p53 and K-ras gene mutations correlate with tumor aggressiveness but are not of routine prognostic value in colorectal cancer

The MDM2 promoter polymorphism SNP309T-->G and the risk of uterine leiomyosarcoma, colorectal cancer, and squamous cell carcinoma of the head and neck

BACKGROUND

MDM2 acts as a principal regulator of the tumour suppressor p53 by targeting its destruction through the ubiquitin pathway. A polymorphism in the MDM2 promoter (SNP309) was recently identified. SNP309 was shown to result, via Sp1, in higher levels of MDM2 RNA and protein, and subsequent attenuation of the p53 pathway. Furthermore, SNP309 was proposed to be associated with accelerated soft tissue sarcoma formation in both hereditary (Li-Fraumeni) and sporadic cases in humans.

METHODS

We evaluated the possible contribution of SNP309 to three tumour types known to be linked with the MDM2/p53 pathway, using genomic sequencing or restriction fragment length polymorphism as screening methods. Three separate Finnish tumour materials (population based sets of 68 patients with early onset uterine leiomyosarcomas and 1042 patients with colorectal cancer, and a series of 162 patients with squamous cell carcinoma of the head and neck) and a set of 185 healthy Finnish controls were analysed for SNP309.

RESULTS

Frequencies of SNP309 were similar in all four cohorts. In the colorectal cancer series, SNP309 was somewhat more frequent in women and in patients with microsatellite stable tumours. Female SNP309 carriers were diagnosed with colorectal cancer approximately 2.7 years earlier than those carrying the wild type gene. However, no statistically significant association of SNP309 with patients' age at disease onset or to any other clinicopathological parameter was found in these three tumour materials.

CONCLUSION

SNP309 had no significant contribution to tumour formation in our materials. Possible associations of SNP309 with microsatellite stable colorectal cancer and with earlier disease onset in female carriers need to be examined in subsequent studies.

Novel P53 mutations detected by FAMA in colorectal cancers

BACKGROUND

The aim of the study was to identify p53 gene mutations by FAMA (fluorescence-assisted mismatch analysis) in colorectal cancers.

PATIENTS AND METHODS

Analytical scanning of the p53 gene (exons 5-9) was performed in colon cancer samples from 44 consecutive patients by FAMA. FAMA is a semiautomatic scanning approach based on the chemical cleavage of the mismatch in fluorescently labeled heteroduplex DNA, obtained from the combination of a normal and a mutated allele. FAMA has already shown optimal levels of diagnostic accuracy and sensitivity in detecting gene mutations (nucleotide substitutions, insertions/deletions) both at the germline and somatic level. The peculiar feature of FAMA is its ability to detect and localize mutations, by a redundant pattern of signals due to fluorescent DNA fragments generated by chemical cleavage. Moreover, previous data have demonstrated that normal contaminating DNA from stromal cells in the sample does not affect the sensitivity of the procedure, leading to the identification of the mutation even when the ratio mutant/normal allele is 10%.

RESULTS

Eighteen mutations (12 missense, one nonsense, two deletions, three nucleotide substitutions at the level of the splice-junctions) and two polymorphisms were detected by FAMA in 17 patients (39%) and then confirmed by automated sequence analysis. Six of 18 mutations (33%) were not previously reported for colon cancer samples and two of 18 lesions (11%) were identified as novel p53 mutations.

CONCLUSIONS

Analytical scanning of the p53 gene by FAMA in DNA from colon cancer samples provides a sensitive, accurate and specific diagnostic procedure for routine clinical application.

The p53 pathway promotes efficient mitochondrial DNA base excision repair in colorectal cancer cells

The tumor suppressor p53 plays a central role in the DNA damage response. p53 enhances base excision repair (BER), in part, through direct interaction with the repair complex. Mitochondrial DNA (mtDNA) is repaired by a mtBER pathway. Many colorectal cancers harbor mtDNA mutations that are associated with poor prognosis. In addition to modulating the apoptotic response, mitochondria-localized p53 also stimulates mtBER. However, the mechanisms by which p53 enhances colorectal cancer mtBER after stress remain unclear. To explore this, we used colorectal cancer cells isogenic for p53 (HCT116p53+/+ and HCT116p53-/-). p53+/+ cells more efficiently repaired H(2)O(2) damaged DNA in vivo as measured by semiquantitative mtDNA displacement loop PCR. Mitochondrial extracts from p53+/+ cells more efficiently stimulated (32)P-dCTP incorporation into a uracil-oligonucleotide. Recombinant p53 complemented p53-/- mitochondrial extract repair of uracil or 8-oxo-G-containing oligonucleotides. As a measure of DNA glycosylase activity, p53+/+ mitochondrial extracts more efficiently incised uracil or 8-oxo-G oligonucleotides, although recombinant p53 could not stimulate oligonucleotide incision. p53 did not influence mitochondrial apurinic/apyrimidinic endonuclease activity measured by incision of a tetrahydrofuran-oligonucleotide. p53+/+ mitochondrial extracts had higher DNA polymerase-gamma activity measured by (32)P-dCTP incorporation into a single-nucleotide gap oligonucleotide, and recombinant p53 complemented p53-/- mitochondrial extract DNA polymerase-gamma activity. mtDNA ligase activity was not affected by p53 status. p53 protein was detected in an inner mitochondrial membrane subfraction containing components of the mtBER complex. Our data suggest that an intact p53 pathway stimulates specific mtBER steps and provides mechanistic insight into the development of mtDNA mutations in colorectal cancer.

Transcriptional targets of hepatocyte growth factor signaling and Ki-ras oncogene activation in colorectal cancer

Both Ki-ras mutation and hepatocyte growth factor (HGF) receptor Met overexpression occur at high frequency in colon cancer. This study investigates the transcriptional changes induced by Ki-ras oncogene and HGF/Met signaling activation in colon cancer cell lines in vitro and in vivo. The model system used in these studies included the DLD-1 colon cancer cell line with a mutated Ki-ras allele, and the DKO-4 cell line generated from DLD-1, with its mutant Ki-ras allele inactivated by targeted disruption. These cell lines were transduced with cDNAs of full-length Met receptor. Microarray transcriptional profiling was conducted on cell lines stimulated with HGF, as well as on tumor xenograft tissues. Overlapping genes between in vitro and in vivo microarray data sets were selected as a subset of HGF/Met and Ki-ras oncogene-regulated targets. Using the Online Predicted Human Interaction Database, novel HGF/Met and Ki-ras regulated proteins with putative functional linkage were identified. Novel proteins identified included histone acetyltransferase 1, phosphoribosyl pyrophosphate synthetase 2, chaperonin containing TCP1, subunit 8, CSE1 chromosome segregation 1-like (yeast)/cellular apoptosis susceptibility (mammals), CCR4-NOT transcription complex, subunit 8, and cyclin H. Transcript levels for these Met-signaling targets were correlated with Met expression levels, and were significantly elevated in both primary and metastatic human colorectal cancer samples compared to normal colorectal mucosa. These genes represent novel Met and/or Ki-ras transcriptionally coregulated genes with a high degree of validation in human colorectal cancers.

MDM2 antagonists activate p53 and synergize with genotoxic drugs in B-cell chronic lymphocytic leukemia cells

B-cell chronic lymphocytic leukemia (B-CLL) is characterized by the accumulation of long-lived CD5(+) B lymphocytes. Several drugs currently used in the therapy of B-CLL act, at least partially, through activation of the p53 pathway. Recently, nongenotoxic small-molecule activators of p53, the nutlins, have been developed that inhibit p53-MDM2 binding. We have investigated the antitumor potential of nutlin-3 in B-CLL and find that it can activate the p53 pathway and effectively induce apoptosis in cells with wild-type p53, including cells with dysfunctional ataxia telangiectasia mutated, but not mutant p53. Nutlin-3 stabilized p53 and induced p53 target genes, including MDM2, p21(CIP1), PUMA, BAX, PIG3, and WIG1. Nutlin-3 synergized with the genotoxic drugs doxorubicin, chlorambucil, and fludarabine, but not with acadesine, which induces p53-independent apoptosis. Normal human T cells showed lower sensitivity to nutlin-3 than B-CLL cells and no synergism with the genotoxic drugs. These results suggest that MDM2 antagonists alone or in combination with chemotherapeutic drugs may offer a new treatment option for B-CLL.

