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

Screening for colon cancer

Colorectal cancer screening reduces mortality in individuals 50 years and older. Each of the screening tests currently available has advantages and limitations, and there is no consensus as to which test or combination of tests is best. What is clear, however, is that the rates of colorectal cancer screening remain low. This review summarizes the clinical evidence supporting colorectal cancer screening in the average risk population and in high risk groups, discusses the advantages and disadvantages of the available screening tests, outlines the currently recommended guidelines for screening based on risk category, and discusses new and emerging technologies for colorectal cancer screening.

Detection of Mononucleotide Repeat Sequence Alterations in a Large Background of Normal DNA for Screening High-Frequency Microsatellite Instability Cancers

PURPOSE

Mutations in mononucleotide repeat sequence (MRS) are good indicators of high-frequency microsatellite instability (MSI-H) cancers, but it has been a challenge to detect such mutations in a large background of wild-type DNA; as in this setting, PCR errors often generate false positive mutant alleles. In this study, we developed a general strategy, referred to as probe clamping primer extension-PCR (PCPE-PCR), to detect MRS alterations in a large background of wild-type DNA.

EXPERIMENTAL DESIGN

In PCPE-PCR, genomic DNA is first subjected to PCPE, in which mutant single-strand DNA molecules are preferentially produced. Next, genomic DNA is removed to enrich for the mutant DNA fraction. Thereafter, PCR is carried out using the remaining single-strand DNA molecules as templates. Finally, the PCR products are analyzed to reveal the MSI-H status. In this study, the sensitivity of this new method was first examined by spiking mutant DNA into wild-type DNA at specific ratios followed by studying whether this method is applicable to fecal DNA testing.

RESULTS

We showed that PCPE-PCR could detect both mutated BAT26 and transforming growth factor-beta-RII (A)10 markers in the presence of 500-fold excess of normal DNA and that as few as three copies of mutated DNA could be detected. In addition, we showed that this technology could detect MSI-H colorectal cancer by fecal DNA analysis.

CONCLUSION

PCPE-PCR is sensitive. In addition, PCPE-PCR is simple and amendable to a cost-effective and high-throughput screening operation. This technology may be applicable to noninvasive screening of MSI-H cancer.

Comparative evaluation of a new bedside faecal occult blood test in a prospective multicentre study

BACKGROUND

Faecal occult blood testing is an established method of colorectal neoplasia screening. Guaiac-based tests are limited by poor patient compliance, low sensitivity, specificity and positive predictive value. Newer immunochemical-based tests, accurate but tedious, require a well-established laboratory set up. There is need for simpler immunochemical tests that can be performed at the out-patient clinic.

AIM

To compare the performance characteristics of a new bedside immunological test strip device with a sensitive Guaiac-based and established immunochemical test for detection of faecal occult blood in patients undergoing colonoscopy.

METHODS

A total of 389 consecutive patients from four centres who were referred for colonoscopy also provided the stool samples for detection of occult blood without dietary restrictions. Stool tests performed were (i) Guaiac-based, (ii) immunochemical enzyme-linked immunosorbent assay and (iii) bedside immunochemical strip test.

RESULTS

At the optimal threshold level, the sensitivity and specificity of the beside immunochemical strip test for detection of significant colorectal neoplasia (adenomas >1.0 cm and carcinomas) were 60% and 95%, respectively.

CONCLUSIONS

This bedside immunochemical strip test proved to be a simple, convenient, non-cumbersome and accurate tool with similar performance characteristics for detection of any bleeding lesion including colorectal neoplasia when compared with an established immunochemical faecal occult blood test.

