Clonal analysis of colorectal tumors using K-ras and p53 gene mutations as markers

Hit-And-Run Mechanism of HBV-Mediated Progression to Hepatocellular Carcinoma

Aim and background

Hepatitis B virus is implicated in the development of hepatocellular caracinoma. No oncogenes have been identified within the viral genome. Furthermore, it frequently fragments after integration into the hepatocyte genome. Simultaneous investigations of hepatitis B virus integration patterns and genetic changes in precancerous tissues are important to understand the role played by hepatitis B virus integration in hepatocellular caracinoma.

Method

We used a combination approach of dual characterization of highly polymorphic loci and the change in hepatitis B virus-DNA integration pattern. Large regenerative nodules were dissected from 6 explanted hepatitis B virus infected cirrhotic livers. Nodules within each liver segment were schematically mapped and histopathologically analyzed. Genomic DNA from each nodule was analyzed for hepatitis B virus integration and the genetic stability of 12 microsatellite loci including D3S2321, D8S1022, D17S1159, D4S2281, D5S1/2, D16S675, D16S685, D16S490, D16S526, D16S673, D16S677 and D16S690.

Results

Data from different liver segments revealed few viral integrations and average allele loss. The most exciting results came from a segment containing a set of clonally and spatially related nodules having similar histologic features, a progressive lineage of allele loss, HBV integration and loss of integration.

Conclusions

This model portrait, a scenario of genetic events that precede tumor formation where the acquisition and loss of hepatitis B virus integrations in clonally related regenerative nodules, might explain how the virus acts as a hit-and-run mutagen.

Comparative genomic analysis of primary and synchronous metastatic colorectal cancers

Approximately 50% of patients with primary colorectal carcinoma develop liver metastases. Understanding the genetic differences between primary colon cancer and their metastases to the liver is essential for devising a better therapeutic approach for this disease. We performed whole exome sequencing and copy number analysis for 15 triplets, each comprising normal colorectal tissue, primary colorectal carcinoma, and its synchronous matched liver metastasis. We analyzed the similarities and differences between primary colorectal carcinoma and matched liver metastases in regards to somatic mutations and somatic copy number alterationss. The genomic profiling demonstrated mutations in APC(73%), KRAS (33%), ARID1A and PIK3CA (6.7%) genes between primary colorectal and metastatic liver tumors. TP53 mutation was observed in 47% of the primary samples and 67% in liver metastatic samples. The grouped pairs, in hierarchical clustering showed similar somatic copy number alteration patterns, in contrast to the ungrouped pairs. Many mutations (including those of known key cancer driver genes) were shared in the grouped pairs. The ungrouped pairs exhibited distinct mutation patterns with no shared mutations in key driver genes. Four ungrouped liver metastasis samples had mutations in DNA mismatch repair genes along with hypermutations and a substantial number of copy number alterations. Our results suggest that about half of the metastatic colorectal carcinoma had the same clonal origin with their primary colorectal carcinomas, whereas remaining cases were genetically distinct from their primary carcinomas. These findings underscore the need to evaluate metastatic lesions separately for optimized therapy, rather than to extrapolate from primary tumor data.

Heterogeneous distribution of K-ras mutations in primary colon carcinomas: implications for EGFR-directed therapy

PURPOSE

K-ras mutations predict resistance against epidermal growth factor receptor (EGFR)-directed therapy of metastatic colorectal cancer (CRC). The purpose of this study was to analyze the distribution of K-ras mutations in primary tumors and corresponding sentinel lymph nodes (SLNs) from colon cancer patients.

METHODS

Tumor biopsies and SLNs from 158 patients with non-metastatic colon cancer were analyzed for K-ras mutations in codons 12 and 13 by a sensitive and quantitative peptide nucleic acid clamp PCR assay.

