Identification of ras oncogene mutations in the stool of patients with curable colorectal tumors

Colon cancer: prevalence, screening, gene expression and mutation, and risk factors and assessment

Colon cancer detection at an early stage and identifying susceptible individuals can result in reduced mortality from this prevalent cancer. Genetic events leading to the development of this cancer involve a multistage progression of adenoma polyps to invasive metastatic carcinomas. Currently, there is no satisfactory screening method that is highly specific, sensitive, or reliable. Dietary patterns associated with the greatest increase in colon cancer risk are the ones that typify a diet rich in fat and calories, and low in vegetable, fruits, and fibers. Genetic susceptibility to environmental carcinogenesis must be factored into the risk assessment for this cancer. Many genes have been shown to be associated with increased expression and mutations in colorectal cancer patients. These genes have been reviewed; it is hoped that by carefully selecting a number of them, a molecular approach that is suitable for arriving at a tumorigenic expression index is developed, which will reliably detect this cancer at an early stage (i.e., before it metastasizes), especially in exfoliated samples (e.g., stool and blood), so that appropriate intervention strategies can be implemented. Illustrated herein is the utility of employing real-time reverse transcriptase polymerase chain reaction (RT-PCR) to quantitatively measure gene expression, and develop an index that is specific for this cancer, which if perfected may result in a reliable and sensitive screening technique for colorectal cancer detection.

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.

Development of gamma (gamma)-tocopherol as a colorectal cancer chemopreventive agent

Nutritional factors play an important role in the prevention and promotion of colorectal cancer. Vitamin E is a generic term that describes a group of lipid-soluble chain-breaking antioxidants that includes tocopherols and tocotrienols. Vitamin E occurs in nature as eight structurally related forms that include four tocopherols and four tocotrienols. Vitamin E is a potent membrane-soluble antioxidant. Antioxidants like vitamin E (tocopherols) may prevent colon cancer through several different cellular and molecular mechanisms. Vitamin E in the American diet is primarily available in plant-oil rich foods such as vegetable oils, seeds and nuts and these foods vary widely in their content of alpha-tocopherol and gamma-tocopherol. Vitamin E may help prevent colon cancer by decreasing the formation of mutagens arising from the oxidation of fecal lipids, by decreasing oxidative stress in the epithelial cells of the colon and by molecular mechanisms that influence cell death, cell cycle and transcriptional events. Most epidemiological, experimental and clinical studies have evaluated the alpha-isoform and not the gamma-isoform of vitamin E. Recent epidemiological, experimental and mechanistic evidence suggests that gamma-tocopherol may be a more potent cancer chemopreventive agent than alpha-tocopherol. The differences in chemical reactivity, metabolism and biological activity may contribute to these differences in the effects of gamma-tocopherol when compared with alpha-tocopherol. The rationale supporting the development of gamma-tocopherol as a colorectal cancer preventive agent is reviewed here.

DNA integrity as a potential marker for stool-based detection of colorectal cancer

BACKGROUND

Molecular genetic analysis of DNA in patient stools has been proposed for screening of colorectal cancer (CRC). Because nonapoptotic cells shed from tumors may contain DNA that is less degraded than DNA fragments from healthy colonic mucosa, our aim was to show that DNA fragments isolated from stools of patients with CRC had higher integrity than DNA isolated from stools of patients with healthy colonic mucosa.

METHODS

We purified DNA from the stools of a colonoscopy-negative control group and patients with CRC and examined the relationship between long DNA fragments and clinical status by determining stool DNA integrity, using oligonucleotide-based hybrid captures with specific target sequences in increasingly long PCR reactions (200 bp, 400 bp, 800 bp, 1.3 kb, 1.8 kb, 24 kb). DNA fragments obtained from CRC patients were compared with fragments obtained from colonoscopy-negative individuals for length and/or integrity.

RESULTS

DNA fragments isolated from CRC patients were of higher molecular weight (>18 bands detected of a total of 24 possible bands) than fragments isolated from fecal DNA of the colonoscopy-negative control group.

