Detection of c-Ki-ras mutations in faecal samples from sporadic colorectal cancer patients

Demethylation of the HACE1 gene promoter inhibits the proliferation of human liver cancer cells

HECT domain and ankyrin repeat containing E3 ubiquitin protein ligase 1 (HACE1) is frequently downregulated or lost in numerous types of cancer, including liver cancer. The aim of the present study was to examine whether demethylation of the HACE1 gene could inhibit tumour progression. The expression of HACE1 was detected in liver cancer cell lines. Clustered regularly interspaced short palindromic repeats (CRISPR)-CRISPR-associated (Cas)-based demethylation single guide RNAs for the HACE1 gene promoter were designed and transfected into liver cancer cells. Subsequently, proliferation was detected by MTT and colony formation assays, and optineurin (OPTN) ubiquitination and microtubule-associated proteins 1A/1B light chain 3B protein levels were detected by immunoblotting. The levels of HACE1 were significantly reduced in liver cancer cell lines compared with in a normal liver cell line. Demethylation of the HACE1 gene promoter increased HACE1 expression, inhibited the proliferation of liver cancer cells, and promoted OPTN ubiquitination and autophagy activity in liver cancer cells. In conclusion, activation of HACE1 expression by promoter demethylation may provide a suitable approach for anticancer therapy.

Molecular Detection of Codon 12 K-RAS Mutations in Circulating DNA from Serum of Colorectal Cancer Patients

Point mutations of the K-RAS gene at codon 12 are found in about 40% of cases with colorectal cancer. The diagnostic implications of the detection of these mutations and their clinical utility are still unclear. The aim of this study was to test both the feasibility of the detection of the mutated K-RAS gene in serum and its potential role in colorectal cancer detection and monitoring.

Codon 12 K-RAS mutations were examined in DNA extracted from the serum of 35 patients with colorectal cancer and were compared with the K-RAS status in the corresponding primary tumor. Molecular detection was performed by the mutant-enriched PCR (ME-PCR) assay, a sensitive method capable of distinguishing a small quantity of mutated DNA in the presence of abundant wild-type DNA. The occurrence of mutations was compared with clinicopathological parameters as well as CEA and CA19.9 serum levels.

We found codon 12 K-RAS mutations in the tissue of 13/35 (37%) patients. Serum mutations were detected in 5/13 (38.5%) patients with mutated K-RAS in the tissue. 26/35 (74%) patients showed an identical K-RAS pattern in tissue and serum. No codon 12 K-RAS alterations were found in serum samples of 22 patients with benign gastrointestinal diseases. Elevated serum CEA levels were detected in 16 patients, four of whom also presented serum RAS mutations.

Our results confirm that K-RAS mutations can be found in circulating DNA extracted from serum samples of patients with colorectal cancer and show that there is a correspondence between serum and tissue K-RAS patterns.

Consensus on the Prevention, Screening, Early Diagnosis and Treatment of Colorectal Tumors in China: Chinese Society of Gastroenterology, October 14-15, 2011, Shanghai, China

BACKGROUND

Colorectal cancer (CRC) is steadily increasing in China. Colorectal adenoma (CRA) is the most important precancerous disease of CRC. Screening for colorectal tumors can aid early diagnosis. Advances in endoscopic mucosal resection and endoscopic submucosal dissection can aid the early treatment of colorectal tumors. Furthermore, because of high risk of recurrence after removal of adenomas under endoscopy, factors contributing to recurrence, the follow-up mode and the interval established, and the feasibility of application and the time of various chemical preventions should be concerned. However, a relevant consensus on the screening, early diagnosis and treatment, and prevention of colorectal tumors in China is lacking.

SUMMARY

The consensus recommendations include epidemiology, pathology, screening, early diagnosis, endoscopic treatment, monitoring and follow-up, and chemoprevention of colorectal tumors in China.

KEY MESSAGE

This is the first consensus on the prevention, screening, early diagnosis and treatment of CRA and CRC in China based on evidence in the literature and on local data.

PRACTICAL IMPLICATIONS

Through reviewing the literature, regional data and passing the consensus by an anonymous vote, gastroenterology experts from all over China launch the consensus recommendations in Shanghai. The incidence and mortality of CRC in China has increased, and the incidence or detection rate of CRA has increased rapidly. Screening for colorectal tumors should be performed at age 50-74 years. Preliminary screening should be undertaken to find persons at high risk, followed by colonoscopy. A screening cycle of 3 years is recommended for persistent interventions. Opportunistic screening is a mode suitable for the current healthcare system and national situation. Colonoscopy combined with pathological examination is the standard method for the diagnosis of colorectal tumors. CRA removal under endoscopy can prevent CRC to some extent, but CRA has an obvious recurrence trend. The follow-up interval after the removal or surgery of colorectal tumors should be different with lesions. Primary prevention of CRA includes improved diet with more fiber, supplements containing calcium and vitamin D, supplements containing folic acid for those with low hemoglobin levels, and cessation of tobacco smoking. Non-steroidal anti-inflammatory drugs and selective cyclooxygenase-2 inhibitors have been recognized to prevent recurrence after adenoma removal.

Detection of DNA hypermethylation in remote media of patients with colorectal cancer: new biomarkers for colorectal carcinoma

Colorectal cancer is the third most common cancer and a major cause of cancer-related mortality. The lifetime risk to develop colorectal cancer is 6% in the Western world, and one third of the affected people will ultimately die from this disease. Colorectal carcinomas develop slowly over a period of several years. Therefore, identifying people with precancerous lesions holds the potential to reduce the incidence and mortality of colorectal cancer. Apart from mutations and chromosomal imbalances, inactivation of tumor suppressor genes by DNA hypermethylation has been recognized as an important mechanism driving colorectal carcinogenesis. In recent years, screening tests have been developed that rely on the detection of DNA hypermethylation in remote media to identify people suffering from asymptomatic colorectal cancers at early stages. Apart from their diagnostic value, methylation markers hold the potential to be used as prognostic markers. Here, we summarize the recent development of DNA methylation markers for colorectal cancer in remote media with regard to their diagnostic and prognostic value.

Fecal molecular markers for colorectal cancer screening

Despite multiple screening techniques, including colonoscopy, flexible sigmoidoscopy, radiological imaging, and fecal occult blood testing, colorectal cancer remains a leading cause of death. As these techniques improve, their sensitivity to detect malignant lesions is increasing; however, detection of precursor lesions remains problematic and has generated a lack of general acceptance for their widespread usage. Early detection by an accurate, noninvasive, cost-effective, simple-to-use screening technique is central to decreasing the incidence and mortality of this disease. Recent advances in the development of molecular markers in faecal specimens are encouraging for its use as a screening tool. Genetic mutations and epigenetic alterations that result from the carcinogenetic process can be detected by coprocytobiology in the colonocytes exfoliated from the lesion into the fecal matter. These markers have shown promising sensitivity and specificity in the detection of both malignant and premalignant lesions and are gaining popularity as a noninvasive technique that is representative of the entire colon. In this paper, we summarize the genetic and epigenetic fecal molecular markers that have been identified as potential targets in the screening of colorectal cancer.