RESULTS

Analyses of single fresh-frozen tumor biopsies revealed K-ras mutations in 67 (42%) of the patients. Apparently low levels of K-ras mutations in 13 of the mutated primary tumors and the presence of K-ras mutations in SLNs from seven patients with a wild-type primary tumor biopsy suggested possible intratumoral heterogeneity for 20 of the patients. To confirm this hypothesis, we analyzed tissue sections from all available formalin-fixed, paraffin-embedded (FFPE) tumor blocks from these 20 patients. Ten of the patients had a mixture of tissue sections positive and tissue sections negative for K-ras mutations, two patients had K-ras mutations in all sections, and eight patients had no detectable K-ras mutations in tumor FFPE tissue blocks. Among these eight patients, five had K-ras mutations detected in SLNs. Thus, evidence supporting a heterogeneous distribution of K-ras mutations was obtained for 15 patients.

CONCLUSIONS

Heterogeneous distribution of K-ras codon 12 and 13 mutations within primary tumor, or between primary tumor and lymph node metastases, was demonstrated for 15 (20%) of 74 colon cancer patients having K-ras mutations. This may have implications for tissue sampling routines with regard to EGFR-directed therapy of CRC, both in adjuvant and metastatic settings.

TP53 mutations in human cancers: origins, consequences, and clinical use

Somatic mutations in the TP53 gene are one of the most frequent alterations in human cancers, and germline mutations are the underlying cause of Li-Fraumeni syndrome, which predisposes to a wide spectrum of early-onset cancers. Most mutations are single-base substitutions distributed throughout the coding sequence. Their diverse types and positions may inform on the nature of mutagenic mechanisms involved in cancer etiology. TP53 mutations are also potential prognostic and predictive markers, as well as targets for pharmacological intervention. All mutations found in human cancers are compiled in the IARC TP53 Database (http://www-p53.iarc.fr/). A human TP53 knockin mouse model (Hupki mouse) provides an experimental model to study mutagenesis in the context of a human TP53 sequence. Here, we summarize current knowledge on TP53 gene variations observed in human cancers and populations, and current clinical applications derived from this knowledge.

Rapid induction of malignant tumor in Sprague–Dawley rats by injection of RK3E-ras cells

Several tumor animal models have been provided as a tool for developing cancer therapy. Here, we developed rapid, easy-to use, and cost-effective new rat animal model for invasion and metastasis of cancer using genetically k-ras-induced rat kidney cells (RK3E-ras). We observed tumor as early as 3 days after injection of RK3E-ras cells in subcutaneous of Sprague-Dawley rats. Tumor size and volume were increased exponentially for 2 weeks. The tail vein injected rats obtained the lethal infiltration in the lung within 2 weeks. This tumor animal model has great potential for studying cancer processes and short-term screening of variable cancer therapy strategy.

Peptide nucleic acid clamp PCR: a novel K-ras mutation detection assay for colorectal cancer micrometastases in lymph nodes

Inaccurate staging of colorectal cancer (CRC) has been attributed to the failure to detect lymph node metastases by conventional pathology. We have previously reported the use of lymphatic mapping to accurately identify those lymph nodes most likely to harbor micrometastatic disease and permit focused pathologic examination. Mutation of K-ras allele at codons 12 or 13 occurs frequently in early stages of CRC development. The purpose of our study was to assess sentinel lymph nodes (SLN) for occult CRC micrometastases using a unique peptide nucleic acid (PNA) clamp PCR assay specific for K-ras mutations. Seventy-two paraffin-embedded primary CRC and paired SLN were evaluated by PNA clamp PCR for K-ras mutations. Thirty primary tumors (42%) were positive for K-ras mutations, and in 5 of these cases the SLN were positive for metastases by Hematoxylin and Eosin staining. PNA clamp PCR identified occult metastases in an additional 6 patients, upstaging 24% of K-ras positive primary CRCs (p = 0.014). No K-ras mutations were detected among the 20 noncancer lymph nodes assessed. This study demonstrates the utility, specificity and sensitivity of PNA clamp PCR assay in identifying occult micrometastases in the SLN of CRC patients by single-base mutation analysis.