CONCLUSIONS

The presence of long DNA fragments in stool is associated with CRC and may be related to disease-associated differences in the regulation of proliferation and apoptosis. An assay of fecal DNA integrity may be a useful biomarker for the detection of CRC.

Clinical utility of biochemical markers in colorectal cancer: European Group on Tumour Markers (EGTM) guidelines

In recent years, numerous serum and cell/tissue-based markers have been described for colorectal cancer (CRC). The aim of this article was to provide guidelines for the routine clinical use of some of these markers. Lack of sensitivity and specificity preclude the use of any available serum markers such as carcinoembryonic antigen (CEA), CA 19-9, CA 242, CA 72-4, tissue polypeptide antigen (TPA) or tissue polypeptide-specific antigen (TPS) for the early detection of CRC. However, preoperative measurement of CEA is desirable as this may give independent prognostic information, help with surgical management and provide a baseline level for subsequent determinations. For patients with stage 2 (Dukes' B) and 3 (Dukes' C) disease who may be candidates for liver resection, CEA levels should be measured every 2-3 months for at least 3 years after diagnosis. For monitoring treatment of advanced disease, CEA should also be tested every 2-3 months. Insufficient evidence is presently available to recommend the routine use of other serum markers for monitoring purposes. Similarly, the new cell and tissue-based markers (e.g, ras, P53) cannot yet be recommended for routine clinical use.

Colorectal cancer screening: scientific review

CONTEXT

Screening for colorectal cancer clearly reduces colorectal cancer mortality, yet many eligible adults remain unscreened. Several screening tests are available, and various professional organizations have differing recommendations on which screening test to use. Clinicians are challenged to ensure that eligible patients undergo colorectal cancer screening and to guide patients in choosing what tests to receive.

OBJECTIVE

To critically assess the evidence for use of the available colorectal cancer screening tests, including fecal occult blood tests, sigmoidoscopy, colonoscopy, double-contrast barium enema, and newer tests, such as virtual colonoscopy and stool-based molecular screening.

DATA SOURCES

All relevant English-language articles were identified using PubMed (January 1966-August 2002), published meta-analyses, reference lists of key articles, and expert consultation.

DATA EXTRACTION

Studies that evaluated colorectal cancer screening in healthy individuals and assessed clinical outcomes were included. Evidence from randomized controlled trials was considered to be of highest quality, followed by observational evidence. Diagnostic accuracy studies were evaluated when randomized controlled trials and observational studies were not available or did not provide adequate evidence. Studies were excluded if they did not evaluate colorectal screening tests and if they did not evaluate average-risk individuals.

DATA SYNTHESIS

Randomized controlled trials have shown that fecal occult blood testing can reduce colorectal cancer incidence and mortality. Case-control studies have shown that sigmoidoscopy is associated with a reduction in mortality, and observational studies suggest colonoscopy is effective as well. Combining fecal occult blood testing and sigmoidoscopy may decrease mortality and can increase diagnostic yield.

CONCLUSION

The recommendation that all men and women aged 50 years or older undergo screening for colorectal cancer is supported by a large body of direct and indirect evidence. At present, the available evidence does not currently support choosing one test over another.

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.

Genetic chaos and antichaos in human cancers

Cancer is considered the genetic disease with the most complex pathogenetic mechanism. Contrary to normal human tissues, which function in a highly ordered and uniform manner, tumor tissues were considered to develop chaos. Here we propose that analysis of human neoplasia according to the concepts of chaos and antichaos allowed to distinguish two main types of cancers: the hematopoietic cancers, characterized by the orderly antichaos and solid cancers governed by a disordered complex of genetic and molecular events characteristic of a chaotic pattern. Genetic chaos and antichaos have generated rules that can be applied to the diagnosis and therapy of human tumors.