Epigenomic analysis of aberrantly methylated genes in colorectal cancer identifies genes commonly affected by epigenetic alterations

BACKGROUND

Determination of the profile of genes that are commonly methylated aberrantly in colorectal cancer (CRC) will have substantial value for diagnostic and therapeutic applications. However, there is limited knowledge of the DNA methylation pattern in CRC.

MATERIALS AND METHODS

We analyzed the methylation profile of 27,578 CpG sites spanning more than 14,000 genes in CRC and in the adjacent normal mucosa with bead-chip array-based technology.

RESULTS

We identified 621 CpG sites located in promoter regions and CpG islands that were greatly hypermethylated in CRC compared to normal mucosa. The genes on chromosome 18 showed promoter hypermethylation most frequently. According to gene ontology analysis, the most common biologically relevant class of genes affected by methylation was the class associated with the cadherin signaling pathway. Compared to the genome-wide expression array, mRNA expression was more likely to be downregulated in the genes demonstrating promoter hypermethylation, even though this was not statistically significant. We validated ten CpG sites that were hypermethylated (ADHFE1, BOLL, SLC6A15, ADAMTS5, TFPI2, EYA4, NPY, TWIST1, LAMA1, GAS7) and 2 CpG sites showing hypomethylation (MAEL, SFT2D3) in CRC compared to the normal mucosa in the array studies using pyrosequencing. The methylation status measured by pyrosequencing was consistent with the methylation array data.

CONCLUSIONS

Methylation profiling based on bead-chip arrays is an effective method for screening aberrantly methylated genes in CRC. In addition, we identified novel methylated genes that are candidate diagnostic or prognostic markers for CRC.

Quantitative denaturing high performance liquid chromatography (Q-dHPLC) detection of APC long DNA in faeces from patients with colorectal cancer

BACKGROUND

Colorectal cancer (CRC) is the second leading cause of cancer-related deaths. However, prevention is possible by early detection. In the present work, we have demonstrated and validated a novel quantitative method based on a DNA integrity assay and mutation in faeces of CRC patients using denaturing high performance liquid chromatography (dHPLC).

METHODS

Faecal DNA (fDNA) was isolated from 28 CRC, 96 healthy and 61 patients with adenomas. Adenomatosis polyposis coli (APC)-Long-DNA and its mutations were analysed using dHPLC and the Sanger sequencing method. The diagnostic performance was assessed using receiver operating characteristic curve analysis.

RESULTS

We detected APC-Long-DNA in 21/28 CRC subjects with a sensitivity of 75% and specificity of 91.7%. A cut-off ratio of 0.2317 was used for APC/β-actin. The Q-dHPLC detection limit was 0.02 ng/injection. The average initial fDNA presence based on a single gene of β-actin was 26.12 ± 13.39 ng/mL for healthy, and 49.61 ± 46.28 ng/mL for CRC subjects, with a sensitivity of 71.4% and a specificity of 84.4% at a cut-off value >29 ng/mL. We also detected a novel mutation at codon 1576 Lys/Glu using dHPLC.

CONCLUSIONS

This study highlights a novel application of Q-dHPLC in the DNA integrity assay, which demonstrates high performance, good reproducibility, and low cost for the CRC detection using faeces. Further studies in a larger population are needed to confirm these results.

The role of oncogenes in gastrointestinal cancer

Oncogene research over the last century has been one of the major advances in understanding the molecular biology of malignant disease. Oncogenes are a structurally and functionally heterogeneous group of genes, whose protein products act pleiotropically and affect multiple complex regulatory cascades within the cell. They regulate cell proliferation, growth, and differentiation, as well as control of the cell cycle and apoptosis. The products of oncogenes include growth factors, growth factor receptors, signal transducers, transcription factors, and apoptosis regulators, as well as chromatin remodelers. Several distinct mechanisms have been described for the conversion of proto-oncogenes to active oncogenes. Quantitative forms of oncogene activation include multiplication (gene amplification) or translocation to an active chromatin domain that brings a growth-regulatory gene under the control of a different promoter, causing inappropriate expression of the gene. Qualitative forms include either point mutations or the production of a novel product from a chimeric gene. Further understanding of the molecular mechanisms by which oncogenes regulate normal development and tumorigenesis may lead to novel concepts in the diagnosis and treatment of cancer in humans. In this review, we focus on the role of selected oncogenes in gastrointestinal cancer.

Murine fecal proteomics: a model system for the detection of potential biomarkers for colorectal cancer

Tumor related products shed into the feces offer a potential source of biomarkers for the detection of colorectal cancer (CRC). Using SDS-PAGE followed by nanoflow reversed-phased LC-MS/MS to analyse fecal samples from Apc(Min/+) mice (that develop spontaneous multiple intestinal neoplasia with age) we have identified 336 proteins (115 proteins of murine origin, 201 from fecal bacteria, 18 associated with food intake and 2 of apparent parasitic origin). 75% of the murine proteins identified in this study are predicted to be extracellular or associated with the cell plasma membrane. Of these proteins, a number of the murine homologues of colorectal cancer associated proteins (CCAP) such as hemoglobin, haptoglobin, hemopexin, alpha-2-macroglobulin and cadherin-17 have been identified, demonstrating the potential of fecal proteomics for detecting potential biomarkers and paving the way for subsequent MS/MS based biomarker studies on similar human samples.

Metabolite profiling of fecal water extracts from human colorectal cancer

Colorectal cancer is the second leading cause of cancer death in developed countries. There is a need for better preventive strategies to improve the outcome of this disease. The increasing availability of high-throughput methodologies opens up new possibilities for screening new markers. The application of NMR metabolic profiling to fecal water extracts has interesting potential as a diagnostic tool for detecting colorectal cancer. We obtained NMR metabolic profiles of fecal water extracts from patients with colorectal cancer and healthy individuals, to characterize possible differences between them and to identify potential diagnostic markers. Our results show that metabolic profiling of fecal water extracts is a cheap, reproducible and effective method for detecting colorectal cancer markers and therefore complements other stool-screening methods. A low concentration of short-chain fatty acids, such as acetate and butyrate, previously associated with the development of colorectal cancer, appears to be the most effective marker. Concentrations of proline and cysteine, which are major components of most colonic epithelium mucus glycoproteins, also display significant changes in samples from colorectal cancer. Differentiation between fecal water extracts from controls and patients with colorectal cancer by NMR spectroscopy combined with chemometric techniques opens up new possibilities for developing new, efficient, high-throughput screening protocols.

High detection rates of colorectal neoplasia by stool DNA testing with a novel digital melt curve assay

BACKGROUND & AIMS

Current stool DNA tests identify about half of individuals with colorectal cancers and miss most individuals with advanced adenomas. We developed a digital melt curve (DMC) assay to quantify low-abundance mutations in stool samples for detection of colorectal neoplasms and compared this test with other approaches.

METHODS

We combined a melt curve assay with digital polymerase chain reaction and validated the quantitative range. We then evaluated its ability to detect neoplasms in 2 clinical studies. In study I, stool samples from patients with colorectal tumors with known mutations (KRAS, APC, BRAF, TP53) were assayed. In study II, archived stool samples from patients with advanced adenomas containing known KRAS mutations were assayed, along with controls. Results were compared with those from the stool DNA test PreGenPlus (Exact Sciences, Marlborough, MA), Hemoccult, and HemoccultSensa (both Beckman-Coulter, Fullerton, CA).

