Gene amplification and proliferative kinetics in relation to prognosis of patients with gastric carcinoma

Cytogenetic and molecular aspects of gastric cancer: clinical implications

Gastric cancer is of major importance world-wide being the second most common cause of cancer-related death in the world. According to Lauren's histological classification gastric cancer is divided in two groups, the better differentiated intestinal carcinomas and the poorly differentiated diffuse-type cancers. The genetic changes underlying the initiation and progression of gastric cancer are not well defined. Gastric carcinogenesis is a multistep process involving a number of genetic and epigenetic factors. Although it has been proposed that different genetic pathways exist for differentiated and undifferentiated carcinomas, the two histological subtypes of gastric cancer share some common genetic alterations. Currently, tumor histology and pathologic stage are the major prognostic variables used in the clinical practice for gastric cancer patients. However, it is known that tumors with similar morphology may differ in biological aggressiveness, prognosis and response to treatment. Molecular genetic analysis of gastric cancer revealed a number of associations of certain genetic changes with pathological features, tumor biological behavior and prognosis of gastric cancer patients, suggesting that these genetic abnormalities might play an important role in gastric tumorigenesis. Increasing evidence suggests that the molecular genetic changes could be helpful in the clinical setting, contributing to prognosis and management of patients. Regarding epigenetic events in gastric tumorigenesis, a number of methylating markers have been proposed for risk assessment, prognostic evaluation and as therapeutic targets. However, further research is required in order to systematically investigate the genetic changes in gastric cancer estimating also their usefulness in the clinical practice. A good understanding of the genetic changes underlying gastric carcinogenesis may provide new perspectives for prognosis and screening of high risk individuals. Some of the genetic alterations could definitely improve tumor classification and management of gastric cancer patients. Also, based on molecular data identified in gastric cancer novel therapeutics might help to improve the treatment of this disease.

Non-incidental coamplification of Myc and ERBB2, and Myc and EGFR, in gastric adenocarcinomas

This study was conducted to assess the frequencies of protein overexpression and gene amplification of Myc and to identify the mechanisms of Myc gene amplification, especially with regards to its possible coamplification with ERBB2 or EGFR in gastric adenocarcinomas. By immunohistochemical analysis of a total of 300 formalin-fixed and paraffin-embedded gastric adenocarcinomas, the nuclear overexpression of MYC was found in 47 tumors (16%). A fluorescence in situ hybridization (FISH) analysis revealed that nine (19%) of the 47 tumors with protein overexpression had cancer cells with high levels of Myc amplification, whereas only seven (6%) of the 122 tumors without protein overexpression showed high-level Myc gene amplification. Such Myc amplification was significantly correlated with positive nuclear protein overexpression. The coamplification of ERBB2 or EGFR with Myc that was found in six and four cases, respectively, is believed to be non-incidental because those frequencies were significantly higher than the individual frequencies observed for the total examined cases (ERBB2: 7%; EGFR: 4%). The high levels of gene amplification of these three genes, as visualized by FISH, could be broadly classified into two typical types, namely, 'multiple scattered signals' and 'large clustered signals'. Using two-color FISH, the coexistence of coamplified Myc and ERBB2, or Myc and EGFR, within single nuclei in various combinations of amplification types and copy numbers, could be ascertained in all nine cases, including one in which the synchronous 'multiple scattered type' coamplification of Myc and ERBB2 was observed. In three tumors, coamplification of ERBB2 and EGFR was found; however, ERBB2- and EGFR-amplified cell populations were separate and mutually exclusive. We propose that the non-incidental coamplification of Myc and either ERBB2 or EGFR occurred through translocation and subsequent rearrangement.

Interrelationship between chromosome 8 aneuploidy, C-MYC amplification and increased expression in individuals from northern Brazil with gastric adenocarcinoma

AIM: To investigate chromosome 8 numerical aberrations, C-MYC oncogene alterations and its expression in gastric cancer and to correlate these findings with histopathological characteristics of gastric tumors.

METHODS: Specimens were collected surgically from seven patients with gastric adenocarcinomas. Immunostaining for C-MYC and dual-color fluorescence in situ hybridization (FISH) for C-MYC gene and chromosome 8 centromere were performed.

RESULTS: All the cases showed chromosome 8 aneuploidy and C-MYC amplification, in both the diffuse and intestinal histopathological types of Lauren. No significant difference (P < 0.05) was observed between the level of chromosome 8 ploidy and the site, stage or histological type of the adenocarcinomas. C-MYC high amplification, like homogeneously stained regions (HSRs) and double minutes (DMs), was observed only in the intestinal-type. Structural rearrangement of C-MYC, like translocation, was observed only in the diffuse type. Regarding C-MYC gene, a significant difference (P < 0.05) was observed between the two histological types. The C-MYC protein was expressed in all the studied cases. In the intestinal-type the C-MYC immunoreactivity was localized only in the nucleus and in the diffuse type in the nucleus and cytoplasm.