Refining molecular analysis in the pathways of colorectal carcinogenesis

BACKGROUND & AIMS

In the stepwise model, specific genetic and epigenetic changes accumulate as colorectal adenomas progress to carcinomas (CRCs). CRCs also acquire global phenotypes, particularly microsatellite instability (MSI) and aneuploidy/polyploidy (chromosomal instability, CIN). Few changes specific to MSI-low or CIN+ cancers have been established.

METHODS

We investigated 100 CRCs for: mutations and loss of heterozygosity (LOH) where appropriate, of APC, K-ras, BRAF, SMAD4, and p53; deletion on 5q around APC and 18q around SMAD4; total chromosomal-scale losses and gains; MSI; and CIN.

RESULTS

As expected, CIN- cancers had fewer chromosomal changes overall than CIN+ lesions, but after correcting for this, 5q deletions alone predicted CIN+ status. 5q deletions were not, however, significantly associated with APC mutations, which were equally frequent in CIN+ and CIN- tumors. We therefore found no evidence to show that mutant APC promotes CIN. p53 mutations/LOH were more common in CIN+ than CIN- lesions, and all chromosomal amplifications were in CIN+ tumors. CIN- cancers could be subdivided according to the total number of chromosomal-scale changes into CIN-low and CIN-stable groups; 18q deletion was the best predictor, being present in nearly all CIN-low lesions and almost no CIN-stable tumors. MSI-low was not associated with CIN, any specific mutation, a mutational signature, or clinicopathologic characteristic.

CONCLUSIONS

Overall, the components of the stepwise model (APC, K-ras, and p53 mutations, plus 18q LOH) tended to co-occur randomly. We propose an updated version of this model comprising 4 pathways of CRC pathogenesis, on the basis of 5q/18q deletions, MSI (high/low), and CIN (high/low/stable).

Determination of TP53 Mutation Is More Relevant Than Microsatellite Instability Status for the Prediction of Disease-Free Survival in Adjuvant-Treated Stage III Colon Cancer Patients

Purpose

Microsatellite instability (MSI), TP53 mutation, and KRAS mutation status have been reported as prognostic factors in colon cancer. Most studies, however, have included heterogeneous groups of patients with respect to cancer stage. We determined the prognostic relevance of high-frequency MSI (MSI-H), TP53 mutations, and KRAS mutations in a well-defined group of patients with stage III colon cancer (N = 391), randomly assigned for adjuvant treatment with fluorouracil-based chemotherapy.

Methods

Three hundred ninety-one tumor specimens were available. MSI was determined in 273 specimens, and mutation analyses of TP53 and KRAS were performed in 220 and 205 specimens, respectively.

Results

In a univariate analysis, MSI-H (44 of 273; 16%) was associated with a longer disease-free survival (DFS; P = .038), but in a multivariate model adjusting for nodal involvement, histology, invasion, and grade of tumor, the association of MSI status with DFS did no longer reach statistical significance, though the risk estimate for microsatellite stability versus MSI-H tumors did not change much. Mutant TP53, found in 116 (53%) of 220 tumors, was associated with a shorter DFS, both in univariate (P = .009) and multivariate analyses (P = .018), whereas KRAS mutations (58 of 205; 28%) did not show any prognostic significance.

Conclusion

Both mutant TP53 and MSI-H seem to be prognostic indicators for disease-free survival, but only TP53 retains statistical significance after adjusting for clinical heterogeneity. Thus, in adjuvantly treated patients with stage III colon cancer, presence or absence of a TP53 mutation should be considered as a better predictor for DFS than MSI status.

Control of colorectal metastasis formation by K-Ras

Mutational activation of the K-Ras proto-oncogene is frequently observed during the very early stages of colorectal cancer (CRC) development. The mutant alleles are preserved during the progression from pre-malignant lesions to invasive carcinomas and distant metastases. Activated K-Ras may therefore not only promote tumor initiation, but also tumor progression and metastasis formation. Metastasis formation is a very complex and inefficient process: Tumor cells have to disseminate from the primary tumor, invade the local stroma to gain access to the vasculature (intravasation), survive in the hostile environment of the circulation and the distant microvascular beds, gain access to the distant parenchyma (extravasation) and survive and grow out in this new environment. In this review, we discuss the potential influence of mutant K-Ras on each of these phases. Furthermore, we have evaluated the clinical evidence that suggests a role for K-Ras in the formation of colorectal metastases.

Mutant KRAS, chromosomal instability and prognosis in colorectal cancer

The RAS gene family provides a global effect on gene expression by encoding small GTP-binding proteins which act as molecular switches connecting extracellular signals with nuclear transcription factors. While wild type RAS proteins are switched off shortly after activation, mutant RAS proteins remain constitutively activated leading to complex interactions among their downstream effectors. For some human tumor types, these interactions were shown to contribute to cancer genesis and progression by inducing changes in cell survival, apoptosis, angiogenesis, invasion and metastasis. This review addresses the controversial link of KRAS mutations in colorectal cancer with chromosomal instability and patient prognosis.

Hypermethylation of the prostacyclin synthase (PTGIS) promoter is a frequent event in colorectal cancer and associated with aneuploidy

Inactivation of specific tumor suppressor genes by transcriptional silencing associated with hypermethylation of the promoter is a common event in cancer. We have applied the amplification of intermethylated sites (AIMS) technique to a 100 human colorectal cancers and seven cell lines to identify recurrent alterations that may unveil silenced tumor suppressor genes. Bisulfite sequencing was used to confirm differential DNA methylation results. Gene expression analysis was performed by real-time RT-PCR. An AIMS band recurrently displayed in tumors but not in normal tissues was isolated and identified as part of the CpG island of the prostacyclin synthase (PTGIS) gene promoter. PTGIS promoter was hypermethylated in 43 out of 100 colorectal cancers and in all cell lines. Bisulfite sequencing and clonal analysis confirmed the results obtained by AIMS and demonstrated biallelic hypermethylation of PTGIS promoter. Hypermethylation of the PTGIS promoter was associated with diminished gene expression, that was restored after treatment with demethylating and histone deacetylases inhibitor agents. PTGIS hypermethylation was associated with aneuploidy and p53 mutations. In the adjusted model, PTGIS methylation, but not p53 mutation, maintained the association with aneuploidy. We conclude that epigenetic inactivation of the PTGIS gene is a recurrent alteration in colorectal carcinogenesis.

Association of k-ras, b-raf, and p53 status with the treatment effect of bevacizumab

BACKGROUND

A recent phase III trial showed that the addition of bevacizumab, a monoclonal antibody to vascular endothelial growth factor-A, to first-line irinotecan, 5-fluorouracil, and leucovorin (IFL) prolonged median survival in patients with metastatic colorectal cancer. We carried out a retrospective analysis of patients in the trial to evaluate whether mutation status of k-ras, b-raf, or p53 or P53 expression could predict which patients were more likely to respond to bevacizumab.

METHODS

Microdissected tumors from 295 patients (274 primary tumors, 21 metastases) were subject to DNA sequence analysis to identify mutations in k-ras, b-raf, and p53. Nuclear P53 expression was determined by immunohistochemistry. Hazard ratios and 95% confidence intervals (CI) for overall survival were estimated using Cox regression analysis.

RESULTS

In all biomarker subgroups, estimated hazard ratios for risk of death were less than 1 for bevacizumab-treated patients as compared with those for placebo-treated patients. Mutations in k-ras and/or b-raf were observed in 88 of 213 patients (41%). Hazard ratios for death among patients with tumors with wild-type k-ras/b-raf status, as compared with those of patients with mutations in one or both genes, were 0.51 (95% CI = 0.28 to 0.95) among those treated with IFL plus bevacizumab and 0.66 (95% CI = 0.37 to 1.18) among those treated with IFL plus placebo. Mutations in p53 were found in 139 of 205 patients (68%), and P53 was overexpressed in 191 of 266 patients (72%); neither p53 mutation nor P53 overexpression was statistically significantly associated with survival.