Prospective multicenter evaluation of fecal tumor pyruvate kinase type M2 (M2-PK) as a screening biomarker for colorectal neoplasia

Proliferating cells, particularly the tumor cells, express a dimeric isoenzyme of pyruvate kinase, termed M2-PK. It's a direct target of several oncoproteins; the determination of fecal tumor pyruvate kinase type M2 (M2-PK) might be another promising tool for colorectal cancer (CRC) screening. In this study, we have evaluated fecal M2-PK as a screening biomarker for colorectal neoplasia. It was compared against fecal occult blood (FOB) and colonoscopy. Three hundred and seventeen consecutive subjects from 4 different centers were included. Stool specimens were collected before purgation, processed appropriately and were tested for FOB and quantitatively analyzed for M2-PK. Colonoscopies were performed by experienced endoscopists who were unaware of fecal assay results. At cutoff value of 4 U/ml, fecal M2-PK assay had a sensitivity, specificity, PPV and NPV of 81.1, 86.7, 71.1 and 61.9% respectively for diagnosing CRC whereas FOBT showed a sensitivity of 36.5%, specificity of 92.2%, PPV of 72.9% and NPV of 71.5% for CRC. Such low specificity of fecal M2-PK will lead to unacceptably high number of false positives if it is used for mass CRC screening, leading to unindicated colonoscopies with its associated inconveniences, risks and costs. CRC screening test must have high specificity; a high sensitivity is not as vital. To conclude, M2-PK was found to be a poor screening biomarker for CR neoplasia in a subject population at above average risk based on its prospective comparison with colonoscopy. These marginal performance characteristics do not permit its use as a screening tool for CR neoplasia in present clinical settings.

Sedation and analgesia for gastrointestinal endoscopy during pregnancy

Endoscopy during pregnancy raises the unique issue of fetal safety. Endoscopic medications comprise a significant component of fetal risks from endoscopy. Before endoscopy, the gastroenterologist or anesthesiologist should evaluate the potential fetal risks of sedation and analgesia, identify any contraindications to endoscopy, stabilize the maternal medical status as necessary, and correct maternal hypoxia or hypotension. The mother should be informed about the potential teratogenic risks of endoscopic medications during pregnancy. Patients who receive sedation and analgesia should be monitored during endoscopy by continuous electrocardiography, continuous pulse oximetry, and intermittent sphygmomanometry, as well as by the pulse and respiratory rate. General principles of sedation and analgesia during pregnancy include use of the minimal effective dose, avoidance of unnecessary medications, and preferable use of Food and Drug Administration category B medications.

Detection and quantification of mutations in the plasma of patients with colorectal tumors

The early detection of cancers through analysis of circulating DNA could have a substantial impact on morbidity and mortality. To achieve this goal, it is essential to determine the number of mutant molecules present in the circulation of cancer patients and to develop methods that are sufficiently sensitive to detect these mutations. Using a modified version of a recently developed assay for this purpose, we found that patients with advanced colorectal cancers consistently contained mutant adenomatous polyposis coli (APC) DNA molecules in their plasma. The median number of APC DNA fragments in such patients was 47,800 per ml of plasma, of which 8% were mutant. Mutant APC molecules were also detected in >60% of patients with early, presumably curable colorectal cancers, at levels ranging from 0.01% to 1.7% of the total APC molecules. These results have implications for the mechanisms through which tumor DNA is released into the circulation and for diagnostic tests based on this phenomenon.

Discrimination of Breast Cancer by Anti-Malignin Antibody Serum Test in Women Undergoing Biopsy

PURPOSE

The anti-malignin antibody serum (AMAS) test (Oncolab, Boston, MA) has been reported as 97% sensitive and 95% specific for malignancies. To objectively assess accuracy of this test for discrimination of breast cancer, we studied a series of women undergoing core breast biopsy.

SUBJECTS AND METHODS

Seventy-one core-needle breast biopsies were classified as malignant, suspicious, or benign by two independent pathologists blinded to AMAS results. Corresponding sera were read as AMAS positive, negative, or borderline by criteria used by Oncolab and also using criteria derived from receiver-operator curves based on values for slow (S-tag), fast (F-tag), and their difference (Net-tag) antibody reported by Oncolab. We calculated sensitivity and specificity and analyzed distributions by Fisher's exact test.

RESULTS

Biopsies were read as 42 (59%) benign, 12 (17%) suspicious, and 17 (24%) malignant. By Oncolab criteria, sensitivity (59%) and specificity (62%) were maximized by pooling suspicious with malignant and AMAS borderline with positive (P = 0.098). Receiver-operator curves showed best sensitivity (62%) and specificity (69%) for the criterion AMAS positive if Net-Tag > 135 microg/mL or S-Tag > 220 microg/mL (P = 0.015).

