DNA bar code: screening methods of colorectal cancer.
To earn CEUs, see test on page 22.
Upon completion of this article, the reader will be able to:
1. Cite current risk statistics for the development of colorectal cancer.
2. Describe the progression of benign lesions to neoplastic lesions.
3. Describe the process of mutation involved in hereditary colorectal cancer.
4. Explain why screening tests are clinically important to the diagnosis of colorectal cancer.
5. Examine the reasons for both false positive and false negative fecal occult blood tests.
6. Explain the use of screening tests based on neoplastic markers in colonocytes.
7. Differentiate between colonoscopy, flexible sigmoidoscopy, double-contrast barium enema, and "virtual colonoscopy" in colorectal cancer screening.
8. Describe how molecular markers can be used in the detection of malignant cells.
9. State the current recommended use for serum CEA levels.
10. Summarize the potential use of proteomics in colorectal cancer diagnosis.
Colorectal cancer (CRC) is the third most common cause of malignancy-related death globally. One million people are diagnosed with CRC each year and greater than 500,000 deaths from CRC occur worldwide annually. (1,2) In the developed world, the lifetime risk for colorectal cancer is ~4% to 6%. (2,3) Although routine screening has reduced mortality rates over past decades by ~15%, the potential benefit of early detection has not been fully realized. (4,5) Colorectal cancer is currently detected by a variety of image- and stool-based screening methods, such as the fecal occult blood test (FOBT), double-contrast barium enema, and colonoscopy. Despite the availability of these screens, only half of the population over the age of 50 have undergone the recommended screening. (2) In the present article, we discuss the current screening recommendations, discuss their effectiveness, and present recent progress in applying DNA-based markers for colorectal cancer to patient populations. These molecular markers, detected in both serum and stool, may potentially be used to identify colorectal cancer without the risk, discomfort, and expense of traditional methods in an effort to improve patient outcome.
Pathogenesis of colorectal cancer
Sporadic colorectal cancer has been characterized as a progression from benign overgrowth, the accumulation of genetic mutations, to malignant carcinoma (see Figure 1). Polyps, which are localized overgrowth of the lining of the colon that protrude into the gut lumen, are benign lesions that may progress to colon cancer. Polyps are broadly classified as neoplastic (adenomatous) or non-neoplastic, with the vast majority (90%) being benign (non-neoplastic). In the genetic model known as the adenoma-carcinoma sequence shown in Figure 1, mutations in the adenomatous polyposis coli gene (APC) and Kirsten rat sarcoma 2 viral oncogene homolog (K-ras) are associated with disease stage progression. It is proposed that APC mutates early in this process, leading to hyperproliferation and adenoma formation. As epithelial cells proliferate, DNA methylation becomes dysregulated resulting in mutation of additional genes, such as K-ras, and the formation of 'intermediate' adenomas. In more severe disease, loss of tumor-suppressor genes, such as SMAD2/4, eventually leads to the formation of 'late' adenomas. Finally, the loss of the cell cycle regulatory gene, TP53, causes the formation of carcinomas. (6)
[FIGURE 1 OMITTED]
Once carcinomas reach the submucosa, they can spread throughout the body through the lymphatics and blood vessels resulting in metastasis. The majority of adenocarcinomas originate in the cecum (38%), and the sigmoid colon (29%). (3) Lesions of the proximal colon often protrude into the gut lumen and are associated with vague symptoms that often go unnoticed. In contrast, carcinomas of the distal colon tend to grow as circular lesions that encompass the entire circumference of the colon. As these lesions expand, they cause narrowing of the gut lumen, which leads to earlier presentation with symptoms such as constipation or diarrhea. Since these lesions bleed and are proximal to the rectum, they typically cause noticeable blood loss in the stool and present earlier in the course of disease. Despite earlier presentation, distal colon carcinomas are often more infiltrative at the time of diagnosis than proximal lesions and have a poorer prognosis.
Approximately 10% to 15% of colorectal cancers involve inherited genetic mutations. (3) There are several different forms of hereditary (familial) colorectal cancers, the most common of which are familial adenomatous polyposis (FAP) and hereditary non-polyposis colorectal cancer (also known as Lynch syndrome). Both of these types of colorectal cancer strike patients at a younger age and progress from adenoma to carcinoma with very high frequency. Familial colorectal cancers are caused by a defined set of inherited mutations in either APC (FAP) or DNA mismatch repair genes (Lynch syndrome). (8,9) While the same screening methods are generally used for people at risk of these cancers, the recommendations are for more frequent and earlier screening, focusing particularly on methods which can image the entire colon (e.g. colonoscopy and double-contrast barium enema discussed below). (1) In addition to screening, there is also genetic testing that can be performed to identify at-risk individuals with a significant family history of colorectal cancer.