CONCLUSIONS

We did not find a statistically significant relationship between mutations of k-ras, b-raf, or p53 and the increase in median survival associated with the addition of bevacizumab to IFL in metastatic colorectal cancer.

Somatic mutations in human cancer: applications in molecular epidemiology

The tumour suppressor protein p53 mediates cell-cycle arrest, DNA repair and apoptosis after activation by multiple forms of cellular stresses. When activated, this "master protein" modulates its response depending on the type and intensity of the stress. The TP53 gene with its nearly 20,000 described mutations is the most mutated gene in cancer. Most mutations are missense and occur at over 200 codons within the central portion of the gene. In several cancers, the distribution of mutation types and sites follow a specific pattern reflecting the effects of environmental mutagens. An example for such a "mutagen fingerprint" is TP53 mutation at codon 249 in hepatocellular carcinoma in regions of the world characterised by high levels of the mutagen aflatoxin B1 and endemic HBV infection. Recently, TP53 mutations have been detected in surrogate sources of genetic material such as free circulating DNA isolated from plasma. Plasma TP53 mutations can be detected in the blood of pre-cancer and cancer patients, with potential application for early cancer detection. Thus, TP53 mutations have multiple applications as markers of mutagenic exposures, or as intermediate end-points in assessment of cancer occurrence and progression.

Prognostic and predictive factors in colorectal cancer: Kirsten Ras in CRC (RASCAL) and TP53CRC collaborative studies

Mutations in the Ki-ras and TP53 genes are the most frequently observed genetic alterations in colorectal cancer (CRC). Ki-ras mutations are mostly found in codons 12 and 13, and less in codon 61. The majority of the TP53 mutations occur in the core domain which contains the sequence-specific DNA binding activity of the protein, and they results in loss of DNA binding. Few centres have sufficient patients to collect detailed information in the large numbers required to determine the impact of individual ki-ras and TP53 genotypes on outcome. Moreover, it has been reported that specific genetic alterations, and not any mutation, might play a different biological role in cancer progression. For these principal reasons, two collaborative studies have been conducted (the RASCAL and the TP53-CRC Collaborative Studies) with the aim of investigating the prognostic role of any, and specific, Ki-ras and TP53 mutations in CRC progression. The results obtained from the RASCAL studies suggest that Ki-ras mutations might have an effect on the survival rate of CRC patients, and that the specific codon 12 glycine/valine mutation might play a role in the progression of this neoplasia. The results of the TP53-CRC International Collaborative Study demonstrate the importance of primary tumor site when analyzing the prognostic value of TP53 mutations in CRC. In addition, different types of TP53 mutation might play a pivotal role in determining the biological behavior of CRC from different sites and hence the prognosis of patients. This meta-analysis produced evidence for interesting tumor site differences in the predictive value of TP53 mutation for survival benefit from 5FU chemotherapy.

APC, K-ras, and p53 Gene Mutations in Colorectal Cancer Patients: Correlation to Clinicopathologic Features and Postoperative Surveillance

Current researches have proposed a genetic model for colorectal cancer (CRC), in which the sequential accumulation of mutations in specific cancer-related genes, including adenomatous polyposis coli (APC), K- ras, and p53, drives the transition from normal epithelium through increasing adenomatous dysplasia to colorectal cancer. To identify patients with an increased risk of tumor recurrence or metastasis and evaluate the prognostic values of APC, K- ras, and p53 gene mutations, we investigated the frequency of these three mutated genes in tumors and sera of CRC patients. APC, K- ras, and p53 gene mutations in primary tumor tissues and their paired preoperative serum samples of 118 CRC patients were detected by using polymerase chain reaction– single strand conformation polymorphism (PCR-SSCP) analysis, followed by direct DNA sequencing of the PCR-amplified genomic DNA. Subsequently, serum molecular markers were analyzed for their correlation with patients’ clinicopathologic features and presence of postoperative recurrence/metastasis. We did not observe any significant difference in the association of APC or K- ras or p53 gene mutations in primary tumors with patients’ demographic data (all were P > 0.05). In contrast, both serum APC and p53 molecular markers were closely correlated with lymph node metastasis and TNM stage (both P < 0.05). Moreover, the serum overall molecular markers (at least one of the three markers) were prominently associated with depth of tumor invasion ( P = 0.033), lymph node metastasis ( P < 0.001), and TNM stage ( P < 0.001). In addition, a significantly higher postoperative metastasis/recurrence rate in patients positive for overall molecular markers compared to those negative for these molecular markers were also demonstrated ( P < 0.001). APC and K- ras molecular markers were more frequently observed in patients with locoregional metastasis (both P < 0.05), while p53 molecular marker was usually detected in the cases of peritoneal metastasis ( P = 0.004). Our findings suggest that serum molecular markers are potentially useful in the determination of colorectal cancer patients harboring gene mutations at high risk of metastasis. Serial analysis is warranted in order to assess their long-term prognostic significance and the therapeutic implications.

Differential DNA hypermethylation and hypomethylation signatures in colorectal cancer

Cancer cells are characterized by a generalized disruption of the DNA methylation pattern involving an overall decrease in the level of 5-methylcytosine together with regional hypermethylation of particular CpG islands. The extent of both DNA hypomethylation and hypermethylation in the tumor cell is likely to reflect distinctive biological and clinical features, although no studies have addressed its concurrent analysis until now. DNA methylation profiles in sporadic colorectal carcinomas, synchronous adenoma-carcinoma pairs and their matching normal mucosa were analyzed by using the amplification of inter-methylated sites (AIMS) method. A total of 208 AIMS generated sequences were tagged and evaluated for differential methylation. Global indices of hypermethylation and hypomethylation were calculated. All tumors displayed altered patterns of DNA methylation in reference to normal tissue. On average, 24% of the tagged sequences were differentially methylated in the tumor in regard to the normal pair with an overall prevalence of hypomethylations to hypermethylations. Carcinomas exhibited higher levels of hypermethylation than did adenomas but similar levels of hypomethylation. Indices of hypomethylation and hypermethylation showed independent correlations with patient's sex, tumor staging and specific gene hypermethylation. Hierarchical cluster analysis revealed two main patterns of DNA methylation that were associated to particular mutational spectra in the K-ras and the p53 genes and alternative correlates of hypomethylation and hypermethylation with survival. We conclude that DNA hypermethylation and hypomethylation are independent processes and appear to play different roles in colorectal tumor progression. Subgroups of colorectal tumors show specific genetic and epigenetic signatures and display distinctive correlates with overall survival.

Organochlorine exposure and colorectal cancer risk

Organochlorine compounds have been linked to increased risk of several cancers. Despite reductions in their use and fugitive release, they remain one of the most important groups of persistent pollutants to which humans are exposed, primarily through dietary intake. We designed a case-control study to assess the risk of colorectal cancer with exposure to these chemicals, and their potential interactions with genetic alterations in the tumors. A subsample of cases (n = 132) and hospital controls (n = 76) was selected from a larger case-control study in Barcelona, Catalonia, Spain. We measured concentrations in serum of several organochlorines by gas chromatography. We assessed point mutations in K-ras and p53 genes in tissue samples by polymerase chain reaction/single-strand conformation polymorphism and assessed expression of p53 protein by immunohistochemical methods. An elevated risk of colorectal cancer was associated with higher serum concentrations of mono-ortho polychlorinated biphenyl (PCB) congeners 28 and 118. The odds ratio for these mono-ortho PCBs for middle and higher tertile were, respectively, 1.82 [95% confidence interval (CI), 0.90-3.70] and 2.94 (95% CI, 1.39-6.20). Alpha-hexachlorocyclohexane, hexachlorobenzene, and p,p'-DDE (4,4'-dichlorodiphenyltrichloroethene) showed nonsignificant increases in risk. Risk associated with mono-ortho PCBs was slightly higher for tumors with mutations in the p53 gene but was not modified by mutations in K-ras. Mono-ortho PCBs were further associated with transversion-type mutations in both genes. These results generate the hypothesis that exposure to mono-ortho PCBs contributes to human colorectal cancer development. The trend and magnitude of the association, as well as the observation of a molecular fingerprint in tumors, raise the possibility that this finding may be causal.