CONCLUSIONS

The AMAS test discriminates suspicious and malignant from benign lesions, but sensitivity is insufficient to identify patients to be spared biopsy and false-positive rates are too high for population screening.

Detection in fecal DNA of colon cancer-specific methylation of the nonexpressed vimentin gene

BACKGROUND

Increased DNA methylation is an epigenetic alteration that is common in human cancers and is often associated with transcriptional silencing. Aberrantly methylated DNA has also been proposed as a potential tumor marker. However, genes such as vimentin, which are transcriptionally silent in normal epithelium, have not until now been considered as targets for cancer-associated aberrant methylation and for use as cancer markers.

METHODS

We applied methylation-specific polymerase chain reaction to the vimentin gene, which is transcriptionally silent in normal colonocytes, and compared methylation of vimentin exon 1 in cancer tissues and in fecal DNA from colon cancer patients versus control samples from healthy subjects.

RESULTS

Vimentin exon-1 sequences were unmethylated in 45 of 46 normal colon tissues. In contrast, vimentin exon-1 sequences were methylated in 83% (38 of 46) and 53% (57 of 107) of tumors from two independently collected groups of colon cancer patients. When evaluated as a marker for colon cancer detection in fecal DNA from another set of colon cancer patients, aberrant vimentin methylation was detected in fecal DNA from 43 of 94 patients, for a sensitivity of 46% (95% confidence interval [CI] = 35% to 56%). The sensitivity for detecting stage I and II cancers was 43% (26 of 60 case patients) (95% CI = 31% to 57%). Only 10% (20 of 198 case patients) of control fecal DNA samples from cancer-free individuals tested positive for vimentin methylation, for a specificity of 90% (95% CI = 85% to 94%).

CONCLUSIONS

Aberrant methylation of exon-1 sequences within the nontranscribed vimentin gene is a novel molecular biomarker of colon cancer and can be successfully detected in fecal DNA to identify nearly half of individuals with colon cancer.

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.

Noninvasive testing for colorectal cancer: a review

OBJECTIVES

Colorectal cancer (CRC) is the second leading cause of cancer-related death in the United States. Endoscopic screening is now in favor and its use is increasing, but overall participation rates are poor. A substantial percentage of the population will likely continue to resist endoscopic screening. As such, a noninvasive biomarker for the early detection of CRC remains a priority. Herein, we (i) review the currently available noninvasive screening markers for the early detection of CRC, (ii) discuss newer markers that have undergone preliminary testing, and (iii) introduce and explain potentially promising markers of the future.

METHODS

The published literature on markers for early detection of CRC was identified using a MEDLINE/PubMed search with secondary review of cited publications.

RESULTS

Noninvasive testing for CRC is most advanced in testing for stool fecal occult blood, globin, or DNA mutations. Study of abnormal mucins has also been explored. Research for serum-based markers is just beginning and includes serum proteomics, nuclear matrix proteins, and serum DNA testing.

CONCLUSIONS

Serial guaiac-based fecal occult blood testing (FOBT) is simple, inexpensive, and proven effective at reducing mortality from CRC. Immunochemical fecal occult blood tests facilitate compliance and offer improved specificity, but at increased cost in comparison to FOBT. Fecal DNA testing may provide enhanced sensitivity for detection of CRC in comparison with FOBT, but its high cost limits its use for generalized screening. Rectal mucin testing requires additional evaluation to determine its sensitivity and specificity in comparison with guaiac-based FOBT. Serum tests, such as proteomics, nuclear matrix proteins, and serum DNA, are still in their infancy, but remain a hope for the future.