Colorectal-cancer screening methods
Colorectal adenomas have a high prevalence, occurring in >30% of people over age 60. (11) Of these, approximately 5% progress to cancer, so it is clinically important to be able to determine which adenomas might progress to cancer. Colorectal cancer develops from an early adenoma to a carcinoma over five to 12 years, and from a carcinoma to metastatic disease over two to three years. (12) This "window period" makes colorectal cancer amenable to screening. Current recommendations for screening are based on age and risk factors, such as a family history or personal history of colorectal cancer. The American Cancer Society currently recommends that beginning at age 50 (average risk), one of several screening protocols be followed (see Table 1). (13) For example, it is recommended that a yearly FOBT and a flexible sigmoidoscopy should be performed and repeated every five years. Alternatively, double-contrast barium enema or colonoscopy should be performed every five to 10 years. These screening tests are to be performed earlier and more often when the risk of colorectal cancer is elevated as outlined in Table 1.
Fecal occult blood testing
The most commonly used screening method for colorectal cancer is the fecal occult blood test (FOBT). In fact, a number of studies support that FOBTs reduce colorectal-cancer mortality rates by 15% to 20%. (14-16) FOBTs detect trace amounts of blood in the stool otherwise unapparent through simple inspection. The classical and inexpensive method of FOBT is a guaiac-based test, which takes advantage of the peroxidase-like activity of heme to screen for blood. Heme converts [alpha]-guaiaconic acid to a bright blue quinone compound in a rapid colorimetric reaction, corresponding to the amount of hemoglobin in the sample. The detection limits of FOBT vary between tests and manufacturers. For example, Beckman Coulter's Hemoccult II detects 0.2 mL blood per 100 g stool, Beckman Coulter's Hemoccult II Sensa test detects 0.3 mg/g stool, and Aerscher Diagnostics Hemaprompt test detects 2 mg/g stool. Although these tests are easy to use and inexpensive, they are sensitive to numerous dietary and therapeutic interferences including red meat, NSAIDS (nonsteroidal anti-inflammatory drugs), corticosteroids, anticoagulants, chemotherapeutic drugs, as well as high quantities of alcohol, ascorbic acid, citrus fruits and juices. (17) FOBTs are also prone to false positive results due to unrelated causes of gastrointestinal (GI) bleeding. As many as 50% of colorectal cancers and 80% of adenomas are not detected by classical FOBT screening methods. (18) This is likely caused by the fact that not all lesions bleed, and bleeding can occur intermittently. (19,20)
Immunochemical markers of colorectal cancer
Other markers are designed to detect proteins found in particular types of blood cells that are shed in feces. For example, neoplastic polyps are known to release tumor-associated leukocytes, which can be detected by assays for leukocyte-specific proteins, such as calprotectin. Calprotectin is a cytosolic protein found in neutrophils, which are shed through adenomas. Although it is not subject to the intermittent variation of FOBTs and preliminary studies promoted its use as a biomarker, calprotectin is neither sensitive nor specific enough to be considered a useful marker for colorectal cancer. (21)
Because of the limitations of markers for blood or blood cells in stool samples, there is considerable interest in developing screening tests based on neoplastic markers in colonocytes. Colonocytes are the cells that line the gastrointestinal epithelium and offer several advantages over FOBTs. For example, whereas FOBTs may yield false negatives due to the intermittent bleeding, colonocytes are regenerated and shed continuously in feces. (22) Colonocytes are also shed at a higher rate in the presence of colorectal cancer and are, therefore, more likely to be abundant in a positive sample.