Genetic Alterations in Locally Advanced Stage II/III Colon Cancer: A Search for Prognostic Markers

Heterogeneity in advanced colon cancer leads to different results from adjuvant chemotherapy. To identify groups of patients who may need adjuvant treatment, molecular staging and correlation with clinical data may be helpful in classifying histologically similar tumors. Colon cancer develops through a multistep process with an accumulation of multiple genetic alterations that are often the cause of a form of genomic instability. The 2 best known mechanisms of genomic instability are chromosomal instability (CIN) and microsatellite instability (MSI). The CIN phenotype is found in approximately 85% of sporadic colon cancers and is characterized by aneuploidy, multiple chromosomal rearrangements, and an accumulation of somatic mutations in oncogenes such as K-ras and tumor suppressor genes such as TP53 and APC. The MSI phenotype is associated with small insertions and deletions mainly in repetitive sequences (microsatellites) and is found in approximately 15% of cases. This instability, often referred to as high-frequency MSI (MSI-H), is caused by defects of the mismatch repair system, which is involved in repairing DNA errors that arise during DNA replication. Clear-cut correlations between the somatic genetic alterations in tumors and the clinical behavior of the tumor are rare. Only a few markers, such as MSI-H and TP53, seem to have a prognostic value. Mutations in the TP53 gene are associated with an aggressive tumor growth and subsequent reduced survival, whereas MSI-H seems to be correlated with a favorable outcome. In general, predicting biologic behavior of in particular stage III colon cancers is difficult and remains a great clinical problem.

Expression of valosin-containing protein in colorectal carcinomas as a predictor for disease recurrence and prognosis

PURPOSE

Valosin-containing protein (VCP or p97) is associated with antiapoptotic function and metastasis via activation of the nuclear factor-kappaB signaling pathway. The present study was designed to investigate the prognostic significance of VCP expression in colorectal adenocarcinoma.

EXPERIMENTAL DESIGN

We analyzed VCP expression immunohistochemically in 129 patients with colorectal carcinoma ages 35-84 years. The staining intensity of tumor cells was categorized as either weaker-to-equal (low VCP expression) or stronger (high expression) than that in noncancerous colonic mucosa. We also analyzed 8 colorectal adenomas and 10 metastatic foci.

RESULTS

Low VCP expression was noted in 41 (31.8%) cases and high expression in 88 (68.2%) cases. A low level of VCP expression was noted in all adenomas, whereas a high level was seen in all metastatic tumors. A significant difference was observed in depth of invasion (T(1-2) versus T(3-4), P < 0.05), presence or absence of venous invasion (P < 0.05), and tumor stage (I and II versus III and IV; P < 0.05) between adenocarcinomas with low and high VCP expression. Patients with high VCP-expressing tumors had a higher recurrence rate (P < 0.001) and poorer disease-free and overall survival (P < 0.01 and P < 0.05, respectively) compared with the low expression group. Multivariate analysis revealed VCP expression level to be an independent prognosticator for both disease-free and overall survival. VCP level was an indicator of disease-free survival in both stage II and III (pathological Tumor-Node-Metastasis classification, P < 0.05 and <0.01, respectively).

CONCLUSIONS

A high expression level of VCP in tumors is a poor prognostic marker in patients with colorectal carcinomas.

Systematic review of genetic influences on the prognosis of colorectal cancer

Background

In terms of genetics, colorectal cancer is one of the best understood of all malignant diseases. Genetic influences on prognosis may have far-reaching implications, especially for the design of surgical and chemoradiotherapeutic regimens. However, their significance in determining prognosis remains unclear. This study aimed to review the literature on the specific role of key genes in determining the survival of patients with colorectal cancer.

Methods

A Medline search was carried out to identify all original scientific papers relating colorectal cancer genetics to patient survival, up to December 2002. Cochrane and Embase databases were also searched. Identified articles were retrieved and searched carefully for additional information. This review includes K-ras, p53, DCC, NM23 and DNA mismatch repair genes.

Results and conclusion

Conflicting evidence exists as to the prognostic significance of genes commonly implicated in the pathogenesis of colorectal carcinoma. Possible causes for such discrepancy include differences in study methods and laboratory techniques, variable duration of follow-up, statistical differences in study power, and heterogeneity in study populations. Future studies should adopt standardized protocols to define clinically relevant genetic observations.

p53 is an independent pre-treatment markers for long-term survival in stage II and III colorectal cancers: an analysis of interaction between genetic markers and fluorouracil-based adjuvant therapy

One hundred and thirty-eight stage II and III colorectal cancer patients were included to evaluate the prognostic significance of genetic markers (including mutations of the p53, K-ras genes, and microsatellite instability) on the response to 5-fluorouracil (FU)-based post-operative adjuvant therapies (PAT). When stratified by PAT and adjusting for other prognostic variables, presence of p53 mutation was associated with a poor outcome (hazard ratio (HR)=3.1, 95% confidence interval (CI), 0.9-11.0) among patients without PAT. Our data confirmed that p53 mutation is an independent pre-treatment factor in stage II and III colorectal cancer after curative resection.

Simultaneous mutations in K-ras and TP53 are indicative of poor prognosis in sporadic colorectal cancer

Despite the fact that the mutations in K-ras codon 12 and TP53 are common abnormalities in colorectal cancer, the determination of K-ras mutation combined with TP53 gene mutation, with diagnostic and prognostic purposes is still controversial. We have analyzed K-ras and TP53 mutations in 77 sporadic colorectal adenocarcinomas by means of polymerase chain reaction and sequencing. We observed a negative correlation between both K-ras and TP53 mutations. Patients with mutations in K-ras but not in TP53 exhibited worse survival rates than those with mutations in TP53 and not in K-ras. Moreover, we found the worst outcome in patients with mutations in both K-ras and TP53. These results may relate to the previously published data about primary human and rodent cells, in which transformation by Ras require either a cooperating oncogene or the inactivation of tumor suppressors such as p53 or p16. In conclusion, simultaneous mutations in K-ras and TP53 are indicative of a worse prognosis in sporadic colorectal cancer.

Molecular lesions in colorectal cancer: impact on prognosis? Original data and review of the literature

BACKGROUND

In the Dukes' B and C stages of colorectal carcinoma there are considerable variations in the observed courses of the disease. Since post-operative chemotherapy in patients with Dukes' C (node-positive) colon carcinoma has been demonstrated to be effective in improving overall-survival, a more exact prognosis assessment gains additional significance and therapeutic relevance.

DISCUSSION

One also hopes to derive improved prognostic factors from the clarification of the molecular pathogenesis. Because of its frequency and the accessibility and recognizability of its developmental stages colorectal carcinoma is among the best investigated of all solid tumors. Despite a multitude of suggested molecular candidate markers none of these changes has yet been able enter the everyday life of the clinic. However, it is to be expected that some of the molecular alterations presently discussed will gain importance before long in the clinical treatment of patients with colorectal carcinoma.

CONCLUSION

Considering also our own findings, this review presents the latest developments in the scientific discussion of the tumor suppressor/oncogenes p53, k-ras, and DCC, biochemical determinants of the 5-fluorouracil metabolism, and defects of the DNA repair system.

Overexpression of the Wilms' tumor gene WT1 in colorectal adenocarcinoma

Expression of the Wilms' tumor gene WT1 was examined in 59 cases of colorectal adenocarcinoma to examine the involvement of WT1 in tumorigenesis. Quantitative real-time reverse transcription-polymerase chain reaction (RT-PCR) showed that WT1 mRNA was expressed in the range from 7.2 x 10(-5) to 4.9 x 10(-1) levels (WT1 expression level in K562 leukemic cells was defined as 1.0) in all (100%) of the 28 cases of colorectal adenocarcinoma examined, and that the WT1 mRNA expression levels were higher in 20 (71%) of the 28 cases compared to those of normal-appearing mucosal tissues examined. Immunohistochemical analysis using an anti-WT1 antibody was performed on 46 cases of colorectal adenocarcinoma (15 of the 28 cases with WT1 mRNA expression and 31 newly collected cases), and the expression of WT1 protein was detected in 41 (89%) of the 46 cases. The direct sequencing analysis of the WT1 genomic DNA showed no mutations in any of the 10 exons of the WT1 gene in any of 5 different colorectal adenocarcinomas. These results may indicate an important role of the wild-type WT1 gene in tumorigenesis of colorectal adenocarcinoma.