The stool DNA test: an emerging technology in colorectal cancer screening

The stool DNA test is considered an emerging technology in screening for colorectal cancer. The stool DNA test detects DNA markers which are shed from cells of premalignant adenomas and cancers into the stool. Potentially, both preclinical and clinical colorectal cancer may be detected. Panels of multiple DNA markers are used to ensure a high sensitivity for colorectal cancer. In this article, several advantages of the stool DNA test (compared with current colorectal cancer screening methods) are discussed. The stool DNA test may be more patient-friendly and has a higher degree of sensitivity and specificity for colorectal cancer. No bowel or dietary preparation is required and the test is noninvasive. The stool DNA test screens the entire colon and may detect some other types of cancers proximal to the colon. In the future, there may be potential to use the stool DNA test to screen for aerodigestive cancers (lung, esophageal, gastric, and pancreatic), in addition to colorectal cancer. An improved noninvasive screening test would help allocate colonoscopy resources to those patients who would benefit the most. Colorectal cancer screening cost-effectiveness may also be improved. Some limitations of the stool DNA test include the need for clinical studies in average-risk populations and marker refinement. An automated testing system may help reduce costs and turnaround times. Despite recognized limitations, the stool DNA test is a promising new diagnostic tool with the potential to improve effectiveness of colorectal cancer screening.

Dark lumen MR colonography based on fecal tagging for detection of colorectal masses: accuracy and patient acceptance

BACKGROUND

Magnetic resonance colonography (MRC) with fecal tagging has recently been investigated in clinical studies for the detection of polyps. We assessed fecal tagging MRC in a field trial.

METHODS

Forty-two patients in a private gastroenterologic practice underwent MRC with barium-based fecal tagging (150 mL of 100% barium at each of 6 main meals before MRC) and conventional colonoscopy. Diagnostic accuracy of MRC and patient acceptance were assessed and compared with the respective results of conventional colonoscopy.

RESULTS

Eighteen percent of all MRC examinations showed a remaining high stool signal in the colon that impeded a reliable inclusion or exclusion of polyps. On a lesion-by-lesion basis, sensitivities for polyp detection were 100% for polyps larger than 2 cm (n = 1), 40% for polyps between 10 and 19 mm, 16.7% for polyps between 6 and 9 mm, and 9.1% for polyps smaller than 6 mm. The main reason for the low acceptance of MRC was the barium preparation, which was rated worse than the bowel cleaning procedure with conventional colonoscopy.

CONCLUSION

MRC with fecal tagging must be further optimized. The large amount of barium resulted in poor patient acceptance, and barium according to this protocol did not provide sufficient stool darkening. Other strategies, such as increasing the hydration of stool, must be developed.

Colorectal cancer screening: prospects for molecular stool analysis

Colorectal cancer is common. As many patients present with advanced disease, an effective screening test would have substantial clinical benefits. Recent progress in understanding the biology of colorectal cancer (and of cancer cells in general) has led to possible new approaches to screening. In particular, there are prospects of developing tests based on analysis of stool, which promise improved accuracy, safety, affordability and patient compliance.

From Colonic Polyps to Colon Cancer: Pathophysiology, Clinical Presentation, and Diagnosis

Epidemiologists, basic researchers, clinicians, and public health administrators unite! Develop and implement a simple, safe, and effective preventive and screening test for colon cancer. The public will willingly and enthusiastically accept such a test. Many thousands of lives are at stake every year.

Non-invasive detection of colorectal tumours by the combined application of molecular diagnosis and the faecal occult blood test

The treatment of early-stage tumours decreases the overall mortality of colorectal tumour patients. In this retrospective study we determined the sensitivity and the specificity of the faecal occult blood test (FOBT) and the molecular diagnosis (MD). We analysed 57 stool samples from patients with colorectal carcinomas for the presence of occult blood using a standard FOBT and for alterations in the three different tumour relevant markers APC, BAT26 and L-DNA. Stool samples from 44 control donors were analysed to determine the specificity of the applied methods. Twenty-nine (51%; 95% confidence interval (CI): 38-63%) stool samples of the cancer patients gave positive FOBT results. Thirty-seven (65%; CI: 52-76%) samples showed alterations in at least one DNA marker. Sixteen (28%) samples were positive only in the FOBT, and 24 (42%) samples showed a positive result exclusively in MD. The combined application of both methods resulted in a sensitivity of 93% (CI: 83-97%) and an overall specificity of 89% (CI: 76-95%). The combined application of FOBT and MD resulted in an overall sensitivity, which could not be achieved by any of the methods alone and which is in the range of invasive diagnostic methods.