Colonocyte tests also share the same advantage as FOBTs with respect to being non-invasive, relatively inexpensive, and relatively easy to perform. The best studied example of colonocyte testing in feces is the minichromosome maintenance proteins (MCM). MCM-2 is present in the nuclei of colonocytes and is essential for DNA replication. It is normally expressed in epithelium of the lower (distal) colon, but is expressed throughout the epithelium in the presence of colorectal cancer. MCM-2 can be detected by immunocytochemi-cal staining of fecal colonocytes, where positive cells correlate with disease. (23) Few clinical studies have been performed with MCM-2, but initial results demonstrate high sensitivity and specificity for colorectal cancer. Other protein markers in fecal colonocytes are currently being explored, such as carcinoembryonic antigen (CEA, discussed below). (24)
Imaging methods for colorectal-cancer screening
As a more sensitive and specific alternative to FOBTs, several imaging methods are used to detect gross abnormalities found in adenomas and colorectal cancer. The current gold standard for colorectal-cancer screening is colonoscopy, which involves direct visualization of the GI tract with a flexible fiber-optic camera. This method has several advantages over other imaging modalities including visualization of the entire GI tract and the opportunity to remove suspect polyps during the procedure. Colonoscopy has the highest specificity and sensitivity of currently available tests (see Table 2). (25,26) Although colonoscopy procedures are relatively invasive and expensive and include the risk of patient sedation and bowel perforation, it remains unsurpassed in diagnostic and therapeutic value. (27)
A slightly less invasive form of endoscopy is flexible sigmoidoscopy. Unlike colonoscopy, sigmoidoscopy does not require intravenous sedation (see Table 2). This method, however, only allows visualization of the distal portion of the colon and rectum. Sigmoidoscopy is reported to have a high sensitivity and specificity, and case-control studies indicate a 50% to 95% reduction in mortality in individuals screened with sigmoidoscopy. (28,29)
Double-contrast barium enema is another imaging technique that is used to visualize the GI tract. Double-contrast barium enema enables visualization of the entire colon after rectal administration of barium contrast dye and air. While this method is generally considered less sensitive at detecting early-stage polyps than either colonoscopy or sigmoidoscopy, (30) it is useful for symptomatic patients with advanced disease (see Table 2). A positive double-contrast barium enema requires a follow-up colonoscopy to remove abnormal polyps, which is an obvious drawback to the method.
Within the last decade, a less-invasive imaging approach has been developed termed "virtual colonoscopy." Virtual colonoscopy involves examination of a computer-generated 3D representation of the entire GI tract by reconstructing either computerized tomography (CT) or magnetic resonance (MR) imaging. This method detects lesions based on their size rather than histology. It is unable to distinguish a benign adenoma from an invasive carcinoma. Virtual colonoscopy, however, is more accepted by patients than colonoscopy, particularly in instances where patients have a high risk of complications or obstructing tumors are present (31). However, the availability of the method is currently limited and expensive and is not generally considered for general screening at this time (see Table 2). (25)
Check the DNA: molecular markers of colorectal cancer
The model of the genetic sequence for progression from adenoma to carcinoma has led to the development of a variety of DNA-based screening tests to directly detect DNA mutations from sloughed-off colonocytes. The majority of DNA tests detect either the loss of tumor-suppressor genes such as TP53 and APC, or the activation of oncogenes such as K-ras. Modern molecular techniques enable qualitative analysis of these mutations in a relatively minute amount of DNA retrieved from stool. Initially, methods employed PCR (polymerase chain reaction) on extracted DNA followed by automated sequencing. As this method was subject to insufficient recovery, newer assays have combined this approach with probe specific hybridization to capture and stabilize fragments of interest. (32)
Fecal DNA analysis represents a promising non-invasive approach to screen for mutations associated with colorectal cancer. Numerous studies identifying single mutations to diagnose colorectal cancer have variable reported sensitivities (see Table 3). For example, mutations in APC, which regulates genes involved in cell growth, are only detectable in ~60% of adenomas and colorectal cancers. Because APC mutations occur early on in the progression of colorectal cancer, APC has been proposed as a useful marker for detecting early lesions. (33) Mutations in K-ras, a small G-protein involved in differentiation and proliferation, has also been investigated as a marker of colorectal cancer as point mutations occur in 30% to 40% of colorectal carcinomas. (34) Other genes commonly mutated include the cell cycle regulatory gene TP53, and microsatellite instability (MSI) genes such as BAT26. MSI and TP53 mutations tend to occur late in tumorigenesis; MSI gene mutations allow damaged DNA to be replicated, and TP53 mutations result in unchecked growth. TP53 mutations are only found in 5% to 20% of early adenomas, but as much as 75% of colorectal cancer. (35) Limited sensitivity and specificity of these individual markers, as well as the relatively high cost of DNA analysis have made the detection of individual mutations less attractive (see Table 3). Moreover, positive results must still be followed up with colonoscopy.