Quantification of human intestinal gene expression profiles using exfoliated colonocytes: a pilot study

Early detection of colon cancer can result in a high cure rate; therefore, an accurate screening method is imperative. Adoption of non-invasive testing designed to reduce anxiety over colorectal cancer screening and improve early detection is highly desirable. Therefore, we have developed a novel non-invasive methodology utilizing exfoliated colonocytes in order to quantify colonic messenger RNAs (mRNAs). Previously we have demonstrated in the rat that intact eukaryotic mRNA can be isolated due to the presence of exfoliated colonocytes in the faecal stream. To assess use of this methodology in humans, this pilot study evaluated exfoliated colonocyte mRNA expression of 11 putative biomarkers using real-time reverse transcription-polymerase chain reaction (RT-PCR) in seven normal subjects, four subjects with inflammation, and 10 tumour-bearing subjects presenting for colonoscopy. Expression of the biomarkers was evaluated following normalization to TATA box binding protein mRNA levels. Tumour-bearing subjects diagnosed with adenoma had elevated levels of cyclin Dl (p = 0.041). In addition, subjects displaying inflammation of the colon exhibited higher mRNA levels of cyclooxygenase-2 (p = 0.007). These data suggest that mRNA isolated from exfoliated colonocytes could be used to detect early stages of colon cancer, and possibly chronic inflammation. To broaden the utility of non-invasive marker analysis, additional studies are needed to generate a multi-target assay panel of diagnostic markers. This will allow for the development of robust classifiers that can determine critical gene sets for the diagnosis and prediction of colon cancer in animal models and humans.

Detection of tumor DNA in serum of colorectal cancer patients

We previously found p16 promoter methylation in DNA in the sera of 13 colorectal cancer patients out of 44 (30%) whose tumor DNA exhibited the methylation, using methylation-specific PCR (MSP). To examine whether the cancer detection rate could be improved by using a different tumor marker, we examined the K-ras status in 90 colorectal cancer patients using a mismatch ligation assay. Among the 31 patients showing K-ras gene mutations in their tumors, the same mutations were observed in serum DNA of 11 patients (35%). Among the 90 patients, 63 showed tumors positive for K-ras mutation or p16 promoter methylation, or both, and 22 had serum DNA positive for one or both. K-ras mutation was found even in serum DNA of patients with Dukes A cancer, suggesting that colorectal cancer might be detected even in patients without symptoms by using this ligation assay.

Innovative molecular and imaging approaches for the detection of lung cancer and its precursor lesions

Current approaches for the therapy of lung cancer, the majority of which being advanced cancers, have failed to impact on long term survival. The key to improvement lies in the combination of early diagnosis and the introduction of novel targeted therapies. In this article we review some of the innovative approaches, both imaging and molecular, that are currently under investigation for early detection. Because lung cancers may arise in the central or peripheral compartments of the lung, newer approaches must target tumours arising in both of these compartments. Specimens available for analysis include sputa and blood. Detection of genetic changes in peripheral blood is a promising avenue being explored by several groups. Molecular techniques discussed include gene mutations, detection of nuclear riboprotein, methylation related silencing of genes and malignancy associated changes. Newer imaging technologies include autofluorescence bronchoscopy, virtual bronchoscopy, optical coherent tomography and confocal microscopy. Although the impact of these new technologies on survival has not been determined, they offer a wide range of exciting new approaches. In time they may completely revamp the present highly conservative and unsuccessful approaches to early diagnosis.

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.

Development of a fecal occult blood test using a monoclonal antibody to haptoglobin

Monoclonal antibodies (mAbs) were produced to human haptoglobin by immunising with fecal extracts from patients with colon cancer. An enzyme-linked immunosorbent assay was developed with one of the mAbs (FE14.1), and its ability to diagnose colorectal carcinoma evaluated. Patients with colorectal cancer were positive (43/46 = 93.5%) compared to normal individuals (4/211 = 1.9%). The assay has a specificity 93.5% and sensitivity 98.1% and has several advantages over current fecal occult blood tests. The test is potentially useful for bowel cancer diagnosis and to quantitate the level of haptoglobin in other body fluids such as urine and in effusions.