Distribution of genetic variants in preneoplastic areas of colorectal tumours

AIMS

Loss of heterozygosity (LOH) may vary almost randomly within a colorectal tumour due to the heterogeneous morphologic character of these tumours. Despite this, as a rule, single biopsies are the source of genetic material used in studies of markers important for prognosis, clinical behaviour of the disease, or susceptibility of specific tumours to different treatment modalities.

METHODS

To evaluate the importance of intratumoural variation for the results of analysis of LOH and point mutations in colorectal cancer and to determine the frequency of genetic alterations in different types of pre-neoplastic areas of the tumours, 36 consecutively operated patients with colorectal cancer were studied. After fixation, specimens were mounted on large slides containing the whole tumour. The specimens were sub classified into different areas defined as normal tissue, normal tissue closely adjacent the tumour mass, adenoma, dysplasia and invasive cancer cells. These areas were dissected and subjected to DNA extraction.

RESULTS

The extracted genomic DNA was studied for LOH at chromosome 5q, 17p, and 18q and for k-ras mutations. Overall, a correlation between the intratumoural degree of neoplastic progression and the frequency of LOH and k-ras mutations was seen. These correlations were significant (p<0.008) except for dysplasia/adenomatous tissue versus invasive cancer. Microsatellite instability was found in 9% of the tumours, all except one in invasive parts of the tumours.

CONCLUSIONS

This study demonstrates a statistical correlation between intratumoural differences in neoplastic degree of dedifferentiation and genetic instability in terms of LOH and point mutations of the k-ras gene in colorectal carcinoma. The importance of a careful dissection in order to localise the region with the highest probability of genetic aberrations and multiple biopsing must not be neglected. The observation that the prevalence of k-ras mutations and LOH are correlated to the degree of dedifferentiation within a colorectal tumour is in line with the concept that selected cell clones are responsible for the neoplastic progression of the tumour.

Molecular biomarkers of colorectal carcinogenesis and their role in surveillance and early intervention

Modern medicine is increasingly focused towards population surveillance for disease, coupled with the implementation of preventative measures applied to 'at-risk' patients. Surveillance in colorectal cancer is limited by the cost and risk of endoscopy. Trials of putative chemopreventive agents in colorectal cancer are hampered by difficulties in following up large cohorts of patients over long periods of time to ascertain the clinical effect. Research into possible pathways of colorectal carcinogenesis has revealed a range of biological intermediates which could be used in surveillance, the identification of high risk populations and early diagnosis of cancer. The aim of this paper was to review the possible role of biomarkers in surveillance and the timing of intervention. A literature review using both Medline and Web of Science was performed from 1995 onwards using keywords: biomarkers, colorectal cancer, carcinogenesis, chemoprevention, surveillance and screening. Research has identified many potential biomarkers, such as cyclooxygenase-2 (COX-2), oxidative DNA adducts and glutathione S-transferase (GST) polymorphisms, which could be applied in a clinical setting to screen for and detect colorectal cancer. Molecular biomarkers, such as COX-2, oxidative DNA adducts and GST polymorphisms offer new prospects in the detection of early colorectal cancer, surveillance of high-risk populations and prediction of the clinical effectiveness of chemopreventive drugs. Their role could be extended into surgical surveillance for potentially operable disease and post-operative follow-up for disease recurrence. Research should be directed at assessing complementary biomarkers to increase clinical effectiveness in determining management options for patients.

TP53 mutation in colorectal cancer

Approximately half of all colorectal cancers show p53 (TP53) gene mutations, with higher frequencies observed in distal colon and rectal tumors and lower frequencies in proximal tumors and those with the microsatellite instability or methylator phenotypes. Alterations to this gene appear to have little or no prognostic value for colorectal cancer patients treated by surgery alone, but are associated with worse survival for patients treated with chemotherapy. There is some evidence that different p53 mutations are associated with different clinical features including prognosis and response to therapy, although further large studies are required to confirm this. Several in vitro, animal and clinical studies have shown that normal p53 is required for the response of colorectal cancers to 5-fluorouracil-based chemotherapy. This should be confirmed by additional retrospective cohort studies and by the incorporation of P53 status in ongoing and future clinical trials. The evaluation of p53 overexpression, using a standardized immunohistochemical (IHC) procedure, could be a clinically useful marker for the identification of colorectal cancer patients likely to benefit from the standard chemotherapy regime currently used for this disease.

Specific codon 13 K-ras mutations are predictive of clinical outcome in colorectal cancer patients, whereas codon 12 K-ras mutations are associated with mucinous histotype

BACKGROUND

K-ras mutations, one of the earliest events observed in colorectal carcinogenesis, are mostly found in codons 12 and 13, and less frequently in codon 61, all three of which are estimated to be critical for the biological activity of the protein. Nevertheless the prognostic significance of such mutations remains controversial. Our purpose was to assess whether any or specific K-ras mutations in primary colorectal cancer had prognostic significance and were linked to clinico-pathological parameters.

PATIENTS AND METHODS

Paired tumor and normal tissue samples from a consecutive series of 160 untreated patients (median of follow up 71 months), undergoing resective surgery for primary colorectal carcinoma, were prospectively studied for K-ras mutations by PCR/single strand conformation polymorphism sequencing.

RESULTS

Seventy-four of the 160 (46%) primary colorectal carcinomas presented mutations in K-ras: 54% in codon 12, 42% in codon 13 (particularly G-->A transition) and 4% in both. Codon 12 K-ras mutations were associated with mucinous histotype (P <0.01), while codon 13 K-ras mutations were associated with advanced Dukes' stage (P <0.05), lymph-node metastasis (P <0.05) and high S-phase fraction (P <0.05). Multivariate analysis showed that codon 13 K-ras mutations, but not any mutation, were independently related to risk of relapse or death.

CONCLUSIONS

Our results suggest that codon 12 K-ras mutations may have a role in the mucinous differentiation pathway, while codon 13 mutations have biological relevance in terms of colorectal cancer clinical outcome.

Single nucleotide polymorphism seeking long term association with complex disease

Successful investigation of common diseases requires advances in our understanding of the organization of the genome. Linkage disequilibrium provides a theoretical basis for performing candidate gene or whole-genome association studies to analyze complex disease. However, to constructively interrogate SNPs for these studies, technologies with sufficient throughput and sensitivity are required. A plethora of suitable and reliable methods have been developed, each of which has its own unique advantage. The characteristics of the most promising genotyping and polymorphism scanning technologies are presented. These technologies are examined both in the context of complex disease investigation and in their capacity to face the unique physical and molecular challenges (allele amplification, loss of heterozygosity and stromal contamination) of solid tumor research.

Cancer genetics and their application to individualised medicine

One of the great challenges of basic research is to translate scientific discoveries into the improved treatment of patients. For colorectal cancer, our increased understanding of the molecular aetiology of the disease has not yet been paralleled by an improvement in patient care. However, several new approaches are on the verge of clinical implementation. Technical advances such as real-time polymerase chain reaction (PCR) and microarray techniques coupled to insight in the molecular pathways in colorectal cancer makes it possible to develop new clinical tools for the diagnosis, classification and treatment of patients. The ultimate goal of the incorporation of cancer genetics into the clinical treatment of patients is individualised medicine; therapeutic strategies based on the molecular taxonomy of tumours and individually constructed for each patient.

Methods of molecular analysis: mutation detection in solid tumours

Most mutation detection techniques are unsuitable for routine use on solid tumours. Important parameters include sensitivity, specificity, efficiency, use of existing resources, and cost. In the UK, < 0.2% of service genetics laboratory activity involves mutation analysis in tumours (usually for family studies), mainly because it is time consuming/labour intensive (thus expensive) and DNA extracted from formalin fixed, paraffin wax embedded tissue is of low quality and yield. The small size of DNA fragments obtained from tissue blocks limits the polymerase chain reaction, the basis of most mutation detection methods. Other, biological, factors include: (1) heterogeneity of mutations within and between tumours, (2) variation in type and site of mutations in any one gene, (3) normal tissue harbouring mutations, (4) few genes are mutated in most of any one tumour type, and (5) few clinically useful correlations with genetic changes have been found. Present research is centred on correlating single gene mutations with various clinicopathological features, but the pattern of mutations in a combination of genes will probably prove more useful. Microsatellite instability, however, appears to be worth testing for in both familial and sporadic tumours, particularly of the colorectum.