In addition to specific DNA mutations, other more global molecular changes occur in malignant colonocytes. In healthy individuals, apoptotic cells are normally found in stool as part of the normal regeneration of the GI tract. In contrast, both adenomas and colorectal cancer shed non-apoptotic cells. Accordingly, intact, or "long DNA," found in non-apoptotic cells can be detected as a potential marker of neoplastic colonocytes. Clinical studies report that 56% of patients with colorectal cancer have the long DNA in comparison to only 3% of healthy people. (36) In addition to long DNA markers, other abnormalities can be found in colorectal cancers. DNA methylation is dysregulated during the progression from adenoma to carcinoma. Several studies investigating DNA hyper-methylation in colorectal cancer report sensitivities and specificities ranging from 50% to 70% and 70% to 90% respectively, for vimentin and SFRP2 (secreted frizzled-related protein 2). (37,38) While these methods are also considered too insensitive to use alone, they have been investigated for use in combination with other markers in "multi-target DNA assays." (39)
Multitarget DNA assays: a DNA bar code of colorectal cancer?
In an effort to increase the performance characteristics of individual DNA markers, multi-target assays designed to detect multiple mutations have been developed. In these assays, several different gene mutations are assessed simultaneously, yielding significant improvements in sensitivity and specificity for colorectal cancer (see Table 3). This improved performance stems from the fact that single gene mutations only occur in a small percentage of overall tumors (30% to 60%, depending on the marker; see Table 3). Recent studies of multi-DNA markers have sensitivities ranging from 65% to 100%, (40-42) which are significantly better than individual markers. However, more extensive clinical trials are required, and the costs of these assays are currently too high to be used as a screening procedure.
Serum markers of colorectal cancer
In addition to FOBTs, DNA markers, and imaging modalities, there are a number of serum proteins that have been studied as markers of colorectal cancer. These include carcinoembryonic antigen (CEA), and cancer antigens (CA) 19-9, 125, and 242. While serum markers are not sensitive enough for use in screening tests, they offer significant prognostic information and a way in which therapy may be monitored. (43,44) The most widely used serum marker is CEA, which is often elevated in colorectal cancers as well as other malignancies. It is currently recommended (by expert panels) that serum CEA concentrations be determined in newly diagnosed patients to aid in staging patients. (44,45) Drug-therapy efficacy can be monitored by CEA levels and used preoperatively as a baseline measure for patient management. CA 19-9 and other cancer antigens can also provide useful prognostic information, (46,47) but are still to be evaluated for routine use in monitoring colorectal cancer. APC has also been proposed as a serum marker of colorectal cancer, but sensitivity again remains a problem; a recent study reported ~60% detection rate for APC mutations in early, treatable carcinoma. (48) These methods may eventually be used in combination with other techniques as an effective colorectal cancer screen.
The future: proteomic approach to colorectal-cancer screening
The most recent development in determining screening biomarkers for colorectal cancer is a proteomic approach. Proteomics involves analysis of thousands of proteins found in either serum or tissue biopsies. While this approach not only identifies changes in protein concentrations over time, it can detect subtle epi-genetic changes, such as glycosylation or truncation, which are not detected by DNA screens. Proteomic studies of colorectal cancer were initiated to expand the knowledge base of the molecular pathology of the disease. To date, a handful of proteomic studies have compared protein expression profiles of thousands of proteins in healthy individuals to those from diseased patients. These methods typically rely on Surface Enhanced Laser Desorption Ionization Time-of-Flight (SELDI-TOF) or Matrix Assisted Laser Desorption Ionization Time-of-Flight (MALDI-TOF) mass spectrometry to identify differential expressed proteins separated by 2D electrophoresis. Electrophoresis is used to separate proteins based on charge and size, enabling visualization of spots corresponding to individual proteins; mass spectrometry can then be used to identify the proteins. Preliminary results suggest that proteomics can readily distinguish normal tissue from adenomas even at very early stages. (49) This method, however, has not been evaluated as a non-invasive screening tool and, therefore, this approach is considered investigational.
Current screening methods for colorectal cancer remain insufficient to lower mortality. This may be directly a result of the invasive nature of the colonoscopy and low patient compliance with recommended screening procedures. Newer methods, such as DNA markers, offer the potential for more rapid, less invasive screening but have not been integrated into screening methods to date. While multi-DNA panels appear promising, cost and availability are still problematic. In the future, novel proteomic methods may enable effective screening, but imaging techniques, such as colonoscopy, remain irreplaceable. Ultimately, it is likely that a combination of different methods will emerge, depending on risk stratification and technology prevalence.
Chris McCudden, PhD, works with the University of North Carolina Hospitals, McLendon Clinical Laboratories, in Chapel Hill, NC, and Monte S. Willis, MD, PhD, works with the Department of Pathology and Laboratory Medicine, University of North Carolina, also in Chapel Hill.
1. American Cancer Society. Cancer facts and figures 2006. Atlanta; American Cancer Society; 2006.
2. Levin B. Molecular screening testing for colorectal cancer. Clin Cancer Res. 2006;12:5014-5017.
3. Davies RJ, Miller R, Coleman N. Colorectal cancer screening: prospects for molecular stool analysis. Nat Rev Cancer. 2005;5:199-209.