Accuracy of two-dimensional electrophoresis for target discovery in human colorectal cancer

Two-dimensional polyacrylamide gel electrophoresis (2-D PAGE) is increasingly used for target discovery in human disease to complement genomic studies. We have assessed the possibilities and limits of 2-D PAGE applied to human colorectal cancer. Up to 10(8) epithelial cells were purified from paired normal and pathological biopsies using Ber-EP4 coated magnetic beads, allowing the elimination of cellular and fluid contaminations. The mean coefficient of variation (CVAR) of repeated 2-D PAGE analysis with silver staining was lying between 20 and 28%. However, only 47% (interrun) to 76% (intrarun) of spots could be matched within a triplicate experiment. Interindividual phenotypic variability was high. Intratumoral phenotypic variability was not found to be significant. When method and tumor variability were added, 90% of CVAR were inferior to 48%. Thus, two-fold up- or down-regulation of protein expression reveals biological significance. Serial paired comparison of 923 proteins in 10 patients showed highly reproducible differences between normal and cancer tissues. Under well defined experimental conditions and after the high variability of the technique has been considered, 2-D PAGE parallel analysis of paired colorectal samples allows patient-specific tumor profiling.

K-ras Mutational Analysis of Polyclonal Colorectal Cancers Identifies Uniclonal Circulating Tumor Cells

The clonal development of colorectal carcinoma resulting from specific mutations in certain oncogenes and/or tumor suppressor genes is a well-accepted model. It is increasingly recognized that a majority of colorectal cancers are polyclonal on the basis of molecular analysis that demonstrates cells with different mutations within a given oncogene or tumor suppressor gene in the same tumor. This polyclonal pattern may occur as a result of either clonal convergence or divergence during the many steps of oncogenesis. Further complicating this picture is the fact that metastatic lesions may arise from only one of the clonal populations within a tumor and thereby present only a partial molecular make-up of the whole tumor. There are few data available that define clonal selection or specificity of circulating tumor cells in patients undergoing curative resection of colorectal carcinoma. The purpose of this paper is to describe the clonal distribution of circulating tumor cells in four patients with multiple K- ras mutations present in the primary lesion. Patients were selected who were known to have polyclonal primary colorectal cancers resected for cure. All patients had multiple mutations present in exon one, codon 12 and/or 13, of the K- ras gene. Blood samples were drawn immediately before surgery and at 2-week to 6-month intervals postoperatively. Epithelial cells were isolated from peripheral blood mononuclear cells using Dynal ImmunobeadsRT coated with antiepithelial antibodies. DNA was extracted from these cells and analyzed for all K- ras mutations present in codons 12 and 13 of the patient's primary tumor using allele-specific polymerase chain reaction followed by Microwell Array Diagonal Gel Electrophoresis. Circulating tumor cells were identified in all four patients. However, in each case of positive circulating cells the only mutation identified was an aspartic acid mutation at codon 13. Once positive the circulating tumor cells persisted in subsequent multiple blood samples. These results provide further strength for the theory of polyclonal progression in primary colorectal cancers, although there may be specific mutational patterns that confer the ability to metastasize. The significance of this persistence of the glycine-to-aspartic acid mutation at codon 13 remains to be defined given that none of these patients has clinical evidence of recurrent cancer at the time of this report.

Discordance between K-ras mutations in bone marrow micrometastases and the primary tumor in colorectal cancer

PURPOSE

To study bone marrow micrometastases from colorectal cancer patients for the presence of K-ras mutations and to compare their genotype with that of the corresponding primary tumor.

PATIENTS AND METHODS

Bilateral iliac crest aspiration was performed in 51 patients undergoing surgery for colorectal cancer, and bone marrow micrometastases were detected by immunohistochemistry. The presence of K-ras mutations was determined by single-strand conformation polymorphism analysis on both primary tumors and paired bone marrow samples and was confirmed by sequencing.

RESULTS

In six patients with primary tumor mutations, it was possible to amplify a mutated K-ras gene also from the bone marrow sample. In three of those patients the pattern of K-ras mutations differed between both samples, in two patients the mutation was identical between the bone marrow and its primary tumor, and in one patient the same mutation plus a different one were found. Fifteen of 17 K-ras mutations found in primary tumors were located in codon 12, whereas in bone marrow, five of seven mutations were found in codon 13 (P =.003).