RESULTS

The DMC assay detected samples in which only 0.1% of target genes were mutated. In study I, the DMC assay detected known mutations in 28 (90%) of 31 tumor samples and 6 (75%) of 8 advanced adenoma samples. In study II, the DMC assay detected 16 (59%) of 27 advanced adenoma samples that contained KRAS mutations, compared with 7% with the Hemoccult, 15% with the HemoccultSensa, and 26% with the PreGenPlus assays (P < .05 for each, compared with the DMC assay); specificities did not differ significantly.

CONCLUSIONS

The DMC assay has a high level of sensitivity in detecting individuals with colon neoplasms and is better than current stool screening methods in detecting those with advanced adenomas. Further studies are indicated.

Improved recovery of exfoliated colonocytes from feces using newly developed immunomagnetic beads

We demonstrated the feasibility of a new methodology for isolating colonocytes from feces. To reduce costs and improve the recovery rate of colonocytes from feces, we attempted to develop new immunomagnetic beads. Several sizes of magnetic beads were prepared and tagged with a monoclonal antibody against EpCAM. We made several new monoclonal antibodies against EpCAM, and each monoclonal antibody was tagged to the magnetic beads. In the simulation, the most efficient recovery of HT-29 cells was obtained using the smallest size of beads. Also, beads tagged with a monoclonal antibody with a higher affinity against EpCAM had a higher recovery rate. Similar results were obtained when the smallest size of beads with the highest-affinity monoclonal antibody was applied to clinical samples. The newly developed immunomagnetic beads may be useful for isolating colorectal cancer cells from feces, enabling the cytological or molecular biological diagnosis of CRC.

Biomarkers, regerons, and pathways to lethal cancer

Cancer is a disease of "outlaw" cells that become mutated in regulatory mechanisms. They have lost normal self controls and relationships to the whole organism. Cancers can progress by several pathways from a normal cell to malignant cancer, from bad to worse. Questions about advisability of treatment for some cancers arise from the possibility that they are arrested during progression and so never become lethal. Techniques could be developed to determine the degree of progression and possibility for successful treatment. This article is intended to suggest a way of looking at cancer. It is not a review so references to research articles are infrequent.

A new method for isolating colonocytes from naturally evacuated feces and its clinical application to colorectal cancer diagnosis

BACKGROUND & AIMS

The early detection of colorectal cancer is desired because this cancer can be cured surgically if diagnosed early. The purpose of the present study was to determine the feasibility of a new methodology for isolating colonocytes from naturally evacuated feces, followed by cytology or molecular biology of the colonocytes to detect colorectal cancer originating from any part of the colorectum.

METHODS

Several simulation studies were conducted to establish the optimal methods for retrieving colonocytes from any portion of feces. Colonocytes exfoliated into feces, which had been retrieved from 116 patients with colorectal cancer and 83 healthy volunteers, were analyzed. Part of the exfoliated colonocytes was examined cytologically, whereas the remainder was subjected to DNA analysis. The extracted DNA was examined for mutations of the APC, K-ras, and p53 genes using direct sequence analysis and was also subjected to microsatellite instability (MSI) analysis.

RESULTS

In the DNA analysis, the overall sensitivity and specificity were 71% (82 of 116) of patients with colorectal cancer and 88% (73 of 83) of healthy volunteers. The sensitivity for Dukes A and B was 72% (44 of 61). Furthermore, the sensitivity for cancers on the right side of the colon was 57% (20 of 35). The detection rate for genetic alterations using our methodology was 86% (80 of 93) when the analysis was limited to cases in which genetic alterations were present in the cancer tissue.

CONCLUSIONS

We have developed a new methodology for isolating colonocytes from feces. The present study describes a promising procedure for future clinical evaluations and the early detection of colorectal cancers, including right-side colon cancer.

Exfoliated colonic epithelial cells: surrogate targets for evaluation of bioactive food components in cancer prevention

There is significant evidence supporting the hypotheses that lifestyle, diet, and bioactive components in foods are important modifiers of cancer risk. However, our ability to assess host response noninvasively is limited. To overcome this, we have developed a technology to isolate several million viable exfoliated somatic colonic cells from a small sample of stool (0.5-1.0 g) by a procedure known as somatic cell sampling and recovery (SCSR). Orally administered carotenoids appear in these cells several days after consuming the supplement, usually showing a peak concentration between 5-7 d after their ingestion. The time lag observed for the appearance of orally administered carotenoids in SCSR cells corresponds to the turnover rate of the colonic mucosa. This is an example of how changes in cell turnover rates can be carefully assessed using the SCSR system. The specific mechanisms by which individual constituents of diet affect the cancer process are not fully understood. However, host response to dietary constituents may be investigated, noninvasively, by following the modulation of tumor-associated molecular markers in these exfoliated SCSR cells. We have demonstrated the feasibility of using SCSR cells to detect the expression of carcinoembryonic antigen, CD44, and its splice variants, c-myc, c-erbb2, and mutations in the p53 gene. In this regard, SCSR cells are a readily available surrogate cellular target that may serve to monitor changes in cell turnover, differentiation, and expression of cancer-associated biomarkers that are likely to be modulated by bioactive food components.

Clinical usefulness of telomerase for the detection of colon cancer in ulcerative colitis patients

BACKGROUND AND AIM

Colorectal carcinoma (CRC) is a complication of ulcerative colitis (UC). Although stool occult blood and colonoscopy are used to detect CRC in UC, these methods have drawbacks, in that bleeding is associated with UC and the underlying mucosa is irregular, making it difficult to detect dysplasia. Telomerase and its catalytic subunit, telomerase reverse transcriptase (hTERT), are specifically expressed in cancers, making them candidate markers for the early detection of cancer. We previously reported that assays of telomerase in pancreatic juice may be useful for the early detection of pancreatic cancer. The aims of our study were to determine whether assays for telomerase and TERT may be useful in the diagnosis of CRC developed in UC patients.

METHODS

Luminal washings and biopsies were collected during colonoscopy in 66 patients; 34 with CRC, 21 with UC, and 11 controls. Telomerase activity was detected by telomeric repeat amplification protocol (TRAP) and hTERT mRNA was assayed by reverse transcription-polymerase chain reaction (RT-PCR).

RESULTS

Telomerase activity was detected in biopsies from 33 of 34 (97%) CRC patients, 14 of 21 (67%) UC patients, and three of 11 (27%) normal controls. Expression of hTERT mRNA was observed in biopsies from 32 of 34 (94%) CRC patients, 12 of 21 (57%) UC patients, and five of 11 (45%) controls. In analyses of washing fluid, 21 of 34 (62%) of CRC patients were positive for telomerase, but all UC patients and controls were negative. The sensitivity of telomerase for CRC was 97% in tissues and 62% in washing fluid. The specificity of telomerase in washing fluid was 100%, whereas the specificity of telomerase or hTERT mRNA in tissues was 47% each.

CONCLUSIONS

For the detection of CRC arising in UC, telomerase and hTERT in colonic tissue showed high sensitivity, and telomerase in colonoscopic luminal washings revealed a high specificity. These might be candidate markers in clinical decision making for the diagnosis of CRC from UC.