4. Landis SH, Murray T, Bolden S, Wingo PA. Cancer statistics, 1998. CA Cancer J Clin. 1998;48:6-29.
5. O'Connell JB, Maggard MA, Ko CY. Colon cancer survival rates with the new American Joint Committee on Cancer sixth edition staging. Journal of the National Cancer Institute. 2004;96:1420-1425.
6. Fearon ER, Vogelstein B. A genetic model for colorectal tumorigenesis. Cell. 1990;61:759-767.
7. Hayne D, et al. Current trends in colorectal cancer: site, incidence, mortality and survival in England and Wales. Clin Onco(R Coll Radiol). 2001;13:448-452.
8. Balmana J, et al. Prediction of MLH1 and MSH2 mutations in Lynch syndrome. JAMA. 2006;296:1469-1478.
9. Hampel H, et al. Screening for Lynch syndrome (hereditary nonpolyposis colorectal cancer) among endometrial cancer patients. Cancer Res. 2006;66:7810-7817.
10. Burt R, Neklason DW. Genetic testing for inherited colon cancer. Gastroenterology. 2005;128:1696-1716.
11. Visser O. Incidence of Cancer in The Netherlands 1997. Ninth Report of the Netherlands Cancer Registry. Netherlands Cancer Registry. 2001.
12. Rhodes JM. Colorectal cancer screening in the UK: Joint Position Statement by the British Society of Gastroenterology, The Royal College of Physicians, and The Association of Coloproctology of Great Britain and Ireland. Gut. 2000;46:746-748.
13. American Cancer Society Guidelines for the Early Detection of Cancer. American Cancer Society. 2006.
14. Hardcastle JD, et al. Randomised controlled trial of faecal-occult-blood screening for colorectal cancer. Lancet. 1996;348:1472-1477.
15. Kronborg O, Fenger C, Olsen J, Jorgensen OD, Sondergaard O. Randomised study of screening for colorectal cancer with faecal-occult-blood test. Lancet. 1996;348:1467-1471.
16. Mandel JS, et al. Reducing mortality from colorectal cancer by screening for fecal occult blood. Minnesota Colon Cancer Control Study. N Engl J Med. 1993;328:1365-1371.
17. Henderson AR, Rinker AD. Gastric, Pancreatic, and Intestinal Function. In Burtis CA, Ashwood ER (eds): Tietz textbook of clinical chemistry, 3rd ed. W.B. Saunders, Philadelphia, 1999;1271-1327.
18. Ahlquist DA, McGill DB, Schwartz S, Taylor WF, Owen RA. Fecal blood levels in health and disease. A study using HemoQuant. N Engl J Med. 1985;312:1422-1428.
19. St John, DJ. Screening tests for colorectal neoplasia. J Gastroenterol Hepatol. 1991;6:538-544.
20. Young GP, St John DJ, Rose IS, Blake D. Haem in the gut. Part II. Faecal excretion of haem and haem-derived porphyrins and their detection. J Gastroenterol Hepatol. 1990;5:194-203.
21. Limburg PJ, et al. Prospective evaluation of fecal calprotectin as a screening biomarker for colorectal neoplasia. Am J Gastroenterol. 2003;98:2299-2305.
22. Ahlquist DA, Harrington JJ, Burgart LJ, Roche PC. Morphometric analysis of the "mucocellular layer" overlying colorectal cancer and normal mucosa: relevance to exfoliation and stool screening. Hum Pathol. 2000;31:51-57.
23. Gonzalez MA, Tachibana KE, Laskey RA, Coleman N. Control of DNA replication and its potential clinical exploitation. Nat Rev Cancer. 2005;5:135-141.
24. Kim Y, et al. Gastrointestinal tract cancer screening using fecal carcinoembryonic antigen. Ann Clin Lab Sci. 2003;33:32-38.
25. Cotton PB, et al. Computed tomographic colonography (virtual colonoscopy): a multicenter comparison with standard colonoscopy for detection of colorectal neoplasia. JAMA. 2004;291:1713-1719.
26. Rockey DC, et al. Analysis of air contrast barium enema, computed tomographic colonography, and colonoscopy: prospective comparison. The Lancet. 2005;365:305-311.
27. Winawer S, et al. Colorectal cancer screening and surveillance: clinical guidelines and rationale-Update based on new evidence. Gastroenterology. 2003;124:544-560.