CONCLUSION

Our results demonstrate that, at least for K-ras mutations, disseminated epithelial cells are not always clonal with the primary tumor and they question the malignant genotype of bone marrow micrometastases. They also indicate that different tumoral clones may be circulating simultaneously or sequentially in the same patient. Analysis of the type of mutations suggests that cell dissemination might be an early event in colorectal carcinogenesis.

Heterogeneity of p53 mutational status in intramucosal carcinoma of the colorectum

The aim of this study was to elucidate whether or not p53 genetic heterogeneity would occur while colorectal carcinoma was limited to the mucosa. Eight cases of endoscopically resected colorectal intramucosal carcinomas were analyzed to determine the p53 gene sequence (exons 5 to 8). Six out of 8 cases showed p53 gene mutations, and in all of them, the mutational status was heterogeneous. In 4 cases, mutated codons were heterogeneous as well. These data indicate that p53 gene alterations in colorectal carcinomas occur and diverge at the stage of intramucosal carcinoma, supporting our previously proposed hypothesis that colorectal carcinomas can be composed of various subclones as regards p53 gene mutation, while the carcinoma is limited to the mucosa, and one of these subclones commences invasion to the submucosa after clonal selection, thus generating a monoclonal invasive carcinoma.

In situ detection of specific p53 mutations in cultured cells using the amplification refractory mutation system polymerase chain reaction

Accurate molecular detection of genetic mutations involved in tumorigenesis has been based predominantly on analysis of extracted DNA, but this does not provide detailed information on the location, number, type or clonal distribution of mutated cells and their precise anatomic location and clonal distribution. This study has used a sensitive and specific application of the amplification refractory mutation system (ARMS)-polymerase chain reaction (PCR) in situ, combined with in situ hybridization to localize and identify cells with defined p53 mutations. The ARMS-PCR was performed in situ in SW480 cells in suspension and in cells either cultured or cytospun onto glass slides. Amplified mutant DNA PCR products were detected in SW480 cells using digoxigenin-labeled probes, visually identifying cells harboring specific mutations in the p53 gene. In situ hybridization alone of the mutant cells without the amplification step was negative. Normal human fibroblasts or endothelial cells were refractory to in situ amplification. This reaction was mutation-specific as CEM cells with different p53 mutations reacted negatively. Mutant messenger RNA (mRNA) in tumor cells was also selectively amplified in situ by ARMS-PCR following reverse transcription (RT). This study demonstrates the potential of in situ ARMS-PCR or RT-ARMS-PCR for mutation analysis in situ and could have useful clinical applications.

Can p53 alterations be used to predict tumour response to pre-operative chemo-radiotherapy in locally advanced rectal cancer?

PURPOSE

To examine whether p53 tumour suppressor gene alterations can be used to predict tumour response to pre-operative chemo-radiation in locally advanced rectal cancer in terms of reduction in tumour size and local failure.

METHODS

p53 alterations were studied in pre-treatment biopsy specimens of rectal carcinomas from 48 patients by immunohistochemistry (IHC) and polymerase chain reaction/single strand conformation polymorphism (PCR-SSCP) gene mutation analysis. Pre-operative pelvic radiotherapy was delivered with four fields, 45 Gy to the ICRU point in 25 fractions over 5 weeks. A radio-sensitising dose of 5-fluorouracil (500 mg/m(2)) was delivered concurrently for 6 days of the 5-week schedule (days 1, 2, 3 and days 22, 23 and 24). Total meso-rectal excision was planned 4 to 6 weeks from completion of pre-operative treatment. Response to therapy was assessed by macroscopic measurement of the surgical specimen by a pathologist who was unaware of the pre-treatment tumour size or of the p53 status.