Potential of faecal RNA in diagnosing colorectal cancer

Early diagnosis for colorectal cancer (CRC) by monitoring of gastrointestinal epithelial cells is a possible direct approach. Although human faeces form a heterogeneous mixture of gastrointestinal mucosal epithelial cells and other materials, we have developed a method to purify total RNA from human stool samples. The gene for faecal cytokeratin 19 (CK19) was highly expressed in stools from patients with metastatic CRC, but not from patients with non-metastatic CRC or from normal individuals. Thus, purified faecal RNA can be used for the detection of differentially expressed genes. This technique may help identifying meaningful faecal RNA markers for the non-invasive screening of patients with CRC.

Detection of colorectal cancer by a quantitative fluorescence determination of DNA amplification in stool

DNA amplification of exfoliated cells in stool represents an inexpensive and rapid test, but has only 50% to 60% sensitivity. A new quantitative method, called fluorescence long DNA, was developed and validated in our laboratory on stool obtained from 86 patients with primary colorectal cancer and from 62 healthy individuals. It consists of the amplification of stool DNA with fluorescence primers and the quantification of the amplification using a standard curve. Results are arbitrarily expressed in nanograms. The potential of the new method compared to the conventional approach was analyzed in a subgroup of 94 individuals (56 patients and 38 healthy volunteers). In the present series, DNA amplification analysis showed a specificity of 97% and a sensitivity of only 50%. Conversely, fluorescence DNA evaluation, using the best cutoff of 25 ng, showed a sensitivity of about 76% and a specificity of 93%. Similar sensitivity was observed regardless of Dukes stage, tumor location, and size, thus also permitting the detection of early-stage tumors. The present study seems to indicate that quantitative fluorescence DNA determination in stool successfully identifies colorectal cancer patients with a sensitivity comparable, if not superior, to that of multiple gene analysis but at a lower cost and in a shorter time.

Analysis of promoter methylation in stool: a novel method for the detection of colorectal cancer

BACKGROUND & AIMS

Detection of tumor-derived DNA alterations in stool is an intriguing new approach with high potential for the noninvasive detection of colorectal cancer (CRC). Because of heterogeneity of tumors, usually multiple markers distributed throughout the human genome need to be analyzed. This is labor intensive and does not allow for high through-put screening. Therefore, markers with high sensitivity and good specificity are needed. We explored the potential of a single epigenetic marker in comparison with fecal occult blood testing (FOBT) for the discrimination of patients with CRCs and adenomas from those without.

METHODS

Methylation-specific polymerase chain reaction (PCR) was performed to analyze hypermethylated in cancer 1 (HIC1) promoter methylation status in a blinded fashion in stool samples from 26 patients with CRC, 13 with adenoma > or =1 cm, 9 with hyperplastic polyps, 9 with chronic inflammatory bowel disease, and 32 with endoscopically normal colon.

RESULTS

Ninety-seven percent of the stool samples contained amplifiable DNA. Forty-two percent of the samples from patients with CRC and 31% of the samples from patients with colorectal adenoma > or =1 cm were positive for HIC1 promoter methylation. No methylated HIC1 promoter DNA was detected in the fecal DNA from patients with endoscopically normal colon or hyperplastic polyps.

CONCLUSIONS

The epigenetic marker HIC1 promoter methylation carries high potential for the remote detection of CRCs. We postulate that a panel of merely a few genetic and epigenetic markers will be required for the highly sensitive and specific detection of CRCs and adenomas in fecal samples from affected patients.

Stool screening for colorectal cancer: molecular approaches

Assay of molecular markers in stool represents a promising noninvasive approach to screen colorectal cancer. Given that neoplasms exfoliate abundantly into the lumen and that DNA recovered from stool can be assayed with sensitive techniques, there is a strong biologic rationale to pursue this emerging technology. A challenge with DNA-based testing relates to the selection of markers. Because of the molecular heterogeneity of cancer, no single marker has yielded perfect sensitivity. Several combinations of markers in early stool assays have produced high detection rates of both colorectal cancer and advanced adenomas in selected patient groups, but observations from large representative populations are lacking at present. Potential expanded applications of stool DNA testing include detection of supracolonic aerodigestive cancers and of dysplasia in inflammatory bowel disease. Further marker discovery and technologic refinements should translate into improved test performance and fuel a continued evolution with this screening approach.

Molecular stool screening for colorectal cancer

BACKGROUND

Mass screening for colorectal cancer reduces mortality and, with recent advances in molecular genetics, molecular stool-based tests have produced promising results. This article reviews this innovation and discusses its clinical significance.

METHODS

Medline searches were used to identify recent key articles relating to stool-based testing. Further articles were obtained by manual scanning of the reference lists of identified papers.

RESULTS

Current screening methods are based on endoscopic, radiological and stool-based testing. Recent recognition of the adenoma-carcinoma sequence and pathophysiological studies of colonic epithelium have enabled tumour markers to be used in the screening setting. Non-invasive molecular stool testing has now been shown to have a high sensitivity and specificity.

CONCLUSION

Recent studies on molecular stool-based testing have shown higher sensitivity and specificity than earlier studies, but larger clinical trials are required. Laboratory methods are still undergoing research, with the aim of improving sensitivity to allow large-scale testing.

The evolution to stool DNA testing for colorectal cancer

Despite a variety of screening strategies and recent trends showing death rate stabilization, colorectal cancer still remains the second leading cause of overall cancer death. Current screening tools suffer from performance limitations, low patient acceptability, and marginal reliable access within the health care system. Noninvasive strategies present the lowest risk with the highest potential for patient satisfaction. However, serious implementation barriers exist requiring consistent programmatic screening, strict patient adherence, and poor sensitivity for adenomas. Colonoscopy remains an invasive screening test with the best sensitivity and specificity, but faces large financial costs, manpower requirements, patient access and adherence. Development of advanced molecular techniques identifying altered DNA markers in exfoliated colonocytes signify early or precancerous growth. Stool-based DNA testing provides an entirely noninvasive population-based screening strategy which patients can perform easier than faecal occult blood testing (FOBT). Large-scale prospective randomized control trials currently pending should help characterize accurate test performance, screening intervals, cost-effectiveness, direct comparison to FOBT and analysis of patient adherence. As tumour development pathways and potential target genes are further elucidated, refinements in multi-assay stool-based DNA testing portend enhanced test characteristics to detect and treat this genetically heterogeneous disease.

Detection of K-ras gene mutation in fecal samples from elderly large intestinal cancer patients and its diagnostic significance

AIM: To study the diagnostic significance of K-ras gene mutations in fecal samples from elderly patients with large intestinal cancer.

METHODS: DNA was extracted in the fecal and tissue samples from 23 large intestinal cancer patients, 20 colonic adenomatoid polypus patients and 20 healthy subjects. The K-ras gene mutations at the first and second bases of codon 12 were detected by the allele specific mismatch method.

RESULTS: The K-ras gene mutation was 56.52% (13/23) in the large intestinal cancer patients, which was notably higher than that in the normal subjects whose K-ras gene mutation was 5% (1/20) (Χ² = 12.93, P < 0.001). There was no significant difference in comparison with that of colonic adenomatoid polypus patients whose K-ras gene mutation was 30% (6/12) (Χ² = 3.05, P > 0.05). The K-ras gene mutation at the second base of codon 12 was 92.13% (12/13) in the large intestinal cancer patients. There was no significant difference between the detection rate of K-ras gene mutation in the fecal and tissue samples (Χ² = 9.35, P < 0.01).