28. Newcomb PA, Norfleet RG, Storer BE, Surawicz TS, Marcus PM. Screening sigmoidoscopy and colorectal cancer mortality. J Natl Cancer Inst. 1992;84:1572-1575.
29. Selby JV, Friedman GD, Quesenberry CP Jr. Case-control evaluation of screening. J Clin Epidemiol. 1996;49:390-391; author reply 391-392.
30. Luboldt W, et al. Computer-aided diagnosis in contrast-enhanced CT colonography: an approach based on contrast. Eur Radiol. 2002;12:2236-2241.
31. Fenlon HM, McAneny DB, Nunes DP, Clarke PD, Ferrucci JT. Occlusive colon carcinoma: virtual colonoscopy in the preoperative evaluation of the proximal colon. Radiology. 1999;210:423-428.
32. Whitney D, et al. Enhanced retrieval of DNA from human fecal samples results in improved performance of colorectal cancer screening test. J Mol Diagn. 2004;6:386-395.
33. Powell SM, et al. APC mutations occur early during colorectal tumorigenesis. Nature. 1992;359:235-237.
34. Forrester K, Almoguera C, Han K, Grizzle WE, Perucho M. Detection of high incidence of K-ras oncogenes during human colon tumorigenesis. Nature. 1987;327:298-303.
35. Vogelstein B, et al. Genetic alterations during colorectal-tumor development. N Engl J Med. 1988;319:525-532.
36. Boynton KA, Summerhayes IC, Ahlquist DA, Shuber AP. DNA integrity as a potential marker for stool-based detection of colorectal cancer. Clin Chem. 2003;49:1058-1065.
37. Chen WD, et al. Detection in fecal DNA of colon cancer-specific methylation of the nonexpressed vimentin gene. J Natl Cancer Inst97. 2005;1124-1132.
38. Muller HM, et al. Methylation changes in faecal DNA: a marker for colorectal cancer screening? Lancet. 2004;363:1283-1285.
39. Brenner DE, Rennert G. Fecal DNA biomarkers for the detection of colorectal neoplasia: attractive, but is it feasible? J Natl Cancer Inst. 2005;97:1107-1109.
40. Ahlquist DA, et al. Colorectal cancer screening by detection of altered human DNA in stool: feasibility of a multitarget assay panel. Gastroenterology. 2000;119:1219-1227.
41. Dong SM, et al. Detecting colorectal cancer in stool with the use of multiple genetic targets. J Natl Cancer Inst. 2001;93:858-865.
42. Tagore KS, Levin TR, Lawson MJ. The evolution to stool DNA testing for colorectal cancer. Aliment Pharmacol Ther. 2004;19:1225-1233.
43. Duffy MJ. Carcinoembryonic antigen as a marker for colorectal cancer: is it clinically useful? Clin Chem. 2001;47:624-630.
44. Duffy MJ, et al. Clinical utility of biochemical markers in colorectal cancer: European Group on Tumour Markers (EGTM) guidelines. Eur J Cancer. 2003;39:718-727.
45. Bast RC Jr, et al. 2000 update of recommendations for the use of tumor markers in breast and colorectal cancer: clinical practice guidelines of the American Society of Clinical Oncology. J Clin Oncol. 2001;19:1865-1878.
46. Carpelan-Holmstrom M, et al. CEA, CA 242, CA 19-9, CA 72-4 and hCGbeta in the diagnosis of recurrent colorectal cancer. Tumour Biol. 2004;25:228-234.
47. Louhimo J, Kokkola A, Alfthan H, Stenman UH, Haglund C. Preoperative hCGbeta and CA 72-4 are prognostic factors in gastric cancer. Int J Cancer. 2004;111:929-933.
48. Diehl F, et al. Detection and quantification of mutations in the plasma of patients with colorectal tumors. Proc Natl Acad Sci USA. 2005;102:16368-16373.
49. Polley AC, et al. Proteomic analysis reveals field-wide changes in protein expression in the morphologically normal mucosa of patients with colorectal neoplasia. Cancer Res. 2006;66:6553-6562.
50. Glick SN, et al. Comparison of Colonoscopy and Double-Contrast Barium Enema. 2000;343:1728-1730.
51. Winawer SJ, et al. A Comparison of Colonoscopy and Double-Contrast Barium Enema for Surveillance after Polypectomy. 2000;342:1766-1772.
52. Mak T, Lalloo F, Evans DG, Hill J. Molecular stool screening for colorectal cancer. Br J Surg. 2004;91:790-800.
53. Traverso G, et al. Detection of APC mutations in fecal DNA from patients with colorectal tumors. N Engl J Med. 2002;346:311-320.