CONCLUSION: Distinct patterns of alterations between intestinal and diffuse types of gastric tumors support the hypothesis that these types follow different genetic pathways.

Cyclooxygenase-2 and c-erbB-2 expression in colorectal carcinoma assessed using tissue microarrays

The c-erbB-2 and cyclooxygenase (COX) pathways are involved in the pathogenesis of colorectal carcinoma, but the relationship is not fully understood. This study evaluated the significance of c-erbB-2, COX-2, and Ki-67 protein expression in 185 patients with colorectal carcinoma using tissue microarrays. Only one case expressed cerbB-2 protein. COX-2 expression was noted in 166 of 176 cases (94.3%), and the Ki-67 expression rate averaged 5.9%. There was no relationship among c-erbB-2, COX-2, and Ki-67 protein expression, and COX-2 protein expression was not related to tumor stage, differentiation, size, depth of invasion, lymphatic or vascular invasion, or patient survival. While the contribution of c-erbB-2 to colorectal carcinogenesis may be of little quantity, COX-2 may be deeply involved in colorectal carcinogenesis.

c-erb B-2 expression is associated with tumor location and venous invasion and influences survival of patients with gastric carcinoma

The HER-2/neu gene or c-erb B-2, localized on chromosome 17q, belongs to a family of tyrosine kinase receptors and shares extensive homology with the epidermal growth factor receptor. c-erb B-2 gene amplification and protein overexpression have been reported in several human cancers. The prognostic value of this genetic alteration in gastric carcinoma is far from being established. In the present study, formalin-fixed, paraffin-embedded gastric carcinoma tissues from 157 patients were evaluated for c-erb B-2 overexpression, by immunohistochemistry using a polyclonal antibody. c-erb B-2 expression was evaluated according to clinical and pathological parameters, and to the survival of the patients. Our results show that: (1). c-erb B-2 was overexpressed in 15.3% of gastric carcinoma cases; (2). c-erb B-2 overexpression was significantly more frequent in cardia (23.8%) and fundus/body (25.0%) carcinomas than in antrum (7.2%) carcinomas; (3). c-erb B-2 overexpression was significantly associated with venous invasion; (4). c-erb B-2 is a prognostic factor for gastric carcinoma.

c-erbB-2 is not a major factor in the development of colorectal cancer

We have investigated c-erbB-2 protein expression in a large cohort of well-characterized colorectal tumours, and in a subset of lymph node metastases. We have also evaluated a Val(655)Ile single nucleotide polymorphism, which is associated with an increased risk of breast cancer, in a subset of the colorectal cancer patients and in healthy control subjects. Immunohistochemical studies revealed that while 81.8% of tumours expressed c-erbB-2, in the majority of cases equivalent levels of c-erb-B2 were seen in adjacent normal mucosa. Colon tumours were significantly more likely to express c-erbB-2 than rectal tumours (P=0.015). Only 52.4% of the metastases displayed staining patterns concordant with their primary tumour, indicating that determination of c-erbB-2 protein in colorectal tumours cannot predict the status of lymph node metastases. PCR--RFLP analysis of the Val(655)Ile single nucleotide polymorphism demonstrated that allele frequencies were identical between colorectal cancer patients and a control group of Caucasian subjects (Ile=0.80 and Val=0.20 in each case), indicating that it is not related to the risk of developing colorectal cancer in this population. Furthermore, there was no relationship between c-erbB-2 protein expression and gene polymorphism (P=0.58). In terms of prognosis, no association was seen between either c-erbB-2 protein expression or the presence of the Val allele and patient survival (P>0.05 in each case), suggesting that c-erbB-2 is not a prognostic marker in colorectal cancer.

Examination of oncogene amplification by genomic DNA microarray in hepatocellular carcinomas: comparison with comparative genomic hybridization analysis

To identify amplified oncogenes involved in hepatocellular carcinomas (HCC), we applied a genomic DNA microarray spotted with 57 oncogenes to 20 HCCs. Aberrations in DNA copy number also were analyzed by comparative genomic hybridization (CGH) using an aliquot of DNA samples. In 5 of 20 HCCs, only 6 oncogenes (CCND1, FGF3/FGF4, SAS/CDK4, TERC, MET, and MYC) were amplified, whereas in the remaining 15 tumors no oncogenes were amplified. A comparison of DNA microarray and conventional CGH analyses showed that, although 5 of 6 amplified oncogenes shown by microarray were located in chromosomal regions shown by CGH to have increased DNA copy numbers, not all genes located in such chromosomal regions were affected. One of the amplified oncogenes (SAS/CDK4) was found in a chromosomal region that was undetected by CGH. We, therefore, conclude that amplification of the oncogenes examined in this series is not directly implicated in hepatocellular carcinogenesis.