CONCLUSION: Our results indicate that detection of the K-ras gene mutations in fecal samples provides a non-invasive diagnostic method for the elderly large intestinal cancer patients. Its significance in the early diagnosis of large intestinal cancer awaits further studies.

DNA enrichment by allele-specific hybridization (DEASH): a novel method for haplotyping and for detecting low-frequency base substitutional variants and recombinant DNA molecules

Detecting rare sequence variants in genomic DNA is central to the analysis of de novo mutation and recombination events and the detection of rare pathological mutations in mixed cell populations. Current PCR techniques suffer from noise that limits detection to variants present at a frequency of at least 10(-4)-10(-5) per cell. We now describe an alternative approach that recovers genomic DNA molecules containing a known single-nucleotide variant by hybridization selection using a biotinylated allele-specific oligonucleotide, followed by hybrid capture on streptavidin-coated paramagnetic beads and subsequent analysis by PCR. This technique of DNA enrichment by allele-specific hybridization (DEASH) is fast, effective for all tested single-nucleotide polymorphisms (SNPs), and can recover large (>10 kb) single-stranded molecules. A single round of DEASH is effective in separating haplotypes from genomic DNA and can not only readily detect and validate DNA molecules containing a single base change at a frequency of 10(-5) per cell, but can also place these changes within the context of an extended haplotype. This technique offers a new approach to the analysis of mutation and recombination, and has the potential to detect very rare de novo base substitutions.

Testing of multiple samples increases the sensitivity of stool decay-accelerating factor test for the detection of colorectal cancer

OBJECTIVES

We previously reported that the measurements of stool decay-accelerating factor (DAF), a membrane-bound, complement regulatory protein, may be valuable for the detection of colorectal cancer. Recently we have refined the immunoassay for stool DAF. In the present study, using the refined assay, we measured stool DAF concentrations in multiple samples from patients with colorectal cancer and in healthy controls to determine whether testing of multiple samples would increase the sensitivity of the stool DAF test.

METHODS

DAF was measured in three spontaneously passed stool samples from each of 100 patients with colorectal cancer and 100 control subjects without apparent colorectal disease.

RESULTS

The stool DAF concentrations in the patients with colorectal cancer (median 11.1 ng/g stool; interquartile range 2.9-32.7 ng/g) were significantly higher than concentrations in the subjects without colorectal diseases (median 1.6 ng/g stool; interquartile range 0.4-3.4 ng/g) (p<0.0001). Testing of two samples from each patient significantly increased the sensitivity (72%) of the stool DAF test without significantly decreasing its specificity (92%). The stool DAF test was positive in more than one half of patients with colorectal cancer at a relatively early TNM stage or with negative fecal occult blood test.

CONCLUSIONS

These findings suggest that stool DAF is a marker of colorectal cancer independent of fecal occult blood and testing of two samples increases the sensitivity of the stool DAF test. Measurement of stool DAF now seems worthy of further consideration as a noninvasive method for the detection of colorectal cancer.

Fecal multiple molecular tests to detect colorectal cancer in stool

BACKGROUND & AIMS

Evaluation of molecular alterations in fecal DNA is a potential, noninvasive, alternative tool for the detection of colorectal cancer. We analyzed a large panel of molecular alterations involved in tumor transformation and progression to define their single diagnostic contribution in terms of sensitivity, cost, and time required to carry out the different tests.

METHODS

DNA was analyzed in stool from 38 healthy individuals and in paired stools and primary lesions from 56 patients with colorectal cancer. p53 exons 5-8, K-ras exons 1-2, four fragments of adenomatous polyposis coli (APC) exon 15, and 5 microsatellite loci were analyzed. Moreover, DNA amplification was evaluated for 4 exons of both p53 and APC.

RESULTS

K-ras (34%) and p53 (34%) mutations were the most frequent alterations in tumors, followed by microsatellite instability (13%) and APC mutations (13%). The most frequent event in stool was DNA amplification (51%), followed by alterations of K-ras (11%), p53 and microsatellite instability (6%), and APC (2%). K-ras and p53 gene mutations increased the capacity of DNA amplification to detect tumor cells by 8%.

CONCLUSIONS

K-ras and p53 gene mutations were the most frequent alterations observed in stool from patients with colorectal cancer, but DNA amplification was even more frequent, being present in more than half of patients. If these preliminary results are confirmed in a prospective study on a larger case series, this approach could be used for noninvasive colon cancer diagnosis in screening programs.

DNA methylation, a biomarker for colorectal cancer: implications for screening and pathological utility

Currently up to one-third of colorectal cancer patients present with locally advanced or metastatic disease that precludes a surgical cure. Performance limitations and low uptake of current screening tools have fueled research to develop minimally invasive approaches that can detect early-stage neoplasms. The observation that altered DNA can be amplified from the stool or circulation has stimulated research on its use as a biomarker of occult neoplasia. De novo methylation of CpG islands 5' to certain tumor suppressor genes has been associated with epigenetic silencing. At certain loci this phenomenon is specific for neoplastic populations, and it is frequently detected at early stages in colorectal tumorigenesis. Accordingly, hypermethylation events have been proposed by researchers as ideal targets for the basis of a screening panel to detect peripheral tumor DNA. This critique reviews research findings on the use of epigenetic biomarkers in screening for occult neoplasia. In addition, the authors consider the pathological utility of epigenetic testing in refining tumor staging and predicting disease recurrence.

Screening for p53 and K-ras mutations in whole-gut lavage in chronic inflammatory bowel disease

OBJECTIVES

Molecular screening for frequently mutated genes may increase the likelihood of identifying cancer risk groups, such as patients with longstanding inflammatory bowel disease. This study investigated the prevalence and time course of p53 and K-ras mutations in colonic lavage fluid of patients with inflammatory bowel disease.

METHODS

Colonic lavage fluid from 190 patients with ulcerative colitis (73), Crohn's disease (58) or controls (49 non-tumour, 10 colorectal cancer) was studied by oligomer-specific hybridization for K-ras mutations and single-strand conformation polymorphism (SSCP) for p53 mutations. Follow-up investigations were carried out after 1-3 years.

RESULTS

Mutations were most frequent in carcinomas (5/10, 50%) and rare in non-tumour controls (1/49, 2.0%). They were found in Crohn's colitis in 15.4%, in extensive ulcerative colitis in 18.6%, in left-sided ulcerative colitis in 13.3%, and in distal ulcerative colitis in 6.7% (P > 0.05). There was a positive association with disease duration (> or =11 years, P < 0.05). Follow-up investigations detected the same mutation in four patients and revealed new mutations in three patients.

CONCLUSIONS

In our large series of patients with inflammatory bowel disease, K-ras and p53 mutations could be detected with reasonable frequency and confirmed at follow-up in at least some patients. Our data encourage the use of molecular screening for the detection of malignant precursor lesions in at-risk patients.

