric cancer: an affected site on chromosome arm 3p

In order to detect regions of DNA containing tumor suppressor genes involved in the development of gastric cancer, we performed an allelotype study on 78 gastric adenocarcinomas from a population composed largely of Texan Hispanics and Anglos, two ethnic groups that have a ratio of incidence rates of gastric cancer of approximately 2:1. In total, 42 microsatellite markers were employed, which detected at least one site per arm of each autosome in the human genome. These included several markers linked to known tumor suppressor genes (TP53, APC, DCC, RB1, and BRCA1). Sites showing quantitative allelic imbalance (AI) greater than 30% were located on 3p (36%), 11q (31%), 12q (38%), 13q (33%), 17p near TP53 (74%), and 17q near BRCAI (32%). Among the 22% of cases showing microsatellite instability (MI), a subset (4 of 17) showed instability at 59% or more of sites tested. No ethnic bias was detected in cases showing MI or in cases with AI at sites with rates of AI above 30%. Tumors of the intestinal subtype were significantly more likely than diffuse tumors to show AI at DI3S170 (P = 0.01). A deletion map of chromosome arm 3p was prepared for tumors with AI at D3S1478. These data indicate that a tumor suppressor gene on chromosome arm 3p is involved in the development of a subset of gastric cancers.

Abnormalities of the RB1 and DCC tumor suppressor genes: uncommon in human pancreatic adenocarcinoma

Evidence of RB1 allele loss was found in only 6% of pancreatic cancers, and we found no significant sequence abnormalities nor loss of RB protein expression in a panel of tumors and cell lines. Using reverse transcription-polymerase chain reaction and Southern blot analysis, we found no evidence for loss of DCC expression in pancreatic cancer cell lines, and allele loss only rarely in tumor biopsies. These findings suggest that abnormalities of RB1 and DCC are unlikely to play a major role in pancreatic carcinogenesis.

The molecular biology of esophageal and gastric cancer and their precursors: oncogenes, tumor suppressor genes, and growth factors

The evolution of sequential histological changes from normal cells through invasive cancer affords the cancer biologist the opportunity to identify separate molecular steps involved in cancer progression. As one studies the development of human carcinoma, it becomes apparent that multiple genetic alterations affecting both cellular proto-oncogenes and tumor suppressor genes are involved during the development and progression of both esophageal and gastric cancers. The different histological forms of both esophageal and gastric carcinomas as well as their differing etiologies result in the possibility that a spectrum of genetic changes is involved in different tumor types. p53 abnormalities occur frequently in tumors arising in both organs, and in both sites p53 abnormalities can be observed in precancerous lesions as well as in overt cancer. Subsequent abnormalities affecting other genes (eg, epithelial growth factor receptors [EGFRs]) potentially enhance the growth potential of tumors. This review focuses on abnormalities of oncogenes, tumor suppressor genes, and growth factors commonly found in cancers of the esophagus and stomach.

Point mutations of ras genes in human adrenal cortical tumors: absence in adrenocortical hyperplasia

Point mutations of ras genes (K-, H-, and N-ras) at codons 12, 13, and 61 and of the Gi2 alpha gene at codons 179 and 205, were studied in 56 primary adrenal cortical tumors and 6 adrenal cortical hyperplasias. Of 56 tumors, 24 were carcinomas and 32 were benign. The 24 carcinomas and 20 of the benign tumors were from American patients; the 12 remaining adenomas were from Japanese patients. Of the benign tumors 12 were cortisol-producing adenomas, 15 were aldosterone-producing adenomas, 3 were nonfunctioning adenomas, and 2 were adenomas that produced a virilizing syndrome. Tumor DNA obtained from archival formalin-fixed, paraffin-embedded tissue or fresh frozen tissue was amplified by polymerase chain reaction; and point mutations were detected by sequence-specific oligonucleotide hybridization. Activating ras mutations were found in 7 of 56 (12.5%) of all tumors: 3 of 24 (12.5%) carcinomas and 4 of 32 (12.5%) adenomas. Of adenomas from an American population, 4 of 20 (20%) exhibited positive ras mutations, whereas none was present in the Japanese tumors. All mutations detected were adenine to guanine transitions at the second position of N-ras codon 61, resulting in a conversion from glutamine to arginine. No mutations were found in K-ras or H-ras genes. Furthermore, no mutations of the Gi2 alpha gene were identified. These findings demonstrate that N-ras mutations at codon 61 may contribute to the genesis of both benign and malignant human adrenal cortical tumors. Finally, no mutations of the ras or Gi2 alpha genes were identified in hyperplastic adrenocortical tissues.