54. Traverso G, et al. Detection of proximal colorectal cancers through analysis of faecal DNA. Lancet. 2002;359:403-404.
55. Eguchi T, Shirao K. [S-1 as a single agent for colorectal cancer]. Gan To Kagaku Ryoho. 2006;33(suppl 1):121-124.
56. Puig P, et al. A highly sensitive method for K-ras mutation detection is useful in diagnosis of gastrointestinal cancer. Int J Cancer. 2000;85:73-77.
57. Ratto C, et al. Detection of oncogene mutation from neoplastic colonic cells exfoliated in feces. Dis Colon Rectum. 1996;39:1238-1244.
58. Villa E. Molecular screening for colon cancer detection. Dig Liver Dis. 2000;32:173-177.
59. Tagore KS, et al. Sensitivity and specificity of a stool DNA multitarget assay panel for the detection of advanced colorectal neoplasia. Clin Colorectal Cancer. 2003;3:47-53.
By Christopher McCudden, PhD, and Monte S. Willis, MD, PhD
RELATED ARTICLE: The Colossal Colon
Molly McMasters, shown inside her brainchild--the Colossal Colon--works tirelessly to raise awareness about colon cancer. McMasters was diagnosed with stage II colon cancer at age 22 after six months of misdiagnoses. After her close friend, Amanda Sherwood Roberts, died at 27 from colorectal cancer, McMasters was inspired to create the Colossal Colon to "educate the public in memory of Amanda."
The Colossal Colon, affectionately referred to as "Coco," is a 40-foot long, four-foot tall model of the human colon that gives a unique perspective on colonic conditions such as Crohn's disease, diverticulosis, ulcerative colitis, hemorrhoids, cancerous and non-cancerous polyps, and progressive stages of colon cancer. Medical experts ensured that the replica was scientifically accurate. Coco has toured 74 cities in 34 states and Canada, appearing at hospitals, malls, convention centers, state fairs, museums, and at the Rockefeller Center Plaza on the "Today" show in 2002.
The Colossal Colon is just one aspect of advocacy efforts initiated by The Colon Club, a non-profit organization dedicated to raising awareness of colorectal cancer, also founded by McMasters along with Hannah Vogler, a cousin of Roberts. They and the Colon Club staff think up unusual ways to bring attention to colon cancer. Other exploits include a 2,000-mile trek on inline skates from New York to Colorado, dubbed "Rolling to Recovery," and the yearly publication of "The Colondar"--a delicately risque calendar featuring colon-cancer survivors.
McMasters also raises awareness by playing in the annual Cross-Checking Colon Cancer Women's Ice Hockey Tournament, in addition to being one of few females signed to play with the men's minor United Hockey League. Says McMasters, "Colorectal cancer can happen to anyone at any time, and I am determined to prove that to everyone who will listen." For more information about the organization or how to arrange a visit from Coco, go to www.thecolonclub.com.
CE test on DNA bar code: screening methods of colorectal cancer
MLO and Northern Illinois University (NIU), DeKalb, IL, are co-sponsors in offering continuing education units (CEUs) for this issue's article on DNA BAR CODE: SCREENING METHODS OF COLORECTAL CANCER. CEUs or contact hours are granted by the College of Health and Human Sciences at NIU, which has been approved as a provider of continuing education programs in the clinical laboratory sciences by the ASCLS P.A.C.E.[R] program (Provider No. 0001) and by the American Medical Technologists Institute for Education (Provider No. 121019; Registry No. 0061). Approval as a provider of continuing education programs has been granted by the state of Florida (Provider No. JP0000496), and for licensed clinical laboratory scientists and personnel in the state of California (Provider No. 351). Continuing education credits awarded for successful completion of this test are acceptable for the ASCP Board of Registry Continuing Competence Recognition Program. After reading the article on page 10, answer the following test questions and send your completed test form to NIU along with the nominal fee of $20. Readers who pass the test successfully (scoring 70% or higher) will receive a certificate for 1 contact hour of P.A.C.E.[R] credit. Participants should allow four to six weeks for receipt of certificates.
The fee for this continuing education test is $20.
All feature articles published in MLO are peer-reviewed.
Objectives and CE test questions prepared by Debbi Tiffany, MSEd, MT(ASCP)SC, SLS, CLS Program Director/POCT/QI/Safety, Swedish American Hospital, Rockford, IL.
1. In the developed world, the risk of developing colorectal cancer is approximately
2. All polyps are considered neoplastic.
3. This gene is among the first step mutations in the adenoma-carcinoma sequence model.
4. The majority of adenocarcinomas originate in the
b. proximal colon.
c. distal colon.
d. rectum and sigmoid colon.