RESULTS

IHC evidence of p53 protein accumulation was found in 40% of tumours, p53 gene mutation in 35% and p53 alteration (either or both changes) in 46%. The average reduction in tumour size was 53% in the group with 'wild-type' p53 (IHC-/SSCP-) and 63% in the group with altered p53 (either IHC+ or SSCP+; P=0.18). No significant differences in tumour size reduction or local failure were observed in the groups with p53 overexpression or p53 mutation compared with normal.

CONCLUSIONS

p53 alteration detected by IHC or SSCP analysis is not a clinically useful predictor of local response to pre-operative adjuvant therapy in advanced rectal carcinoma.

Keratin 20 is a specific marker of submicroscopic lymph node metastases in colorectal cancer: validation by K-RAS mutations

Lymph node status has major prognostic importance in colorectal cancer and greater precision in the diagnosis of lymph node metastases should provide better prognostic and therapeutic guidance. Keratin 20 (K20) gene expression has been used as a marker of lymph node metastases, but the evidence for this remains circumstantial. This study has therefore sought to determine K20 specificity and to correlate K20 expression with mutant K-RAS expression, in order to provide direct evidence that K20 expression in lymph nodes of colorectal cancer patients genuinely reflects metastatic disease. Specificity of K20 expression was established against a range of tissue types and 289 lymph nodes from 41 non-cancer control patients. K20 expression was restricted to gastrointestinal epithelia and was only present in one of the 289 control lymph nodes, giving a calculated specificity of 97.6% (95% confidence limits: 87.1-99.9%). Forty-two tumour samples were analysed for the presence of K-RAS codon 12 gene mutations using a RT-PCR mutant allele-specific amplification (MASA) technique. Thirteen tumours (31%) had codon 12 mutations detected by MASA and these were further analysed to determine the exact nature of the mutation. MASA was then used to screen the lymph nodes from these patients for the presence of the tumour-specific K-RAS transcript and the results were compared with K20 RT-PCR and histopathology from the same samples. Whilst K-RAS MASA was not as sensitive as K20 RT-PCR, there was substantial agreement between the assays. There were no K20-negative lymph nodes which were found to be K-RAS MASA-positive, whereas seven nodes in four patients were K20-positive and K-RAS-negative, in keeping with the differences in assay sensitivity. These results further validate K20 as a marker by providing greater certainty that what is being detected represents occult metastatic disease.

The clonal origin and clonal evolution of epithelial tumours

While the origin of tumours, whether from one cell or many, has been a source of fascination for experimental oncologists for some time, in recent years there has been a veritable explosion of information about the clonal architecture of tumours and their antecedents, stimulated, in the main, by the ready accessibility of new molecular techniques. While most of these new results have apparently confirmed the monoclonal origin of human epithelial (and other) tumours, there are a significant number of studies in which this conclusion just cannot be made. Moreover, analysis of many articles show that the potential impact of such considerations as patch size and clonal evolution on determinations of clonality have largely been ignored, with the result that a number of these studies are confounded. However, the clonal architecture of preneoplastic lesions provide some interesting insights --many lesions which might have been hitherto regarded as hyperplasias are apparently clonal in derivation. If this is indeed true, it calls into some question our hopeful corollary that a monoclonal origin presages a neoplastic habitus. Finally, it is clear, for many reasons, that methods of analysis which involve the disaggregation of tissues, albeit microdissected, are far from ideal and we should be putting more effort into techniques where the clonal architecture of normal tissues, preneoplastic and preinvasive lesions and their derivative tumours can be directly visualized in situ.

K-ras mutations, rectal crypt cells proliferation, and meat consumption in patients with left-sided colorectal carcinoma

It has been suggested that N-nitroso compounds derived from meat may increase the risk of K-ras mutations in the human colon. We sought evidence of associations between red meat consumption, frequency and type of K-ras mutations in resected tumours, and the rate of crypt cell proliferation (CCP) in the normal mucosa of patients with left-sided colorectal carcinoma. Meat consumption was assessed by food frequency questionnaire, and CCP was determined in rectal biopsies obtained prior to surgery. K-ras mutations in the resected tumours were determined using a PCR-based oligonucleotide hybridization assay. Fifteen K-ras mutations were detected in tumours from 43 patients; 13/15 in codon 12, 3/15 in codon 13, and 1/15 in both codons 12 and 13. All mutations were G-->A or G-->T transitions. There was no statistically significant difference between intakes of red meat in patients with a K-ras mutation (92.4 +/- 9.7 g/day) and those without (82.3 +/- 7.7 g/day). Rectal CCP was significantly higher in patients than in healthy controls, but there was no correlation with meat consumption or K-ras mutation. These data do not support the hypothesis that meat consumption is a risk factor for acquisition of K-ras mutations during colorectal carcinogenesis.