Deletion mapping reveals two regions of chromosome 8 allele loss in colorectal carcinomas

Colorectal carcinogenesis is associated with the accumulation of genetic changes involving both dominant oncogenes and tumor suppressor genes. Although at least four different genes have been implicated in the process, the detection of allele loss from other regions of the genome suggests the involvement of additional genes. The short arm of chromosome 8 is one of these regions; loss of heterozygosity occurs at rates ranging from 30 to 50%. To define the region of common deletion containing the putative tumor suppressor gene, we analyzed a series of 87 carcinomas for allele loss in different regions of the short arm of chromosome 8 by using Southern blot analysis and a panel of polymorphic probes. We found allele loss in 33% of our cases, which involves two separate regions, one in the p-terminal region of the chromosome, 8p23.1-pter, where 45% of informative cases demonstrated loss, and the other in the mid-p region, at 8p21, where 31% of cases showed allele loss. No tumors showed loss of heterozygosity for both regions. These findings suggest the presence of two discrete genes related to colorectal carcinogenesis on the short arm of chromosome 8.

Abnormalities affecting the APC and MCC tumour suppressor gene loci on chromosome 5q occur frequently in gastric cancer but not in pancreatic cancer

Abnormalities affecting tumour suppressor genes on chromosome 5q21 are increasingly recognised as important in the pathogenesis of a variety of human cancers, particularly of the gastrointestinal tract. We have examined a series of gastric and pancreatic cancers from European patients for loss of heterozygosity (LOH) of markers within and around the APC and MCC genes on chromosome 5q21 using restriction fragment length polymorphism and polymerase chain reaction techniques. We find that LOH of the APC and MCC genes is particularly frequent in gastric cancers of diffuse type, but very infrequent in pancreatic cancers. We have also used single-strand conformational polymorphism to screen for abnormalities of the sequence of the APC and MCC genes in a panel of pancreatic cancer cell lines. Our results suggest that there are distinct differences in the molecular pathogenesis of gastric and pancreatic cancer and that abnormalities of APC and MCC may be involved particularly in the diffuse type of gastric cancer.

Loss of heterozygosity and K-ras gene mutations in gastric cancer

In order to identify relevant genetic lesions in gastric carcinoma, we searched for tumor suppressor gene inactivation and K-ras gene mutations by analyzing tumor and control DNAs from 34 patients. These were from an epidemiologically defined area of Italy characterized by one of the world's highest incidences of stomach cancer. Allele losses were investigated by the Southern blotting procedure at 16 polymorphic loci on 11 different chromosomes. Our data demonstrate that chromosomal regions 5q, 11p, 17p and 18q are frequently deleted, and that 7q and 13q chromosome arms are also involved, although at a lower frequency. Loss of heterozygosity (LOH) at region 11p was not found during other surveys carried out on patients of different geographic origins. No specific combination of allelic losses could be recognized in the samples analyzed, the only exception being that tumors with 17p allelic loss also showed LOH on the 18q region. When matching frequent LOH events and the stage of progression of the tumors, we observed a trend of association between advanced stages and allelic losses on 17p and 18q chromosome arms. The analysis of K-ras, carried out by the polymerase chain reaction and denaturing gradient gel electrophoresis, demonstrated transforming mutations in only 3 out of 32 cases. Colorectal tumorigenesis proceeds by the accumulation of genetic alterations, including K-ras mutations and inactivation of tumor suppressor genes on the 5q, 17p and 18q regions. Our data indicate that, although gastric and colorectal neoplasias share common genetic alterations, they probably progress through different pathways.

Karyotypic abnormalities in tumours of the pancreas

Short-term cultures from 20 pancreatic tumours, three endocrine and 17 exocrine, were cytogenetically analysed. All three endocrine tumours had a normal chromosome complement. Clonal chromosome aberrations were detected in 13 of the 17 exocrine tumours: simple karyotypic changes were found in five carcinomas and numerous numerical and/or structural changes in eight. When the present findings and those previously reported by our group were viewed in conjunction, the most common numerical imbalances among the 22 karyotypically abnormal pancreatic carcinomas thus available for evaluation turned out to be, in order of falling frequency, -18, -Y, +20, +7, +11 and -12. Imbalances brought about by structural changes most frequently affected chromosomes 1 (losses in 1p but especially gains of 1q), 8 (in particular 8q gains but also 8p losses), and 17 (mostly 17q gain but also loss of 17p). Chromosomal bands 1p32, 1q10, 6q21, 7p22, 8p21, 8q11, 14p11, 15q10-11, and 17q11 were the most common breakpoint sites affected by the structural rearrangements. Abnormal karyotypes were detected more frequently in poorly differentiated and anaplastic carcinomas than in moderately and well differentiated tumours.