K-ras mutations in sporadic colorectal tumors in Israel: unusual high frequency of codon 13 mutations and evidence for nonhomogeneous representation of mutation subtypes

Colorectal cancer is one of the most common malignancies in the western world, including Israel. An important step in progression includes induction of activating mutations in the protooncogene K-ras. This event is very frequent and is detected in about 40% of colorectal carcinomas. Previous studies of a variety of genetic disorders revealed unique gene mutation prevalence in Jewish populations, attributed both to differences in genetic background and to variability in environmental exposure. To determine the incidence and molecular subtypes of K-ras mutations in colorectal cancer in Israel, compared with other countries, DNA was isolated from a random collection of 105 colorectal carcinoma samples, and K-ras mutations were detected by an improved designed RFLP and direct sequencing. K-ras sporadic mutations in colorectal cancer in Israel are relatively frequent, with a higher fraction in codon 13 than reported thus far. Comparison with other countries shows a vast heterogeneity in terms of the relative abundance of the affected K-ras codon and in type and representation of specific mutations. The heterogeneous distribution found may be due to a variable genetic background and different environmental factors involved in the initiation and propagation of sporadic colorectal cancer.

Microsatellite analysis of fecal DNA for colorectal cancer detection

BACKGROUND AND OBJECTIVES

The advent of noninvasive methods of testing for colorectal cancer that have a high level of specificity and sensitivity is eagerly awaited.

METHODS

Thirty patients with sporadic colorectal cancer and 11 patients with hereditary nonpolyposis colon cancer (HNPCC) enrolled in this study. We analyzed the loss of heterozygosity (LOH) in matched genomic DNA extracted from blood and surgical specimens (tumor and tumor-free colonic mucosa), and the corresponding oral rinse and stool specimens using seven microsatellite loci (APC, p53, DCC, hMLH1, D9S162, D9S171, and IFNA). To reduce the normal colonocyte DNA contamination of the stool samples, we compared three different methods for fecal genomic DNA extraction. As normal controls, we analyzed the LOH using the oral rinse and stool samples from 15 individuals without cancer.

RESULTS

The LOH determined from the oral rinse and the stool samples matched those determined from the blood and the neoplastic tissue. All patients with HNPCC had microsatellite alterations at hMLH-1 in tumor DNA and corresponding fecal DNA. There were significant differences in the frequency of p53-LOH and D9S171-LOH between the group with sporadic disease and those with HNSCC (P = 0.0031 and 0.0294, respectively). Two cases with D9S162-LOH were detected in individuals without cancer. For the patients with sporadic disease, using p53 and adenomatous polyposis coli (APC), the sensitivity of the fecal DNA analysis was 96.7% (95% CI, 83-100) with a specificity of 100%.

CONCLUSION

We demonstrate that LOH analysis using oral rinse and stool samples may be a suitable screening tool for colorectal cancer.

A simple method of detecting K-ras point mutations in stool samples for colorectal cancer screening using one-step polymerase chain reaction/restriction fragment length polymorphism analysis

BACKGROUND

We examined a technique for detecting point mutations of K-ras codon 12 in stool samples using one-step polymerase chain reaction/restriction fragment length polymorphism (PCR/RFLP) analysis, in order to determine whether it could be used to screen for colorectal cancer.

METHODS

DNA was extracted from 200-mg stool specimens of 5 healthy controls and 31 colorectal cancer patients. A 107-base-pair fragment of exon 1 of K-ras was amplified by PCR using mismatched primers. PCR products were digested with Bst NI and analyzed by gel electrophoresis followed by silver staining. Specificity of one-step PCR/RFLP was examined by using synthetic oligonucleotides. The detection limit of K-ras codon 12 mutations was determined by using SW480 and HT29 cells.

RESULTS

The K-ras gene was successfully amplified from all healthy controls and colorectal cancer patients studied. Mutations of K-ras codon 12 were not detected in any of the healthy controls, but were identified in 13 (41.9%) of the 31 patients with colorectal cancer. Mutations were detectable in all six synthetic mutant DNAs, while none were detected among the wild type. The detection limit of this method was > or = 0.1%.

CONCLUSIONS

PCR/RFLP analysis could be used in mass screening for colorectal cancer, because it is highly specific, has a low detection limit, and is simpler than conventional methods for detecting genetic abnormalities.

Isolation of exfoliated colonocytes from human stool as a new technique for colonic cytology

Cell exfoliation in the gut is an important cell renewal mechanism. To approach its investigation we applied a novel immunomagnetic technique for isolation of exfoliated cells from human stool. Exfoliated colonocytes were isolated from 168 stool samples. The cells were assessed microscopically using conventional stains and immunohistochemistry. The technique allowed us to obtain well-preserved colonocytes displaying characteristic features of well-differentiated colonic epithelium and positive immunostaining for cytokeratin 5/8. No mucin-producing cells were found. Exfoliated cells did not produce inducible nitric oxide synthase, albeit cultured colon carcinoma cells HT-29 analysed in parallel showed strong immunostaining. Analysis of exfoliated cell numbers in consecutive stool samples from the same subjects revealed considerable interindividual variation. Overall exfoliated colonocyte numbers were relatively low, isolation being unaffected by addition during the procedure of excessive amounts of HT-29 cells. Apoptosis was extremely rare among exfoliated colonocytes. Well-preserved exfoliated colonocytes can be consistently isolated from human faeces using a simple procedure. Our findings suggest that the actual process of cell exfoliation in the human colon may be much less intense than is generally accepted. Exfoliated cell isolation from human stool constitutes a convenient non-invasive approach that can be used for diagnostic and research purposes.

Detection of APC mutations in fecal DNA from patients with colorectal tumors

BACKGROUND

Noninvasive methods for detecting colorectal tumors have the potential to reduce morbidity and mortality from this disease. The mutations in the adenomatous polyposis coli (APC) gene that initiate colorectal tumors theoretically provide an optimal marker for detecting colorectal tumors. The purpose of our study was to determine the feasibility of detecting APC mutations in fecal DNA with the use of newly developed methods.

METHODS

We purified DNA from routinely collected stool samples and screened for APC mutations with the use of a novel approach called digital protein truncation. Many different mutations could potentially be identified in a sensitive and specific manner with this technique.

RESULTS

Stool samples from 28 patients with nonmetastatic colorectal cancers, 18 patients with adenomas that were at least 1 cm in diameter, and 28 control patients without neoplastic disease were studied. APC mutations were identified in 26 of the 46 patients with neoplasia (57 percent; 95 percent confidence interval, 41 to 71 percent) and in none of the 28 control patients (0 percent; 95 percent confidence interval, 0 to 12 percent; P<0.001). In the patients with positive tests, mutant APC genes made up 0.4 to 14.1 percent of all APC genes in the stool.

CONCLUSIONS

APC mutations can be detected in fecal DNA from patients with relatively early colorectal tumors. This feasibility study suggests a new approach for the early detection of colorectal neoplasms.

Stool screening for colorectal cancer: evolution from occult blood to molecular markers

BACKGROUND

Colorectal cancer is the second leading cause of malignant death, and better preventive strategies are needed. Participation rates for colorectal cancer screening remain low due, in part, to perceived discomfort, potential harm, and high costs with available tools.