The pathophysiology, clinical presentation, and diagnosis of colon cancer and adenomatous polyps

A review of the pathophysiology, clinical presentation, and diagnosis of colon cancer and colonic polyps is important and timely. This field is rapidly changing because of breakthroughs in the molecular basis of carcinogenesis and in the technology for colon cancer detection and treatment. This article reviews colon cancer and colonic polyps, with a focus on recent dramatic advances, to help the pri-mary care physician and internist appropriately refer patients for screening colonoscopy and intelligently evaluate colonoscopic findings to reduce the mortality from this cancer.

Fecal DNA versus fecal occult blood for colorectal-cancer screening in an average-risk population

BACKGROUND

Although fecal occult-blood testing is the only available noninvasive screening method that reduces the risk of death from colorectal cancer, it has limited sensitivity. We compared an approach that identifies abnormal DNA in stool samples with the Hemoccult II fecal occult-blood test in average-risk, asymptomatic persons 50 years of age or older.

METHODS

Eligible subjects submitted one stool specimen for DNA analysis, underwent standard Hemoccult II testing, and then underwent colonoscopy. Of 5486 subjects enrolled, 4404 completed all aspects of the study. A subgroup of 2507 subjects was analyzed, including all those with a diagnosis of invasive adenocarcinoma or advanced adenoma plus randomly chosen subjects with no polyps or minor polyps. The fecal DNA panel consisted of 21 mutations.

RESULTS

The fecal DNA panel detected 16 of 31 invasive cancers, whereas Hemoccult II identified 4 of 31 (51.6 percent vs. 12.9 percent, P=0.003). The DNA panel detected 29 of 71 invasive cancers plus adenomas with high-grade dysplasia, whereas Hemoccult II identified 10 of 71 (40.8 percent vs. 14.1 percent, P<0.001). Among 418 subjects with advanced neoplasia (defined as a tubular adenoma at least 1 cm in diameter, a polyp with a villous histologic appearance, a polyp with high-grade dysplasia, or cancer), the DNA panel was positive in 76 (18.2 percent), whereas Hemoccult II was positive in 45 (10.8 percent). Specificity in subjects with negative findings on colonoscopy was 94.4 percent for the fecal DNA panel and 95.2 percent for Hemoccult II.

CONCLUSIONS

Although the majority of neoplastic lesions identified by colonoscopy were not detected by either noninvasive test, the multitarget analysis of fecal DNA detected a greater proportion of important colorectal neoplasia than did Hemoccult II without compromising specificity.

Improved methods for extracting RNA from exfoliated human colonocytes in stool and RT-PCR analysis

In order to diagnose colon cancer at an earlier, more localized stage, there is a need to develop diagnostic markers (genes) which can detect early patterns of gene expression in exfoliated colonocytes shed in the stool during routine screening for this disease. An RNA-based detection is more pertinent than either a DNA-based or a protein-based method as a screening procedure, but it has not been widely used as a cancer screen because of the difficulty of handling and stabilizing the RNA molecule. We describe a method that permits extraction of intact nondegraded total RNA from human colonocytes in stool and from normal and malignant colon tissues (which were employed for comparison with stool). Because it utilizes commercially available kits, this method is simpler than other published methods and does not require isolation of messenger (m)RNA, thereby reducing the chances of contaminating the preparations with degrading nucleases, and even a small amount of isolated total RNA can be adequately reverse transcribed, making high-quality copy (c) DNA. This is followed by PCR (either qualitative end point or semiquantitative real-time) using colon cancer-specific gene primers. By routinely and systematically being able to perform quantitative gene expression measurements on noninvasive samples, the goal of this pilot work is to lay the groundwork for conducting a large clinical study to identify groups of selected genes whose expression is consistently altered at an early stage in the neoplastic process. Such work will permit noninvasive monitoring of at-risk patients through the analysis of their stool samples. Correct diagnosis will allow for surgical and/or other interventions before the tumor is well established and, thus, should decrease mortality from this preventable disease.