Detection of free-circulating tumor-associated DNA in plasma of colorectal cancer patients and its association with prognosis

Tumor cells are characterized by specific genetic alterations. When such genetic alterations are identified in body fluid including plasma, regardless of the presence of detectable tumor cells, it shows the existence of free-circulating tumor-associated DNA. The objective of our study was to assess the prognostic value of free-circulating tumor-associated DNA in colorectal cancer patients' plasma. The first step of our work was to find common genetic alterations in tumors that would subsequently be used for plasma DNA screening. We focused on KRAS2 mutations in codons 12 and 13 by the mutant allele-specific amplification (MASA) method and p16 hypermethylation by the methylation-specific polymerase chain reaction (MSP) method. Patients with a tumor presenting either alteration were selected for plasma screening; 58 tumors were analyzed for KRAS2 mutations and tested for p16 gene promoter methylation. Survival and recurrence rates were assessed in patients with and without free-circulating tumor-associated DNA alterations in plasma. Of the 58 tumors analyzed, 39 (67%) demonstrated either one or both of the studied genetic alterations. Twenty-two (38%) were mutated at KRAS2, and an identical alteration was detected in 10 (45%) of the 22 corresponding plasma samples. Thirty-one (53%) had p16 gene promoter hypermethylation that could also be detected in the plasma in 21 cases (68%). Among the 39 patients who had one or the other alteration in tumor DNA, 37 had at least one reliable plasma test. In 26 (70%) of the 37 patients, free-circulating tumor-associated DNA was detected in plasma. The 2-year overall survival rate was 48% in the group where free-circulating tumor-associated DNA was detected in plasma and 100% in the one where free-circulating tumor-associated DNA was not detected in plasma (p < 0.03). Among these 37 patients, 25 patients had a stage I, II or III disease. In this subgroup of patients, the 2-year recurrence-free survival rate for the 17 patients with free-circulating tumor-associated DNA detected in plasma was 66%, compared to 100% for the 8 patients without free-circulating tumor-associated DNA detected in plasma (p = 0.044). The presence of free-circulating tumor-associated DNA in plasma seems to be a relevant prognostic marker for patients with colorectal cancer and may be used to identify patients with a high risk of recurrence.

The promise of biomarkers in cancer screening and detection

Despite the recent decline in the incidence of cancer, long-term mortality rates remain unchanged. One of the most important factors in the survival of cancer is detection at an early stage. Clinical assays that detect the early events of cancer offer an opportunity to intervene and prevent cancer progression. Biomarkers are important molecular signatures of the phenotype of a cell that aid in early cancer detection and risk assessment. Although new information and technologies are clearly important for new biomarker discovery, we face major hurdles in translating new findings into clinical application. Here, we discuss examples of recent advances and limitations in cancer biomarker identification and validation, and the implications for cancer prevention.

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.

Epidemiology and screening of colorectal cancer

Knowledge of the descriptive epidemiology of colorectal cancer is essential to a better understanding of the aetiology of the disease and the development of screening strategies. Considerable research efforts have been launched over the last 15 years to evaluate the ability of screening tests to decrease the incidence and mortality of colorectal cancer. This chapter provides a worldwide update of the incidence of colorectal cancer and reviews the evidence for screening for colorectal cancer based on published studies.

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.

Emerging molecular markers of cancer

Alterations in gene sequences, expression levels and protein structure or function have been associated with every type of cancer. These 'molecular markers' can be useful in detecting cancer, determining prognosis and monitoring disease progression or therapeutic response. But what is the best way to identify molecular markers and can they be easily incorporated into the clinical setting?