DNA amplification and chromosomal translocations are accompanied by chromosomal instability: analysis of seven human colon cancer cell lines by comparative genomic hybridization and spectral karyotyping

Genetic instability in human cancers is classified as chromosomal instability (CIN) or microsatellite instability (MIN). DNA amplification and translocations are observed frequently in various cancers. We used comparative genomic hybridization (CGH) and spectral karyotyping (SKY) to study seven human colon cancer cell lines and investigate the relations among genetic instability, DNA amplification, and chromosomal translocations. DNA amplification was found in five cell lines (COLO320DM, COLO201, WiDr, CoCM-1, and CACO-2), and all were aneuploid. In these five cell lines, segments of chromosomes were translocated to other chromosomes. In contrast, cell lines with MIN, DLD-1, and LoVo did not show DNA amplification. The LoVo cells with MIN were considered near diploid and contained translocations. These findings suggest that DNA amplification and chromosomal translocations are accompanied by CIN.

Diagnostic and prognostic tumor markers in the gastrointestinal tract

The gastrointestinal tract is the most common site of malignancies of any anatomic system in the body. An early detection of primary tumors of the bowel, pancreas, liver, stomach, and esophagus is often difficult in asymptomatic patients and for this reason these tumors are often detected at a relatively advanced stage, when symptoms lead to a diagnostic evaluation. Furthermore, gastrointestinal tract tumors have an extremely variable prognosis; thus, the identification of new prognostic parameters may be useful for selecting patients to more tailored therapies. In this work, the main molecular, genetic, tissular, and circulating tumor markers proposed for diagnosis and prognosis of gastrointestinal malignancies are reviewed and discussed.

Correlation of histologic subtypes and replication error phenotype with comparative genomic hybridization in gastric cancer

To characterize phenotypic and genotypic changes in gastric cancer (GC), DNA copy number aberrations (CNAs) were assessed in 53 tumors using comparative genomic hybridization (CGH) and correlated with clinicopathologic characteristics and status of TP53 and replication error (RER). The number of CNAs per tumor was 6.8 (gain 5.3, loss 1.5), and the number of changes was significantly higher in tumors with advanced stage, TP53 mutation, and without RER than in those with early stage (7.7 vs. 3.0), no TP53 mutations (12.4 vs. 4.8) or RER phenotype (8.2 vs. 2.6). Frequent abnormalities included gains on chromosomal arms 8q (43%), 6q (26%), 11q (26%), 13q (24%), 7p (23%), 17q (23%), and 20q (23%), and losses on chromosomal arms 16q (26%), 19p (23%), 5q (19%), 3p (15%), 4q(15%), and 1p (15%). Advanced GC demonstrated a higher prevalence of gains of 8q (51% vs. 10%, P < 0.05) and loss of 16q (33% vs. 0%, P < 0.05) than early GC. Gains on 8q (64% vs. 20%, P < 0.05), 17q (39% vs. 4%, P < 0.05) and losses on 3p (25% vs. 4%, P = 0.05) and 5q (32% vs. 4%, P < 0.05) were higher in intestinal GC than in diffuse GC. On the other hand, gains on 13q were more common in the diffuse type (40% vs. 11%, P < 0.05). As compared with noncardia cancer, cardia cancer showed more gains on 7p (58% vs. 12%, P < 0.05) and 20q (58% vs. 12%, P < 0.05) and more losses on 4q (50% vs. 5%, P < 0.05). The finding of histology-related aberrations and the combination of CGH and molecular data thus provide additional evidence suggesting genetic heterogeneity of GC.