Challenges for Biomarkers in Cancer Detection

Cancer remains the leading cause of death in the United States. Biomarkers can be used to detect cancer in different stages, initiation, development, and progression. The desirable property and utility of a biomarker lie in its ability to provide an early indication of disease progression. Biomarkers should be easy to detect, measurable across populations, and useful for detection of cancer at an early stage, identification of high-risk individuals, detection of recurrence, or monitoring endpoints in intervention studies. Recent technological advances have helped develop noninvasive, sensitive, and specific biomarkers to detect cancer at early stages of the disease.

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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.

Prospective evaluation of fecal calprotectin as a screening biomarker for colorectal neoplasia

OBJECTIVES

Stool testing is a well established method of screening for colorectal neoplasia. Emerging data suggest that novel biomarkers may offer performance advantages over fecal occult blood. In this large, prospective study, we assessed fecal calprotectin (a leukocyte-derived protein) as a screening biomarker for colorectal neoplasia. Fecal calprotectin was directly compared to fecal hemoglobin (Hb) and colonoscopy as the existing criterion standards for stool screening and structural evaluation, respectively.

METHODS

Subjects included colonoscopy patients with a personal history of colorectal neoplasia, family history of colorectal cancer, or iron deficiency anemia. Stool specimens were collected before purgation, processed appropriately, and quantitatively analyzed for calprotectin (Nycomed Pharma, Oslo, Norway) and for Hb (Mayo Medical Laboratories, Rochester, MN) by masked technicians. Colonoscopies were performed by experienced endoscopists without prior knowledge of the fecal assay results.

RESULTS

Among 412 subjects, 97 (24%) subjects had one or more colorectal neoplasms (including three with adenocarcinomas). Fecal calprotectin levels did not differ significantly between subjects with versus subjects without colorectal neoplasms (p = 0.33). Neither tumor number (p = 0.85) nor tumor size (p = 0.86) significantly influenced the observed fecal calprotectin concentrations. Estimates of the sensitivity, specificity, and positive and negative predictive values of fecal calprotectin for any colorectal neoplasms were 37%, 63%, 23%, and 76%, respectively. Comparable performance estimates for fecal Hb were 3%, 97%, 27%, and 77%, respectively.

CONCLUSIONS

In this cohort of colonoscopy patients at above average risk, fecal calprotectin was a poor screening biomarker for colorectal neoplasia. Further investigation of tumor-derived, rather than blood-based, biomarkers may be a more rewarding approach to stool screening for colorectal neoplasia.

Transforming single DNA molecules into fluorescent magnetic particles for detection and enumeration of genetic variations

Many areas of biomedical research depend on the analysis of uncommon variations in individual genes or transcripts. Here we describe a method that can quantify such variation at a scale and ease heretofore unattainable. Each DNA molecule in a collection of such molecules is converted into a single magnetic particle to which thousands of copies of DNA identical in sequence to the original are bound. This population of beads then corresponds to a one-to-one representation of the starting DNA molecules. Variation within the original population of DNA molecules can then be simply assessed by counting fluorescently labeled particles via flow cytometry. This approach is called BEAMing on the basis of four of its principal components (beads, emulsion, amplification, and magnetics). Millions of individual DNA molecules can be assessed in this fashion with standard laboratory equipment. Moreover, specific variants can be isolated by flow sorting and used for further experimentation. BEAMing can be used for the identification and quantification of rare mutations as well as to study variations in gene sequences or transcripts in specific populations or tissues.

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.

Use of exfoliated cells from target tissues to predict responses to bioactive food components

A host of bioactive food components have been proposed to promote health and reduce the risk of disease states. It is clear that not all individuals respond identically to these essential and nonessential food components. Genetic polymorphisms may influence absorption, metabolism and accumulation of bioactive food components, thereby influencing their actions in target tissues. Unfortunately, serum concentrations of bioactive food components may not correlate with tissue concentrations and may therefore under- or overestimate the response in target tissues. Exfoliated cells may be useful to assess the actions of nutrients in specific tissues. Although not extensively examined, evidence already suggests the usefulness of these cells in predicting changes in gene expression, DNA methylation, DNA damage, protein expression and accumulation of dietary components. Although there are limitations on the collection of exfoliated cells, the inaccessibility of tissues they can represent raises intriguing possibilities for their ability to predict the outcome of nutritional intervention studies.