Molecular markers in prognosis of colorectal cancer and prediction of response to treatment

Colorectal cancer is the third most common human malignancy. Direct observation and biopsy sampling by colonoscopy have provided unique opportunities to study the natural history of the disease. As a consequence, advances in the understanding of colorectal cancer pathogenesis have evolved more rapidly than with most other solid tumours. Numerous molecular events arising during the development of colorectal cancer have been sorted out over the past two decades. Despite these advances, predicting outcome and response to therapy is still a major challenge in the management of patients with colorectal cancer. Molecular and biochemical markers of colorectal cancer are greatly needed for diagnosis and prognosis as well as for the selection and monitoring of treatments. The purpose of this chapter is to provide a critical assessment of the usefulness of markers in the prognosis and prediction of response to treatment in colorectal cancer.

An endonuclease/ligase based mutation scanning method especially suited for analysis of neoplastic tissue

Knowledge of inherited and sporadic mutations in known and candidate cancer genes may influence clinical decisions. We have developed a mutation scanning method that combines thermostable EndonucleaseV (Endo V) and DNA ligase. Variant and wild-type PCR amplicons are generated using fluorescently labeled primers, and heteroduplexed. Thermotoga maritima (Tma) EndoV recognizes and primarily cleaves heteroduplex DNA one base 3' to the mismatch, as well as nicking matched DNA at low levels. Thermus species (Tsp.) AK16D DNA ligase reseals the background nicks to create a highly sensitive and specific assay. The fragment mobility on a DNA sequencing gel reveals the approximate position of the mutation. This method identified 31/35 and 8/8 unique point mutations and insertions/deletions, respectively, in the p53, VHL, K-ras, APC, BRCA1, and BRCA2 genes. The method has the sensitivity to detect K-ras mutations diluted 1 : 20 with wild-type DNA, a p53 mutation in a 1.7 kb amplicon, and unknown p53 mutations in pooled DNA samples. EndoV/Ligase mutation scanning combined with PCR/LDR/Universal array proved superior to automated DNA sequencing for detecting p53 mutations in colon tumors. This technique is well suited for scanning low-frequency mutations in pooled samples and for analysing tumor DNA containing a minority of the unknown mutation.

p53 expression in human rectal tissue after radiotherapy: upregulation in normal mucosa versus functional loss in rectal carcinomas

PURPOSE

In vitro, ionizing radiation of epithelial cells leads to upregulation of wild-type p53 and subsequent induction of p21(waf1). The effect of radiotherapy (RT) on the expression of these proteins in patients is unknown. We assessed the influence of RT on the expression of p53 and p21(waf1) in normal mucosa and rectal carcinomas in vivo.

METHODS

Tumor and normal tissue samples were derived from rectal cancer patients randomized in a clinical trial in which the value of preoperative RT was evaluated. p53 and p21(waf1) expression was determined in 51 irradiated and 52 nonirradiated patients using immunohistochemistry.

RESULTS

In normal mucosa, both p53 and p21(waf1) were strongly upregulated after RT compared with the expression in unirradiated normal tissue (p <0.001). In tumor cells, no significant difference in the expression of p53 or p21(waf1) was found in the irradiated vs. nonirradiated group. In the few rectal tumors with wild-type p53, induction of p53 after RT did not necessarily lead to upregulation of p21(waf1).

CONCLUSION

These findings demonstrate that in normal mucosa, a functional p53-p21(waf1) pathway is present, whereas in tumor cells it is defective in almost all cases because of either p53 mutation or down- or upstream disruption in tumors with wild-type p53. Therefore, we believe that the role of p53 expression as a single prognostic marker in rectal cancer needs reconsideration.

P53 overexpression predicts poor chemosensitivity to high-dose 5-fluorouracil plus leucovorin chemotherapy for stage IV colorectal cancers after palliative bowel resection

Our study aims to further clarify the prognostic significance of p53 overexpression in stage IV colorectal cancer. Between January 1994 and June 1997, we recruited 144 patients with stage IV colorectal cancers for our study, based on appropriate eligibility criteria. The patients were nonrandomly allocated to 2 treatment groups of either with or without high-dose 5-fluorouracil plus leucovorin chemotherapy (HDFL: 5-Fu: 2,600 mg/m(2) leucovorin 300 mg/m maximum 500 mg). Each treatment group was further divided into 2 subgroups according to the status of p53 overexpression. Therefore, 4 subgroups were allocated in our study and were designated as p53 (overexpression) HDFL (+), n = 65; p53 (normal) HDFL (+), n = 37; p53 (overexpression) HDFL (-), n = 27; and p53 (normal) HDFL (-), n = 15, respectively. All patients were prospectively followed until April 2001. There was no significant difference of the background clinicopathologic data of these 4 allocated subgroups of patients (p > 0.05). Multivariate analysis of various clinicopathologic factors of the whole group of patients indicated that age > or = 60 years, poor differentiation, mucin production, CEA > 100 ng/ml, p53 overexpression and without chemotherapy were the significant independent poor prognostic factors (p < 0.05). Survival analyses indicated that the patients of subgroup p53 (normal) HDFL (+) survived significantly longer than those of subgroup p53 (overexpression) HDFL (+), with mean survival time (95% confidence interval [CI]) of 20.24 (16.24-24.25) and 13.29 (10.98-15.60) months, respectively (p = 0.0043, log-rank test). In contrast, in patients without chemotherapy, the prognosis was poor regardless of their p53 status, with mean survival time (95% CI) of 6.85 (5.47-8.23) and 5.87 (4.48-7.26) months in p53 (overexpression) HDFL (-) and p53 (normal) HDFL (-) subgroups of patients, respectively (p = 0.2820, log-rank test). Cancers of normal p53 expression responded significantly better to HDFL (p < 0.05), with mean response rate (95% CI) being 65.57% (52.18-82.96%) in subgroup p53 (normal) HDFL (+) as compared to 35.38% (23.52-47.24%) in subgroup p53 (overexpression) HDFL (+). The toxicity to HDFL was similarly minimal between p53-normal and p53-overexpression patients (p > 0.05). We thus concluded that the poorer prognosis of stage IV colorectal cancers with p53 overexpression was associated with their poorer chemosensitivity rather than the more biologic aggressiveness.

Expression and prognostic significance of O6-methylguanine-DNA methyltransferase in hepatocellular, gastric, and breast cancers

BACKGROUND

O6-Methylguanine-DNA methyltransferase (MGMT) is an enzyme that repairs O6-methylguanine, a promutagenic DNA base damaged by endogenous and environmental alkylating agents. There are few reports that describe whether or not abnormal MGMT expression correlates with the prognosis in human solid cancers.

METHODS

The expression of MGMT was immunohistochemically evaluated in 60, 62, 105, and 46 paraffin-embedded samples from patients with curatively resected hepatocellular, gastric, colorectal, and breast cancers, respectively.

RESULTS

The expression of MGMT was a positive predictive factor for overall survival in hepatocellular (P = .005) and gastric cancers (P < .001) and for relapse-free survival in breast cancers (P < .001). MGMT-positive gastric tumors (n = 42) were correlated with the absence of serosal invasion (P = .045), lymph node metastasis (P = .006), intestinal type (P = .018), and low pathological tumor, node, metastasis stage (P < .001). All breast tumors that recurred locally after operation were MGMT negative (P = .004). The clinicopathologic characteristics of colorectal cancers with respect to MGMT expression did not significantly differ.

CONCLUSIONS

The expression of MGMT is a predictive prognostic marker in patients with hepatocellular, gastric, and breast cancers. These findings may help to establish therapeutic strategies for patients with these types of solid cancer.