Molecular detection of gene mutations and methylation abnormalities: applications in solid tumor diagnosis

As our knowledge of the genetic and epigenetic abnormalities initiating and contributing to tumorigenesis grows, so too does the scope for earlier detection of cancer in patients. This bears an immense potential impact on the clinical management of patients with or at risk of solid tumors, since arguably the greatest problem facing clinicians is late presentation. PCR-based tests have been developed to detect mutant or hypermethylated alleles in exfoliative material and plasma/serum, enabling risk-assessment and early detection programs. Although there are certain limitations, a number of studies have already demonstrated the feasibility and reliability of molecular screening in solid tumors, including colorectal and lung cancers and such molecular approaches may soon be used routinely to detect precursor lesions and early-stage cancer.

Diagnostic Biochip Array for Fast and Sensitive Detection of K-ras Mutations in Stool

Background: Tumor cells that shed into stool are attractive targets for molecular screening and early detection of colon or pancreatic malignancies. We developed a diagnostic test to screen for 10 of the most common mutations of codons 12 and 13 of the K-ras gene by hybridization to a new biochip array.

Methods: DNA was isolated from 26 stool samples by column-based extraction from 9 cell lines. Peptide nucleic acid (PNA)-mediated PCR clamping was used for mutant-specific amplification. We used a biochip, consisting of a small plastic support with covalently immobilized 13mer oligonucleotides. The read out of the biochip was done by confocal time-resolved laser scanning. Hybridization, scanning, and data evaluation could be performed in &lt;2 h.

Results: Approximately 80 ng of DNA was obtained from 200-mg stool samples. No inhibition of the PCR by remaining impurities from stool was observed. Mutation detection was possible in 1000-fold excess of wild-type sequence. Discrimination ratios between the mutations were &gt;19 as demonstrated by hybridization with tumor cell line DNA. Stool samples (n = 26) were analyzed in parallel with PNA-PCR, restriction assay for K-ras codon 12 mutations, sequencing, and hybridization to the biochip. Nine mutations were found by hybridization, all confirmed by sequencing. PNA-PCR alone leads to an overestimation of mutations because suppression of the wild type is not effective enough with high concentrations of wild-type DNA. The restriction assay found only four mutations.

Conclusions: The K-ras biochip is well suited for fast mutation detection from stool in colorectal cancer screening.

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.

Early diagnosis for colorectal cancer in China

AIM

To review the present studies on early diagnosis of colorectal cancer.

METHODS

The detective rate for early cancer is 1.7%-26.1% based on various statistical data, with much higher detective rate in endoscopy. Since early cancer means invasion involved in the mucosa or submucosa, the diagnosis can only be made when the invasive depth is identified. Pathological tissue materials from both surgical operation or endoscopic resection are suitable for early cancer evaluation.

RESULTS

Incidence of polyp malignancy is 1.4%-20.4%. The various constitutive proportion of polyps may explain the different rates. Malignant incidence is higher in adenomatous polyps, that for villous polyps can reach 21.3%-58.3%. Type II early stage of colorectal carcinoma is rarely reported in China. It is shown that majority of them were not malignant, most of type IIa being adenoma or hyperplasia, and IIb being inflammatory and IIc might be the isolated ulcers. The occurrence of malignancy of type II is far lower than that of polypoid lesion. In China, the qualitative diagnosis and classification of neoplasm generally adopted the WHO standard, including surgical excision or biopsies. There is impersonal evaluation between colorectal pre-malignancy and cancer. The former emphasizes the dysplasia of nuclei and gland, while the latter is marked with cancer invasion. Diagnosis of early stage colorectal cancer in endoscopy is made with too much caution which made the detective rate much lower. Mass screening for asymptomatic subjects and follow-up for high risk population are mainly used to find the early stage colorectal cancer in China. Fecal occult blood test is also widely made as primary screening test, galactose oxygenase test of rectal mucus (T antigen), fecal occult albumin test are also used. The detective rate of colorectal cancer is 24-36.5 per 105 mass population.

CONCLUSION

Although carcinoma associated antigen in blood or stool, microsatellite DNA instability for high risk familial history, molecular biology technology for stool oncogene or antioncogene, telomerase activity and exfoliative cytological examination for tumor marker, are utilized, none of them is used in mass screening by now.