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.

The use of denaturing high-performance liquid chromatography (DHPLC) for the analysis of genetic variations: impact for diagnostics and pharmacogenetics

Over the past five years, denaturing high-performance liquid chromatography (DHPLC) has emerged as one of the most versatile technologies for the analysis of genetic variations. With the benefit of novel polymer chemistries used for separation, the accuracy, sensitivity, and the throughput of DHPLC for DNA and RNA analysis have greatly improved. DHPLC has been adopted in many laboratories for the screening of mutations and single-nucleotide polymorphisms (SNPs). The ability of DHPLC to detect known and unknown mutations simultaneously has put this technology at the forefront of genetic analysis for a wide variety of diseases. In addition, the high sensitivity of DHPLC combined with the accuracy of the heteroduplex analysis has allowed the development of applications beyond the scope of traditional sequencing or genotyping, e.g., the early detection of cancer. This article reviews the methods, which made DHPLC a widely used tool for diagnosis in molecular genetics and pharmacogenetics. The article provides an overview of current applications in these fields and points to novel applications in areas like epigenetics and the analysis of heteroplasmic mitochondrial DNA, in which DHPLC is becoming the leading technology.

Colon cancer during pregnancy

The medical community should become mobilized to diagnose colon cancer earlier in pregnancy to improve prognosis. The primary care physician or obstetrician should refer the pregnant patient with significant gastrointestinal complaints to the gastroenterologist for evaluation. Likewise, the gastroenterologist should be prepared to perform sigmoidoscopy, preferably without endoscopic medications, for significant lower gastrointestinal symptoms such as persistent rectal bleeding. Sigmoidoscopy is particularly sensitive in identifying colon cancer in pregnant patients because their cancers are usually distal and within reach of the sigmoidoscope.

The fetal safety and clinical efficacy of gastrointestinal endoscopy during pregnancy

More than 12,000 pregnant patients in the United States per annum have conditions that are normally evaluated by EGD. More than 6000 pregnant patients in the United States per annum have conditions that are normally evaluated by sigmoidoscopy or colonoscopy. About one thousand more have symptomatic choledocholithiasis during pregnancy, which is a strong indication for endoscopic sphincterotomy in nonpregnant patients. Endoscopy during pregnancy raises the unique issue of fetal safety. Endoscopic medications comprise a significant component of fetal endoscopic risks. Safety of EGD during pregnancy has been examined in a case-controlled study of 83 patients, a mailed survey of 73 patients, and 28 case reports. Safety of sigmoidoscopy during pregnancy has been examined in a case-controlled study of 46 patients, a mailed survey of 13 patients, and 10 case reports. Safety of therapeutic ERCP during pregnancy has been analyzed in studies of 23, 10, 6, and 5 patients, and in 32 case reports. These studies suggested that EGD, sigmoidoscopy, and ERCP should be performed when strongly indicated: EGD for significant upper gastrointestinal bleeding, sigmoidoscopy for nonhemorrhoidal rectal bleeding, and ERCP for symptomatic choledocholithiasis when sphincterotomy is contemplated. PEG and colonoscopy are currently considered experimental during pregnancy because of insufficient data on fetal safety. Several cases of PEG and colonoscopy were successfully performed during pregnancy. Performance of endoscopy during pregnancy should increase with further technical refinements, and greater awareness of procedure safety.

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.

Identification of colon cancer patients by molecular diagnosis

The important causal role of DNA alterations in cancer development implies that tumor specific DNA mutations might serve as ideal parameters in cancer diagnosis. In particular the detection of mutations in fecal DNA might complement the current methods for the early diagnosis of colorectal tumors. Over the last 10 years many studies have proven the usefulness and the feasibility of the fecal DNA analysis in the diagnosis of colon tumors. Technical difficulties have circumvented the clinical application and the broad screening by molecular diagnosis. Recent methodological proceedings together with the promising outcomes of first multi-target studies have put a diagnostic stool-based DNA test for colorectal tumors within close reach.