Nuclear profiles of cancer cells reveal the metastatic potential of gastric cancer

Nuclear profiles have been reported as useful prognostic predictors in various cancers. Data from computerized morphometry are objective and can be quickly derived using conventional microscopic analysis, but image analysis of nuclear features has only rarely been applied to investigations of gastric cancer. The aim of this study was to evaluate the correlation between one of these morphological nuclear features and the clinicopathological parameters in patients with gastric cancer. The morphometric nuclear feature (nuclear area) was analysed in 400 patients with gastric cancer. In each case, 300 cancer nuclei on routine haematoxylin and eosin-stained slides were analysed through the use of a computer-assisted image analysis system which traced the nuclear profiles (magnificationx400) on a computer monitor. The morphometric data were compared with the patients' clinicopathological status and survival rate. The mean nuclear area (NA) of cancer cells from 400 cases of gastric cancer was 47.2 microm(2). The NAs of cancer cells from tumours with microvessel invasion (lymphatic or venous invasion), lymph node metastasis or hepatic metastasis at the time of operation were significantly larger than those of cancer cells from tumours without such invasion or metastases. Cytokeratin (CK) immunostaining was performed on 2577 lymph nodes from 91 patients with advanced gastric cancer (pT3, pN0, pM0, stage II) to detect micrometastases. CK-positive lymph nodes were detected in 350 of 2577 lymph nodes (13. 6%) and in 62 of 91 patients (68.1%). The mean NA of cancer cells from 62 tumours with micrometastases (44 microm(2)) was larger than that of cancer cells from 29 tumours without micrometastases (38.8 microm(2), p=0.043), and a significant positive correlation was detected between the NAs of cancer cells from 91 tumours and the number of micrometastatic lymph nodes of 91 patients (rho=0.278, p=0. 008). Cancer cells with large NA correlated strongly with haematogenous and lymph node recurrence or relapse after gastrectomy and the NA of cancer cells was identified as an independent prognostic factor in gastric cancer. Nuclear morphometry is an objective, reproducible, and technically uncomplicated procedure. The NA of cancer cells correlates closely with the metastatic potential of gastric cancer. Nuclear morphometry may therefore be useful for the selection of patients who are at risk of haematogenous or lymph node metastatic recurrence after surgery.

Detection of gene amplification in archival breast cancer specimens by laser-assisted microdissection and quantitative real-time polymerase chain reaction

Gene amplification is one of the most important mechanisms leading to deregulated gene expression in cancer. The exact quantitative detection of this frequent genomic alteration in solid tumors is often hampered by an admixture of nonneoplastic bystander and stroma cells. To overcome this obstacle and to develop an objective quantitative method we have combined laser-assisted microdissection of tumor cells with the novel 5'-exonuclease-based real-time polymerase chain reaction (PCR) assay. The latter method enables the highly reproducible exact quantification of minute amounts of nucleic acids. As a model system amplification of c-erbB2/Her-2/neu gene and the adjacent topoisomerase IIalpha gene was determined in paraffin-embedded breast cancer specimens (n = 23) after immunohistochemical labeling and laser-based microdissection of tumor cells. The high sensitivity of real-time PCR enabled the reliable and objective detection of low-level amplifications in as few as 50 cells from archival tissue sections. Low-level amplifications were shown to escape from detection unless tumor cells were isolated by microdissection. In selected cases intratumor heterogeneity was demonstrated using areas of approximately 50 to 100 cells. This novel approach combining immunohistochemistry, laser microdissection, and quantitative kinetic PCR allows morphology-guided studies in archival tissue specimens and will enable the exact quantification of gene copy numbers in even small and precancerous lesions.

Rare mutations of p53, Ki-ras, and beta-catenin genes and absence of K-sam and c-erbB-2 amplification in N-methyl-N'-nitro-N-nitrosoguanidine-induced rat stomach cancers

Rat stomach cancers induced by N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) have been widely used as a model for human stomach cancers of the differentiated type. However, there has been little information regarding their molecular basis. In this study, we examined the genetic alterations reported in human stomach cancers in 10 rat stomach cancers that had been induced in male ACI/N rats by administering MNNG in the drinking water. One of the 10 cancers had a mutation of the p53 gene at the second position of codon 171 (Val --> Glu). However, none of the 10 cancers had mutations in codons 12, 13, or 61 of Ki-ras or in the N-terminal phosphorylation sites of the beta-catenin gene. Southern blot analysis showed no amplification of K-sam or c-erbB-2 in the seven cancers examined. Finally, we searched for microsatellite alterations in 12 loci in nine cancers, but no alterations were observed. As these genetic alterations are observed in only a minor fraction of human stomach cancers, further analysis of genetic and epigenetic alterations in MNNG-induced rat stomach cancers is needed to disclose the major mechanisms of stomach carcinogenesis.

Significance of cell proliferation measurement in gastric cancer

Cell kinetic data may be important indicators of clinical behaviour in many types of cancer. Recently, several antibodies to cell-cycle associated antigens have been characterised. This overview summarises the advantages and disadvantages of different methods for the assessment of cell proliferation. Moreover, the prognostic value of proliferative activity in gastric cancer is discussed and suggestions for future research are given.