Colorectal cancer risk: the impact of evidence of a field effect of carcinogenesis on blinded diagnosis using an anti-adenoma antibody test performed on colonoscopic effluent

To better define high-risk populations for colorectal cancer screening, we used anti-adenoma antibody Adnab-9, comparing colonic effluent and tissue field effects from 45 high-risk and 11 control patients. We included Adnab-9 binding at the tissue level to elucidate the impact of a field effect of carcinogenesis contributing to the outcome of the effluent binding test. In high-risk patients, 64% of the left-sided effluent samples were positive (P < 0.002); 67% showed a field effect (P < 0.006); 82% of combined tests were positive (P < 0.001), as compared to 9%, 18%, and 27% respectively, of controls. Adnab-9 binding correlates with increased colorectal cancer risk associated with a field effect of carcinogenesis.

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.

Persistence of tumor DNA in plasma of breast cancer patients after mastectomy

BACKGROUND

We investigated tumor DNA changes before and after mastectomy in the plasma of breast cancer patients with no disseminated disease and eventually investigated these changes' relationship to specific pathological parameters of the tumors.

METHODS

We studied 41 patients. DNA extracted from tumor and normal breast tissues, mononuclear blood cells, and plasma was used for molecular studies. Alterations in the microsatellite markers D17S855, D17S654, D16S421, TH2, D10S197, and D9S161, as well as point mutations in the p53 gene and aberrant methylation of p16(INK4a), were used to identify and characterize tumor and plasma DNA. A number of tumor clinicopathological parameters were analyzed in each patient.

RESULTS

We found that 18 (44%) of the 27 patients with alterations in tumor DNA presented the same plasma DNA alteration before mastectomy, and persistence of the same molecular features was detected in plasma DNA 4 to 6 weeks postmastectomy in 8 (19.5%) patients. Patients with vascular invasion, more than three lymph node metastases, and higher histological grade at diagnosis displayed plasma DNA after mastectomy with a significant difference.

CONCLUSIONS

Persistence of plasma DNA with features of tumor DNA may be present after mastectomy in breast cancer patients, and its relation to bad-prognosis histological parameters may suggest undetectable micrometastatic disease.

The case for population-based screening for colorectal cancer

Screening for colorectal cancer is commanding increasing attention. Other cancer screening programmes have been a part of public consciousness for some time, but, until recently, colorectal cancer screening has remained in the background. Fuelled by new research, market opportunities and increased recognition of individual risk, screening for colorectal cancer is becoming a recommended procedure, but controversy about how best to implement widespread screening remains.

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.

Advanced diagnostic methods in oral and maxillofacial pathology. Part I: molecular methods

The practice of pathology is currently undergoing significant change, in large part due to advances in the analysis of DNA, RNA, and proteins in tissues. These advances have permitted improved biologic insights into many developmental, inflammatory, metabolic, infectious, and neoplastic diseases. Moreover, molecular analysis has also led to improvements in accuracy of disease diagnosis and classification. It is likely that, in the future, these methods will increasingly enter into the day-to-day diagnosis and management of patients. The pathologist will continue to play a fundamental role in diagnosis and will likely be in a pivotal position to guide the implementation and interpretation of these tests as they move from the research laboratory into diagnostic pathology. The purpose of this 2-part series is to provide an overview of the principles and applications of current molecular biologic and immunologic tests. Part I will discuss the biologic fundamentals of DNA, RNA, and proteins and the methods that are currently available or likely to become available to the pathologist in the next several years for their isolation and analysis in tissue biopsies.