Molecular staging of colorectal cancer: K-ras mutation analysis of lymph nodes upstages Dukes B patients

PURPOSE

Multiple attempts have been made to improve the clinical/pathologic staging system of Dukes to focus adjuvant therapy decisions. The purpose of this study was to determine whether K-ras mutational status of regional nodes in patients with Dukes B2 colorectal cancer could be used to stage their disease more accurately.

METHODS

Using formalin-fixed, paraffin-embedded archival material, tumor samples were screened for K-ras mutations using a mutation-specific polymerase chain reaction method, followed by gel electrophoresis in a 96-well array. Patients with Dukes B2 tumors that have mutations in codon 12 or 13 of the K-ras gene were identified.

RESULTS

Mutational analysis of the lymph nodes from these patients revealed an 80 percent (16/20) incidence of the same mutations in regional lymph nodes. None of the four patients with mutation-free nodes developed recurrence compared with 37.5 percent (6/16) with K-ras positive lymph nodes.

CONCLUSIONS

The data suggest that patients with Dukes B2 colorectal cancers that have mutations in codon 12 or 13 of the K-ras gene are at high risk for the development of nodal metastases. Mutational analysis of the lymph nodes identifies high-risk patients who should be considered for adjuvant chemotherapy. Therefore, K-ras mutational analysis should be considered for molecular staging of colorectal cancer.

Hypermethylation of the MYF-3 gene in colorectal cancers: associations with pathological features and with microsatellite instability

Myf-3 is the human homologue of the murine Myo-D1 gene involved in muscle-cell differentiation. Using Southern blot analysis, we examined methylation of Myf-3 in histologically normal colonic mucosae, adenomas and carcinomas from a large series of patients with primary colorectal cancer. Hypermethylation of this gene in comparison with normal mucosa was observed in 88% of adenomas and in 99% of carcinomas. The pattern of Myf-3 methylation was similar in different areas of the same tumour, suggesting that methylation imbalances occur before the bulk of clonal-cell expansion. Significantly increased levels of Myf-3 methylation were observed in tumours which were more invasive, located in the proximal colon or from older patients. Patients whose tumours had extensive methylation showed a trend for shortened survival, though this was probably related to their being more invasive. Extensive methylation was significantly more frequent in tumours with microsatellite instability. Further work is required to determine whether the hypermethylation of Myf-3 observed in colorectal cancers is a specific alteration with functional significance or whether it reflects non-specific methylation imbalances occurring early during tumorigenesis.

Fidelity levels of DNA polymerases in tumorigenic state cells and serially transplantable tumor cells

It is well known that point mutations exist in oncogenes and tumor suppressor genes of tumor cells, and one of the causes of these mutations may be misincorporation by error-prone DNA polymerases. This hypothesis is supported by the observation of decreased fidelity levels of DNA polymerases in mouse spleen containing tumorigenic cells after infection with Friend virus, and in aged animals that suffer high rates of tumorigenesis. However, this decrease in fidelity is disadvantageous for tumor cells maintained by serial transplantation. Therefore, we measured the fidelity levels of DNA polymerases in tumor cells transplanted through many passages. The fidelity levels of DNA polymerases from Yoshida ascites hepatoma, Rhodamine sarcoma, mouse ascites hepatoma-134, and Ehrlich ascites carcinoma cells derived from rats and mice are very high for in-vitro DNA synthesis on synthetic polynucleotides. These results suggest that many kinds of mutant cells arise during tumorigenesis. Among these mutant cells, cells showing decreased DNA polymerase(s) fidelities are present and these cells may undergo cell death. On the other hand, cells with mutations in various oncogenes and tumor suppressor genes and without mutations in DNA polymerase genes may survive as serially transplantable tumor cells.