Lifestyle factors and Ki-ras mutations in colon cancer tumors

Heterogeneity in colon tumors implies that environmental, lifestyle, or genetic factors influence the type of mutations seen in tumors. In this study we evaluate the association between previously identified risk factors for colon cancer and Kirsten-ras (Ki-ras) mutations in tumors. The presence of Ki-ras mutations in codons 12 and 13 were determined in a population-based case-control study of colon cancer. Participants were between 30 and 79 years of age at time of diagnosis and include both men and women. Questionnaire data were used to obtain information on lifestyle factors. Valid study data and Ki-ras mutational status were available from 1428 cases of colon cancer, data from 2410 controls were available for comparative purposes. Participants with Ki-ras mutations were more likely to have proximal rather than distal tumors. Cigarette smoking, use of aspirin and/or NSAIDs, use of vitamin/mineral supplements, and consumption of caffeine were associated with both Ki-ras+ and Ki-ras- tumors; the associations were not confounded by dietary intake or other lifestyle factors. Among men, but not among women, those with low levels of physical activity were more likely to have a tumor with a Ki-ras mutation than one without a Ki-ras mutation. However, among women, those with a larger BMI were more likely to have a Ki-ras mutation in their tumor. Given the limited information available on what causes Ki-ras mutations, the information generated from this study indicates that these factors previously associated with colon cancer work through other disease pathways.

Methylation and colorectal cancer

Statistics rate colorectal adenocarcinoma as the most common cause of cancer death on exclusion of smoking-related neoplasia. However, the reported accumulation of genetic lesions over the adenoma to adenocarcinoma sequence cannot wholly account for the neoplastic phenotype. Recently, heritable, epigenetic changes in DNA methylation, in association with a repressive chromatin structure, have been identified as critical determinants of tumour progression. Indeed, the transcriptional silencing of both established and novel tumour suppressor genes has been attributed to the aberrant cytosine methylation of promoter-region CpG islands. This review aims to set these epigenetic changes within the context of the colorectal adenoma to adenocarcinoma sequence. The role of cytosine methylation in physiological and pathological gene silencing is discussed and the events behind aberrant cytosine methylation in ageing and cancer are appraised. Emphasis is placed on the interrelationships between epigenetic and genetic lesions and the manner in which they cooperate to define a CpG island methylator phenotype at an early stage in tumourigenesis. Finally, the applications of epigenetics to molecular pathology and patient diagnosis and treatment are reviewed.

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.

p53 and K-ras mutations in pancreatic juice samples from patients with chronic pancreatitis

BACKGROUND

Mutations in p53 and ras genes are frequent in pancreatic carcinoma. Several ras mutations are consistently detected in the pancreatic juice from patients with chronic pancreatitis. The p53 gene mutations have been detected occasionally in chronic pancreatitis tissue. It was the aim of this study to evaluate the presence and clinical significance of p53 and ras mutations in clinical pancreatic juice samples from patients with chronic pancreatitis.

METHODS

Pancreatic juice was obtained from 66 patients with chronic pancreatitis and no evidence of pancreatic carcinoma (51 men, 15 women; age 17-86 years [mean 49.6 +/- 12.9]). Patients were followed prospectively for 26 +/- 3 (4-54) months. Detection of p53 gene mutations was by temperature gradient gel electrophoresis (TGGE) and single strand conformation polymorphism (SSCP) for exons 5-8. Analysis of ras mutations was performed by SSCP/polymerase chain reaction, restriction fragment length polymorphism/polymerase chain reaction. All mutations were confirmed by sequencing.

RESULTS

Five of 66 (7.5%) pancreatic juice samples contained p53 mutations, and ras mutations were detected in 6 cases (9%). Cytology was negative in all cases. No pancreatic carcinoma developed during follow-up and neither cancer cells nor preneoplastic lesions could be detected histologically in resected specimens. Although no correlation between p53 mutations and duration of pancreatitis or drinking habits was found, K-ras mutations correlated with both heavy smoking and severity of the disease.

CONCLUSION

p53 and ras mutations can be detected in a minority of pancreatic juice samples from patients with chronic pancreatitis in the absence of malignancy.

Clinical significance of K-Ras mutations in intraoperative tumor drainage blood from patients with colorectal carcinoma

BACKGROUND

Recurrent and metastatic carcinoma of the colorectum remains a major problem. This may be ascribed to the presence of micrometastasis at diagnosis. The purpose of this study was to analyze prospectively the clinical value of detecting K-ras mutations in the perioperative circulating blood from patients with colorectal carcinoma.

METHODS

Twenty-four patients whose tumor carried mutations in codon 12 of the K-ras gene were studied for the presence of cancer cells in perioperative blood samples, in particular, tumor drainage samples. A detection assay using CD45 immunomagnetic separation plus nested mutant allele specific amplification (MASA) was performed.

RESULTS

K-ras mutations in CD45 negative cells in tumor drainage blood were detected in 7 (29.2%) of 24 patients. There was no significant relationship between the presence of a K-ras mutation and clinicopathological features. Four (57.1%) of the seven patients with a positive K-ras mutation in drainage blood had early recurrent disease. Of the 17 patients with no K-ras mutation, none developed metastatic disease. The recurrence rate of the K-ras mutation positive group was higher than that of the K-ras mutation negative group (P < .01). There was a significant difference, regarding prognosis, between K-ras mutation positive and negative groups (P < .01).

CONCLUSIONS

This preliminary study demonstrates that the detection of circulating cancer cells in the tumor drainage blood by our new assay system may provide a predictor of recurrence and metastasis of colorectal cancer.

Determination of microsatellite instability, p53 and K-RAS mutations in hepatic metastases from patients with colorectal cancer: relationship with response to 5-fluorouracil and survival

In vitro and clinical studies have suggested that high-frequency microsatellite instability (MSI-H) phenotype, p53 and K-ras mutations might influence the response to chemotherapy in a variety of tumors, including primary colorectal cancers (CRC). Unresectable hepatic metastases from CRC are commonly treated with 5-fluorouracil (5FU) and folinic acid. Since several new active drugs are now used for treating CRC, molecular determinants predictive to response to 5FU would thus be crucial for optimizing indications of chemotherapy to those patients. MSI-H phenotype, p53 and K-ras status were characterized in a prospective study of 56 patients with CRC metastatic to the liver and treated with 5FU-based chemotherapy. The objective response rate after a 3-month treatment was 32.1%. The prevalence of p53 mutations, K-ras mutations and MSI-H phenotype was 62.5%, 30.3% and 1.8%, respectively. No significant association was found between response to chemotherapy and p53 mutations (78% mutated tumors in responders vs. 55% in nonresponders; p = 0.10) and K-ras mutations (39% mutated tumors in responders vs. 26% in nonresponders; p = 0.34). Survival was longer for patients with p53-mutated metastases than for patients with unresected wild-type p53 metastases (median survival 15 months vs. 17 months; p = 0.06). The determination of the MSI-H phenotype, p53 and K-ras status in hepatic metastases from CRC does not discriminate a group of patients that should preferentially benefit from 5FU-based chemotherapy. The prognosis of patients with treated liver metastases is better when p53 is mutated.

The results of colorectal cancer treatment by p53 status: treatment-specific overview

PURPOSE

Both negative and positive influences of mutant p53 on treatment outcome have been reported, and we present here a meta-analysis of published studies where outcome was reported for defined treatment groups.

METHODS

We identified articles on the effect of p53 status by treatment modality, excluding those not stratified by method of treatment. A common hazard ratio was estimated from studies that reported a multivariate analysis. We also estimated the numbers of patients expressing the endpoint at the mean or median follow-up time and calculated a pooled odds ratio.

RESULTS

Twenty-eight articles were evaluable (23 using immunohistochemistry to detect overexpression of p53 and 8 using DNA sequencing), for a total of 4,416 patients. For patients treated with surgery only, the immunohistochemistry studies showed a significant influence of p53 status on disease-free survival and a marginally significant influence on overall survival. In the studies using DNA sequencing, by contrast, there was a significant influence of p53 mutations on overall survival, but not disease-free survival. For patients treated with surgery and radiotherapy, the influence of p53 status on disease-free survival was either insignificant or marginally significant, depending on test used; there was no influence on overall survival.

CONCLUSIONS

Although this pooled analysis of published studies where treatment was accounted for shows that there is a borderline significant hazard associated with p53 overexpression or mutation vs. p53 wild-type, it is unlikely that p53 can be applied in a routine clinical setting alongside factors such as T stage, nodal status, and residual tumor, whose prognostic value is much stronger.