Genetic heterogeneity in saliva from patients with oral squamous carcinomas: implications in molecular diagnosis and screening

We performed microsatellite analysis at chromosomal regions frequently altered in head and neck squamous carcinoma on matched saliva and tumor samples from 37 patients who had oral squamous carcinoma. The results were correlated with the cytologic findings and traditional clinicopathologic factors to assess the diagnostic and biological potential of these markers. Our data showed that 18 (49%) of the saliva samples and 32 (86%) of the tumors had loss of heterozygosity (LOH) in at least one of the 25 markers studied. In saliva, the combination of markers D3S1234, D9S156, and D17S799 identified 13 (72.2%) of the 18 patients with LOH in saliva (P < 0.001). For tumors, markers D3S1234, D8S254, and D9S171 together identified 27 (84.3%) of the 32 tumors with LOH at any of the loci tested (P < 0.001). Eleven (55%) of the 20 saliva samples with cytologic atypia and seven (35%) of the 17 specimens without atypia had LOH. Significant correlation between LOH in tumor at certain markers and smoking and alcohol use was found. Our results indicate that: 1) epithelial cells in saliva from patients with head and neck squamous tumorigenesis provide suitable material for genetic analysis; 2) combined application of certain markers improves the detection of genetic alteration in these patients; 3) clonal heterogeneity between saliva and matching tumor supports genetic instability of the mucosal field in some of these patients; and 4) LOH at certain chromosomal loci appears to be associated with smoking and alcohol consumption.

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.

Detection of N-Ras codon 61 mutations in subpopulations of tumor cells in multiple myeloma at presentation

Activating point mutations in codons 12, 13, or 61 of the K-ras and N-ras genes have been reported to occur in up to 40% of patients with multiple myeloma at presentation. In a study of 34 presentation myeloma cases using a sensitive polymerase chain reaction-restriction fragment length polymorphism strategy on enriched tumor cell populations, the present study detected N-ras codon 61 mutation-positive cells in all patients. Quantitative plaque hybridization using allele-specific oligonucleotide probes showed that in the majority of patients, ras mutation-positive cells comprise only a subpopulation of the total malignant plasma cell compartment (range, 12%-100%). Using clonospecific point mutations in the 5' untranslated region of the BCL6 gene to quantitate clonal B cells in FACS-sorted bone marrow populations from 2 patients, the representation of ras mutation-positive cells was independent of immunophenotype. These observations imply that mutational activation of N-ras codon 61 is a mandatory event in the pathogenesis of multiple myeloma; such mutations provide a marker of intraclonal heterogeneity that may originate at an earlier ontologic stage than immunophenotypic diversification of the malignant B cell clone.

Colorectal cancer screening

Colorectal cancer causes significant morbidity and mortality in the United States. The incidence of colorectal cancer increases at age 50, approximately. Risk factors that have been identified include a personal history of colorectal cancer or adenomas, a family history of colon cancer or adenomas, inherited colorectal cancer syndromes, and long standing inflammatory bowel disease. Several screening tests have been developed for colorectal cancer prevention. Surveillance strategy is based on an individual's colorectal cancer risk. This article reviews fecal occult blood testing, flexible sigmoidoscopy, colonoscopy, barium enema, and genetic testing.

Biomarkers in disease and health

Biomarkers have considerable potential in aiding the understanding of the relationship between diet and disease or health. However, to assess the role, relevance and importance of biomarkers on a case by case basis it is essential to understand and prioritise the principal diet and health issues. In the majority of cases, dietary compounds are only weakly biologically active in the short term, have multiple targets and can be both beneficial and deleterious. This poses particular problems in determining the net effect of types of foods on health. In principle, a biomarker should be able to contribute to this debate by allowing the measurement of exposure and by acting as an indicator either of a deleterious or of an enhanced health effect prior to the final outcome. In this review, the examples chosen - cancer (stomach, colon/rectal, breast); coronary heart disease and osteoporosis - reflect three major diet-related disease issues. In each case the onset of the disease has a genetic determinant which may be exacerbated or delayed by diet. Perhaps the most important factor is that in each case the disease, once manifest, is difficult to influence in a positive way by diet alone. This then suggests that the emphasis for biomarker studies should focus on predictive biomarkers which can be used to help in the development of dietary strategies which will minimise the risk and be of greater benefit.

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.