Mutations of p53 gene can be detected in the plasma of patients with large bowel carcinoma

AIMS

To attempt to detect p53 gene mutations in the plasma of patients with large bowel carcinoma.

METHODS

Plasma was collected from 20 control patients with no history of cancer and from 17 patients with large bowel carcinoma. Corresponding tumour and benign lymph node (control) samples for each of the carcinoma patients were obtained from paraffin blocks. A Dukes' stage was determined for each tumour. DNA was extracted from the plasma samples and the paraffin embedded tissue using previously described methods. A nested primer polymerase chain reaction protocol was used for the amplification of exons 5 to 8 of the p53 gene. "Cold" single strand conformational polymorphism (SSCP) was performed on mini gels and silver stained. Abnormal bands were excised, the DNA eluted, and reamplified for automated dye termination sequencing. Any sample showing an apparent mutation was rechecked from the original extracted DNA sample at least three times.

RESULTS

p53 gene mutations were not found in the control specimens. They were found in both the primary tumour and the plasma in three cases, in the primary tumour alone in one case, and in the plasma alone in two cases. One of the latter two cases also had metastatic transitional cell carcinoma of the bladder and the other had widespread metastatic deposits. One of the cases with mutant DNA in both the plasma and the primary was a Dukes' stage B tumour. The others were Dukes' C and Dukes' D.

CONCLUSIONS

p53 gene mutations can be detected in the plasma of some patients with large bowel carcinoma and these are concordant with those in the primary carcinomas.

Genetic diversity at the p53 locus between primary human colorectal adenocarcinomas and their lymph-node metastases

In both the primary tumor and associated lymph-node metastases of 40 cases of Dukes' C colorectal adenocarcinomas, exons 5 to 9 of the p53 tumor-suppressor gene were examined by PCR amplification and single-strand-conformation-polymorphism(SSCP) analysis. Mobility shifts indicating p53 mutations, which were confirmed by direct sequencing, were identified in 14 primary cancers (35%) and in 19 of the 40 lymph-node metastases (48%). In 12 cases (30%), the p53-mutation status in the primary cancer and its lymph-node metastases was identical. This result is compatible with the hypothesis that when a p53 mutation occurs before the establishment of lymph-node metastasis, it subsequently persists in the metastatic nodes. In 7 cases (18%), p53 mutations were identified in lymph-node metastases that were not concordant with the p53 status in the primary tumor. This finding can be explained by assuming that (1) p53 heterogeneity existing in the primary tumor is not reflected in all metastases and/or (2) new p53 mutations may occur during the development of metastatic lesions.

p53 accumulation and mutation are prognostic indicators of poor survival in human gastric carcinoma

The aim of our study was to examine the prognostic significance of p53 protein accumulation and gene mutation in a series of 116 gastric carcinomas from a low incidence population. Formalin-fixed, paraffin-embedded tumour sections were used to investigate p53 protein accumulation by immunostaining with monoclonal antibody (MAb) DO-7 and p53 gene mutation by single-strand conformation polymorphism analysis of exons 5-8. Nuclear p53 accumulation was detected in 23% of tumours and mutation in 28%. Concordance between the 2 alterations was observed in 73% of cases. p53 protein accumulation was more frequent in tumours with lymph node metastasis, while p53 mutations were more frequent in tumours from older patients. The histopathological parameters of depth of invasion, grade and histological type showed no significant associations with either p53 alteration. In univariate analysis, both alterations were associated with significantly shortened patient survival. The 5-year survival rate for patients with a p53 mutation was 9% compared to 42% for those without a mutation. In multivariate analysis adjusted for the other histopathological parameters, p53 gene mutation but not immunohistochemically-detected p53 protein accumulation was an independent prognostic indicator of poor survival in gastric carcinoma.