Redefining the significance of aneuploidy in the prognostic assessment of colorectal cancer

The aberrant content of DNA, or aneuploidy, is a hallmark of tumor cells and may be associated with malignant potential. Based on the hypothesis that aneuploidy, as a form of genetic instability, results in an increased capability to generate cell heterogeneity, we investigated whether a comprehensive assessment of aneuploidy extent and degree might be a reliable indicator of tumor aggressiveness. DNA content was determined by flow cytometry in the infiltrating front of 131 paraffin-embedded primary colorectal carcinomas collected in a prospective design. Enrichment of tumor cells by sample microdissection resulted in neoplastic cell contents above 75%. An estimate of aneuploidy, the aneuploidy index (AI), was calculated as the tumor DNA content adjusted by the percentage of diploid and aneuploid cells in G0/G1. Thirty-nine tumors were diploid, 90 hyperdiploid, and 2 hypodiploid. The mean AI in aneuploid tumors was 1.20+/-0.17 and correlated with Dukes' stage and metastasis (p < 0.05). A high AI (receiver operating characteristic curve cutoff value greater than 1.14) predicted a poorer outcome in univariate (p = 0.004) and multivariate (p = 0.01) analyses. Based on these results, we postulate that aneuploidy is the molecular engine of progression in a subset of colorectal cancers, in which the AI seems to be a sensible and independent gauge of malignant potential. The AI determination may have prognostic application in colorectal cancer, especially in low-grade tumors, which might benefit from coadjuvant therapies.

Relevance of Ki-67 antigen expression and K-ras mutation in colorectal liver metastases

AIMS

The liver is a frequent site of metastases from colorectal cancer. While these lesions are potentially amenable to surgical resection, they are usually very aggressive, and recurrence is frequent. Mutations of the proto-oncogene K- ras are thought to impart a strong growth signal to tumour cells and are closely associated with the development of malignancies of the colon and rectum. Hepatic metastases from colorectal cancer have notably elevated proliferative rates. The present study was performed to investigate the relationship between proliferation or K- ras mutation and prognosis following curative resection of colorectal liver metastases.

METHODS

Colorectal liver metastases from 41 patients undergoing curative hepatic resection were examined for proliferation status and presence of K- ras mutations. The proliferative activity was assessed by Ki-67 immunohistochemistry. DNA from the same tissue samples was screened for point mutations in codon 12 of the K- ras gene using a novel microplate-based allelic-specific hybridization assay. Ki-67 scores and K- ras status were then related with patient survival as determined through retrospective analysis.

RESULTS

Median survival was 40 months. Patients with high Ki-67 scores (> or = 50%) had significantly shorter median survival compared with those with low scores (30 vs 44 months, log-rank P=0.02). A high Ki-67 score was an independent negative prognostic factor by multivariate regression analysis (relative risk=3.04, P=0.036). K- ras point mutations were detected in 6/41 patients (15%), but mutational status did not correlate with Ki-67 score or survival.

CONCLUSIONS

These findings suggest that the tumour proliferative index is a useful predictor of aggressive tumour behaviour and an indicator of patient survival. The presence of K- ras mutations does not appear to correlate with tumour proliferation status or patient survival.

K-ras and p16 aberrations confer poor prognosis in human colorectal cancer

PURPOSE

Mutations in the K-ras gene are frequent in human cancer. ras activation in primary cells results in a cellular senescence phenotype that is precluded by inactivation of p16. At the clinical level, this may imply a differential behavior for tumors with alternative or cooperative activation of K-ras function and impairment of p16 pathways.

PATIENTS AND METHODS

We have determined the presence of mutations in the K-ras gene and the methylation status of p16 promoter in a series of 119 prospectively collected colorectal carcinomas. p53 mutations and p14 alternative reading frame methylation status were also assessed. Associations with survival were investigated.

RESULTS

K-ras mutations were present in 44 (38%) of 115 cases, and p16 methylation was present in 42 (37%) of 113 cases. p53 mutations were detected in 50% (56 of 115) and p14 methylation in 29% (32 of 112) of cases. K-ras and p16 alterations were independent genetic events. Presence of K-ras or p16 genetic alterations (analyzed independently) was associated with shorter survival, although differences were not statistically significant. Cox analysis of the two variables combined showed a diminished survival as the results of an interaction between p16 and K-ras. Alternative alteration of K-ras and p16 genes was an independent prognostic factor in human colorectal cancer in univariate and multivariate analysis. Differences were maintained when cases undergoing radical surgery and without distant metastases were considered.

CONCLUSION

These results suggest that the combined K-ras and p16 analyses may be of prognostic use in human colorectal cancer.

Lack of prognostic significance of p53 and K-ras mutations in primary resected non-small-cell lung cancer on E4592: a Laboratory Ancillary Study on an Eastern Cooperative Oncology Group Prospective Randomized Trial of Postoperative Adjuvant Therapy

PURPOSE

To determine the prognostic and predictive significance of p53 and K-ras mutations in patients with completely resected non-small-cell lung cancer (NSCLC).

PATIENTS AND METHODS

Patients were randomized preoperatively to receive adjuvant postoperative radiotherapy (Arm A) or radiotherapy plus concurrent chemotherapy (Arm B). p53 protein expression was studied by immunohistochemistry (IHC) and p53 mutations in exons 5 to 8 were evaluated by single-strand conformational analysis. K-ras mutations in codons 12, 13, and 61 were determined using engineered restriction fragment length polymorphisms.

RESULTS

Four hundred eighty-eight patients were entered onto E3590; 197 tumors were assessable for analysis. Neither presence nor absence of p53 mutations, p53 protein expression, or K-ras mutations correlated with survival or progression-free survival. There was a trend toward improved survival for patients with wildtype K-ras (median, 42 months) compared with survival of patients with mutant K-ras who were randomized to chemotherapy plus radiotherapy (median, 25 months; P = .09). Multivariate analysis revealed only age and tumor stage to be significant prognostic factors, although there was a trend bordering on statistical significance for K-ras (P = .066). Analysis of survival difference by p53 by single-stranded conformational polymorphism and IHC, interaction of p53 and K-ras, interaction of p53 and treatment arm, nodal station, extent of surgery, weight loss, and histology did not reach statistical significance.

CONCLUSION

p53 mutations and protein overexpression are not significant prognostic or predictive factors in resected stage II or IIIA NSCLC. K-ras mutations may be a weak prognostic marker. p53 or K-ras should not be routinely used in the clinical management of these patients.

K-ras oncogene mutation in cancer and precancerous lesions of the gallbladder

BACKGROUND AND OBJECTIVES

To determine whether K-ras mutation plays any role in the development and progression of gallbladder cancer, or has any clinical or pathological significance in gallbladder cancer patients, we investigated the presence and incidence of this mutation in the normal mucosa, and precancerous and cancerous lesions of the gallbladder.

METHODS

DNA was obtained from normal mucosa, dysplastic mucosa, primary cancer tissues, and metastatic lymph nodes that were identified and microdissected from the paraffin blocks of 20 gallbladder cancer cases. K-ras codon 12 mutations were investigated using a modified two-step polymerase chain reaction and the restriction fragment length polymorphism method, and by direct sequencing with an automated sequencer.

RESULTS

K-ras mutations were detected in the tissues of 10 out of the 20 patients. A mutation was present in the dysplastic epithelium associated with the primary carcinoma in 3 out of 12 specimens, in metastatic carcinoma in 1 out of 5 patients, and in primary carcinoma in 8 out of 20 patients. Mutation was found only once in the dysplastic, noncancerous epithelium, and only once in a metastatic tumor although not detectable in the primary cancer. Direct sequencing showed that the mutations were G to C substitutions (GGT-->CGT) at the first site of codon 12, except in two cases (GGT-->TGT). There were no correlations between K-ras mutations and clinicopathological factors.

CONCLUSIONS

K-ras mutations were detected in half of the gallbladder cancer cases. We suggest that K-ras mutation may play a role in the development of premalignant lesions or early carcinogenesis in some gallbladder cancers. We were unable to find any evidence that K-ras mutation plays any role in tumor progression or metastasis, or that it has any clinicopathological significance.