The role of sigmoidoscopy and colonoscopy in the diagnosis and management of lower gastrointestinal disorders: endoscopic findings, therapy, and complications

Flexible sigmoidoscopy and colonoscopy have revolutionized the clinical management of colonic diseases. Colonoscopy is a highly sensitive and specific test. Colonic diseases often produce characteristic colonoscopic findings, as well as characteristic histologic findings, as identified in colonoscopic biopsy or polypectomy specimens. Colonoscopy is relatively safe, with a low incidence of serious complications, such as colonic perforation, hemorrhage, cardiopulmonary arrest, or sepsis. Colonoscopy is becoming more important clinically because of more widespread use of screening colonoscopy for colon cancer, application of therapeutic colonoscopy, and exciting new technical improvements.

Molecular screening for colon cancer in inflammatory bowel disease

Prophylactic colectomy is an established method of bowel cancer prevention in high-risk patients such as familial adenomatosis polyposis coli (FAP) and hereditary non-polyposis colorectal cancer (HNPCC) kindreds, as well as in patients with longstanding ulcerative colitis or Crohn's disease. The decision to perform such a major procedure cannot be made lightly, and issues of timing are important. In inflammatory bowel disease (IBD), the trigger to carry out colectomy usually relates to detection of dysplasia, well recognized to be a premalignant lesion. Screening methods are aimed at detection of precursor lesions or clinically occult malignancies. In current clinical practice, such screening methods are either resource intensive (e.g. colonoscopy and biopsy) or of low sensitivity and specificity (e.g. faecal occult blood testing). We discuss the development of screening techniques based upon molecular technologies and the limitations engendered by our incomplete understanding of the natural history and molecular biology of colorectal neoplasia in IBD.

Colonoscopy as a screening test for colorectal cancer in average-risk individuals

Screening for colorectal cancer has become the standard of care and is currently recommended by most major health organizations, including the American Cancer Society. Randomized controlled trials using fecal occult blood testing as the screening strategy have shown a reduction in mortality due to colorectal cancer. However, colorectal cancer differs from other cancers in that a variety of screening tests have been approved and recommended by experts. The advantages and disadvantages of different screening tests have been the subject of intense debate. Colonoscopy has theoretical advantages over other screening tests, including direct visualization of the entire colon and, more importantly, removal of precancerous adenomatous lesions. This review discusses the advantages and disadvantages of colonoscopy as a screening test for colorectal cancer with regard to efficacy, cost-effectiveness, and patient compliance.

Screening for carcinoma of the colon: current views

Colorectal cancer (CRC) is the second commonest cause of death from malignancy in the UK. Sixty per cent of patients die within 5years of diagnosis because the cancer usually has metastasized before presentation. Increased public awareness of symptoms, the 2-week rule for patients with suspected cancer together with more specialized training for colorectal surgeons and the use of adjuvant chemotherapy and radiotherapy may improve survival rates. However, without a more radical approach, it seems unlikely that more than 50% of patients with this disease will be cured. The cause of CRC is unknown, and although dietary factors play a part in its pathogenesis and certain drugs may inhibit the polyp cancer sequence, primary prevention is not possible at present. Only population screening offers a real opportunity to impact on the mortality of this disease, which in the UK kills roughly one person in fifty.

Detection of proximal colorectal cancers through analysis of faecal DNA

Detection of mutations in faecal DNA represents a promising, non-invasive approach for detecting colorectal cancers in average-risk populations. One of the first practical applications of this technology involves the examination of microsatellite markers in sporadic cancers with mismatch-repair deficiencies. Since such cancers nearly always occur in the proximal colon, this test might be useful as an adjunct to sigmoidoscopy, which detects only distal colorectal lesions. We report here the first in-depth analysis of faecal DNA from patients with proximal cancers to determine the feasibility, sensitivity, and specificity of this approach. Using a sensitive method for microsatellite mutation detection, we found that 18 of 46 cancers had microsatellite alterations and that identical mutations could be identified in the faecal DNA of 17 of these 18 cases.