METHODS

Stool testing, unlike other conventional screening approaches, is noninvasive and requires no cathartic preparation. However, widely used fecal blood tests yield frequent false-negative and false-positive results that lower screening effectiveness and raise program costs. There is a compelling biological rationale to target DNA alterations exfoliated from neoplasms into stool, and multiple DNA markers would need to be assayed because of the genetic heterogeneity of colorectal neoplasia. Early clinical studies with this multi-target DNA-based stool assay approach suggest high sensitivity for both colorectal cancer and premalignant adenomatous polyps while maintaining high specificity.

CONCLUSIONS

This apparently accurate and user-friendly new approach holds promise to improve the effectiveness, efficiency, and appeal of colorectal cancer screening. Large-scale clinical studies are clearly warranted to corroborate the early results.

Gene mutation as a target for early detection in cancer diagnosis

The increasing number of genetic aberrations implicated in the development of human cancer has prompted a search to detect them at the earliest possible stage of their formation. Of the many such genetic changes identified thus far, relatively few meet the standard for markers in early diagnosis and prognosis, namely that the genetic modifications occur during the early onset phase of cancer development. Parallel to the increasing number of such genes is the growing availability of technologies using more powerful and cost-efficient methods that enable mass screening for genetic alterations. The purpose of this review is to summarize the currently available genes that can serve as markers for early detection of cancers and methods that allow their detection.

Detecting colorectal cancer in stool with the use of multiple genetic targets

BACKGROUND

Colorectal cancer cells are shed into the stool, providing a potential means for the early detection of the disease using noninvasive approaches. Our goal was to develop reliable, specific molecular genetic tests for the detection of colorectal cancer in stool samples.

METHODS

Stool DNA was isolated from paired stools and primary tumor samples from 51 colorectal cancer patients. Three genetic targets-TP53, BAT26, and K-RAS-were used to detect tumor-associated mutations in the stool prior to or without regard to the molecular analyses of the paired tumors. TP53 gene mutations were detected with a mismatch-ligation assay that detects nine common p53 gene mutations. Deletions within the BAT26 locus were detected by a modified solid-phase minisequencing method. Mutations in codons 12 and 13 of K-RAS were detected with a digital polymerase chain reaction-based method.

RESULTS

TP53 gene mutations were detected in the tumor DNA of 30 patients, all of whom had the identical TP53 mutation in their stools. Tumors from three patients contained a noninherited deletion at the BAT26 locus, and the same alterations were identified in these patients' stool specimens. Nineteen of 50 tumors tested had a K-RAS mutation; identical mutations were detected in the paired stool DNA samples from eight patients. In no case was a mutation found in stool that was not also present in the primary tumor. Thus, the three genetic markers together detected 36 (71%) of 51 patients (95% confidence interval [CI] = 56% to 83%) with colorectal cancer and 36 (92%) of 39 patients (95% CI = 79% to 98%) whose tumors had an alteration.

CONCLUSION

We were able to detect the majority of colorectal cancers by analyzing stool DNA for just three genetic markers. Additional work is needed to determine the specificity of these genetic tests for detecting colorectal neoplasia in asymptomatic patients and to more precisely estimate the prevalence of the mutations and sensitivity of the assay.

Detection of the mutated K-Ras biomarker in colorectal carcinoma

This study describes an advantageous, effective protocol for detecting K-Ras mutations in human stool as a prototype screen for colorectal carcinoma (CRC), the third most common malignancy in the United States. A reliable screening test that detects early lesions would contribute to a decrease in mortality. Currently, the only noninvasive screen for CRC is the hemeoccult, test which has a high false-positive rate. Previously, several investigators have identified genetic biomarkers for CRC in stool DNA. The K-Ras oncogene, mutated in 46-50% of CRC tumors, serves as one molecular marker by which stool samples may be evaluated for early detection of adenocarcinomas. DNA was isolated from stool samples by a new method we specifically designed for extracting high-quality DNA using tetradecyltrimethylammonium oxalate [Catrimox-14, Iowa Biotechnology Corp., (currently Qiagen)]. This protocol produces an optimal yield of high-purity DNA, suitable for genotyping. Detection of the human gene in stool samples was enhanced by hybrid selection of the K-Ras sequences, polymerase chain reaction, and single-strand conformation polymorphism. Tumor tissue and preoperative stool samples for eight patients were K-Ras genotyped and compared; stool samples from two asymptomatic, healthy patients were also evaluated in a double-blind format. In seven of eight samples (87%), the genotypes of the stool and colon tissue DNA were the same. Both healthy patients showed wild-type K-Ras. This protocol shows promise for the development of an efficient and accurate screen for CRC.

Enrichment of mutant KRAS alleles in pancreatic juice by subtractive iterative polymerase chain reaction

SUMMARY

The detection of mutant tumor genes holds great promise for an early diagnosis of primary tumors and residual malignant disease. When few tumor cells are present with an excess of nonmalignant cells of the same lineage, the excess of wild-type alleles over mutant tumor alleles presents an analytical problem. The subtractive iterative PCR (siPCR) assay presents a new approach to solving this problem. To achieve an enrichment of mutant alleles, wild-type alleles are removed by differential hybridization to complementary oligonucleotides spanning the region of the gene in which point mutations are expected. The nonbound fraction is reamplified by PCR. By iterating this process, mutant alleles can be detected in the presence of an excess of wild-type alleles with high sensitivity. To prove the feasibility of siPCR, pancreatic juice samples were analyzed for KRAS mutations. Pancreatic juice obtained from patients with pancreatic carcinoma or chronic pancreatitis during endoscopic retrograde cholangiopancreatography was analyzed for point mutations in codons 12 and 13 of the KRAS gene. In each of six samples from tumor patients, mutations in codon 12 were detected. One of nine samples from patients with chronic pancreatitis scored positive.

Alkaline-mediated differential interaction (AMDI): a simple automatable single-nucleotide polymorphism assay

The key requirements for high-throughput single-nucleotide polymorphism (SNP) typing of DNA samples in large-scale disease case-control studies are automatability, simplicity, and robustness, coupled with minimal cost. In this paper we describe a fluorescence technique for the detection of SNPs that have been amplified by using the amplification refractory mutation system (ARMS)-PCR procedure. Its performance was evaluated using 32 sequence-specific primer mixes to assign the HLA-DRB alleles to 80 lymphoblastoid cell line DNAs chosen from our database for their diversity. All had been typed previously by alternative methods, either direct sequencing or gel electrophoresis. We believe the detection system that we call AMDI (alkaline-mediated differential interaction) satisfies the above criteria and is suitable for general high-throughput SNP typing.

Colorectal cancer screening by detection of altered human DNA in stool: feasibility of a multitarget assay panel

BACKGROUND & AIMS

Assay of altered DNA exfoliated into stool represents an intriguing approach to screen for colorectal neoplasia, but multiple markers must be targeted because of genetic heterogeneity. We explored the feasibility of a stool assay panel of selected DNA alterations in discriminating subjects with colorectal neoplasia from those without.

METHODS

Freezer-archived stools were analyzed in blinded fashion from 22 patients with colorectal cancer, 11 with adenomas > or =1 cm, and 28 with endoscopically normal colons. After isolation of human DNA from stool by sequence-specific hybrid capture, assay targets included point mutations at any of 15 sites on K-ras, p53, and APC genes; Bat-26, a microsatellite instability marker; and highly amplifiable DNA.

RESULTS

Analyzable human DNA was recovered from all stools. Sensitivity was 91% (95% confidence interval, 71%-99%) for cancer and 82% (48%-98%) for adenomas > or =1 cm with a specificity of 93% (76%-99%). Excluding K-ras from the panel, sensitivities for cancer were unchanged but decreased slightly for adenomas to 73% (39%-94%), while specificity increased to 100% (88%-100%).

CONCLUSIONS

Assay of altered DNA holds promise as a stool screening approach for colorectal neoplasia. Larger clinical investigations are indicated.

Utilization of K-ras mutations identified in stool DNA for the early detection of colorectal cancer

Colorectal cancer is one of the most common malignancies in the western world. About 60,000 Americans die of colorectal cancer each year. The annual incidence rate in Israel is 40 per 100,000 persons, namely a total of 2,000 new cases each year. An important step in the progression of colorectal cancer includes induction of activating mutations in the proto-oncogene K-ras. The mutations in K-ras appear early during tumorigenesis, at the intermediate adenoma stage, and thus can be used as a biomarker for early detection in about 40% of colonic tumors. A large yet unknown number of mutated cells are shed from the developing tumor during its progression. Indeed, K-ras mutations were detected in DNA isolated from stool obtained from symptomatic and asymptomatic patients with colorectal cancer, suggesting a novel approach for a noninvasive screening procedure. However, severe difficulties in obtaining reproducible yields of amplifiable DNA from stool, and usage of nonquantitative, time-consuming procedures, hampered further progress in the utilization of K-ras mutations for the early detection of colorectal cancer. Apparently a novel protocol is required that provides reproducible output of amplifiable DNA from small amounts of stool, detects if K-ras mutated DNA is present, and determines the quantity of K-ras mutated cells in the stool sample. In addition, this protocol should be simple, robotics compatible, and thus suitable for cost-effective, large-scale mutation screening. Molecular assays for detecting K-ras mutations and additional biomarkers in stool DNA promise to be highly sensitive, specific, and cost-effective. As such they should be very effective when used in chemoprevention studies and screening protocols for colorectal cancer.

Molecular screening for colon cancer detection

Screening for colorectal cancer is a widely debated issue. Faecal occult blood testing is, at present, the only single test available which is applicable to large populations. However, progress in the definition of genetic alterations in the aetiopathogenesis both of sporadic and hereditary colorectal cancer have made it possible to set up molecular methods for identifying subjects with colorectal cancer or who are at risk of developing it. The target genes involved and the source of genomic material to be studied are different for sporadic and hereditary conditions and determine the type of test to use.

K-ras and p53 mutations in DNA extracted from colonic epithelial cells exfoliated in faeces of patients with colorectal cancer

BACKGROUND

Exfoliated colonic epithelial cells in faeces provide a source of human DNA which may be analysed for the presence of tumour-induced modification.

AIM

In the present study we investigated K-ras and p53 mutations in faeces of patients with colorectal carcinoma, to verify whether analysis of these mutations might identify a high percentage of patients with colorectal cancer.

PATIENTS AND METHODS

Faeces, tumour and normal mucosa samples were taken from 26 patients. Polymerase chain reaction amplification and restriction enzyme analysis were performed to detect K-ras mutations; p53 gene mutations were identified by using polymerase chain reaction amplification and single strand conformation polymorphism.

RESULTS

We were able to amplify the K-ras gene and exons 5-9 of the p53 gene in 100% of the faecal samples studied. K-ras and p53 gene mutations were detected in faeces in 26.9% and 50% of the cases, respectively. The two mutations were present together in 5 out of 26 patients. There was full agreement between the K-ras and p53 pattern observed in faecal DNA and that in tumour tissue DNA.

CONCLUSIONS

Application of K-ras and p53 mutation gene analysis in the faeces may have clinical applications in the future. Since this genetic analysis is able to detect only 57.7% of patients with colorectal cancer, the study of other genes involved in colorectal carcinogenesis is necessary.

A highly sensitive method for K-ras mutation detection is useful in diagnosis of gastrointestinal cancer

Detection of molecular features such as K-ras mutations has been used to evaluate potential tumour markers in a wide variety of clinical samples. Here we have applied a recently developed highly sensitive method for detection of K-ras codon 12 mutations to colorectal and pancreatic cancer diagnosis. We analysed 67 faecal samples from patients undergoing diagnostic colonoscopy under suspicion of colorectal cancer. PCR products were obtained in 62 of 67 (93%) faecal samples. Mutations were detected in exfoliated cells in 6 of 22 (27%) of the adenomas and in 6 of 11 (55%) of adenocarcinomas. No false positives were observed. Agreement between faecal samples and corresponding tissues was 100% for adenocarcinomas and 65% for adenomas. Mutations were also analysed in 61 pancreatic fine-needle aspirates. Mutations were detected in 36 of 45 (80%) of the pancreatic aspirates diagnosed as pancreatic cancer without false positives. Our findings suggest that, when colorectal cancer is suspected, detection of K-ras codon 12 mutations in faecal samples using this new method is specific for colorectal tumours. Additionally, this technique is a good alternative for evaluation of pancreatic masses.

Digital PCR

The identification of predefined mutations expected to be present in a minor fraction of a cell population is important for a variety of basic research and clinical applications. Here, we describe an approach for transforming the exponential, analog nature of the PCR into a linear, digital signal suitable for this purpose. Single molecules are isolated by dilution and individually amplified by PCR; each product is then analyzed separately for the presence of mutations by using fluorescent probes. The feasibility of the approach is demonstrated through the detection of a mutant ras oncogene in the stool of patients with colorectal cancer. The process provides a reliable and quantitative measure of the proportion of variant sequences within a DNA sample.

Molecular screening of patients with long standing extensive ulcerative colitis: detection of p53 and Ki-ras mutations by single strand conformation polymorphism analysis and differential hybridisation in colonic lavage fluid

BACKGROUND

In patients with long standing ulcerative colitis at risk of developing malignancy, mutations of the p53 and Ki-ras gene were investigated in lavage solution obtained at surveillance colonoscopy.

METHODS

DNA was isolated from 31 consecutive patients with total or subtotal ulcerative colitis and a disease duration of between seven and 26 years. Twenty seven control patients showed no macroscopic or microscopic inflammation on colonoscopy. Exons 5-8 of the p53 gene and exon 1 of the Ki-ras gene were amplified by polymerase chain reaction. Mutations of the p53 gene were detected by single strand conformation polymorphism analysis. Point mutations of the Ki-ras gene were hybridised on dot blots with oligonucleotides marked with digoxigenin.

RESULTS

In all cases of ulcerative colitis and in all of the 27 control patients, wild type p53 and wild type Ki-ras could be detected. In four patients with ulcerative colitis, a mutation in exon 5 to 7 of the p53 gene was found, and two patients had a mutation of the Ki-ras gene (Gly to Asp-12, Gly to Val-12). None of these patients had dysplasia in serial biopsy specimens, and all but one had had the disease for more than 10 years. One control patient had a mutation.

CONCLUSIONS

Mutations were more frequent in patients with long standing ulcerative colitis (19%) than in control patients (3%, p = 0.07). The technique may be useful for screening for early malignancy in ulcerative colitis.