5. The majority of colorectal cancers are hereditary.
6. What makes colorectal cancer amenable to screening tests?
a. Only about 5% of adenomas actually progress to cancer.
b. It takes approximately 5-12 years for adenomas to progress to carcinoma.
c. It takes approximately 2-3 years for carcinoma to develop into metastatic disease.
d. All of the above.
7. Which of the following people should have earlier or more frequent screening for colorectal cancer?
a. A patient with a history of chronic inflammatory bowel disease.
b. A 36 year old female whose parents both have a history of colon cancer.
c. A patient who has already had numerous adenomatous polyps.
d. All of the above.
8. Interference from guaiac based fecal occult blood tests may occur with
a. ingestion of red meat.
b. use of NSAIDS.
c. use of ascorbic acid.
d. ingestion of certain citrus fruits and juices.
e. all of the above.
9. Intermittent bleeding, or no bleeding at all can contribute to false negative fecal occult blood tests.
10. Calprotectin is a protein produced by
11. Colonocytes are shed at a lower rate in the presence of colorectal cancer.
12. The test with the highest specificity and sensitivity for colorectal cancer is the
a. double-contrast barium enema.
b. "virtual colonoscopy."
d. flexible sigmoidoscopy.
13. Flexible sigmoidoscopy enables visualization of the entire colon.
14. "Virtual colonoscopy" detects lesions based on
a. protein composition.
b. histological features.
c. immunochemical staining pattern.
15. The presence of apoptotic cells in stool is an abnormal finding.
16. Serum markers such as Carcinoembryonic antigen (CEA) are best used
a. as a screening test for colorectal cancer.
b. for prognosis in treating colorectal cancer.
c. to stage patients with colorectal cancer.
d. b and c.
17. DNA markers such as APC or K-ras are often considered too expensive or have limited sensitivity or specificity to be used individually in screening for colorectal cancer.
18. Proteomic studies examine
a. single proteins.
b. pairs of proteins.
c. only unchanged proteins.
d. thousands of proteins.
19. SELDI-TOF and MALDI-TOF are examples of
a. DNA barcoding.
b. serum markers of colorectal cancer.
c. methods utilized in proteomics.
20. Compliance with current colorectal screening procedures is fairly high.
Table 1. American Cancer Society colorectal-cancer screening recommendations Beginning at age 50, both men and women should follow one of these five testing schedules: * Annual fecal occult blood test (FOBT) (1) or fecal immunochemical test (FIT) * Flexible sigmoidoscopy every five (5) years * Annual FOBT (2) or FIT, and flexible sigmoidoscopy every five (5) years * Double-contrast barium enema every five (5) years * Colonoscopy every 10 years (1) Take-home multiple sample method is recommended. (2) All positive tests should be followed up with colonoscopy. Screening should be earlier and more often with colorectal cancer risk factors as follows: * Personal history of colorectal cancer or adenomatous polyps * Family history of colorectal cancer or polyps (cancer or polyps in a first-degree relative [parent, sibling, or child] younger than 60 or in two first-degree relatives of any age) * History of chronic inflammatory bowel disease * Family history of an hereditary colorectal cancer syndrome (familial adenomatous polyposis or hereditary non-polyposis colon cancer) Table 2. Existing and potential methods for colorectal-cancer screening Test Sensitivity* Specificity* Cost Imaging Techniques Flexible 97% (3) 94% (3) Moderate sigmoidoscopy Double-contrast Variable (50,51) Variable (50,51) High (51) barium enema Colonoscopy 97% (3) 98% (3) High Virtual 55% for > 1cm 100% for > 1cm Very high colonoscopy lesions (25) lesions (25) (CT or MRI) Stool Markers Fecal occult ~20 to 50% (3) ~20% (3) Low blood test (FOBT) Immunochemical 68% to 89% (52) 68% to 91% (52) Low to markers Calprotectin Calprotectin moderate 90% (52) 100% (52) MCM2 MCM2 Test Invasiveness Comments Imaging Techniques Flexible Invasive; requires Only effective for distal colon sigmoidoscopy bowel preparation Double-contrast Invasive; requires Low risk to patient, but barium enema bowel preparation sensitivity depends on endoscopist (50,51). Colonoscopy Significant Gold standard patient prep; sedation; risk of bowel perforation Virtual Minimal; some Currently investigational colonoscopy radiation exposure (CT or MRI) Stool Markers Fecal occult Non-invasive Interference prone; repeats blood test required; insensitive and (FOBT) nonspecific Immunochemical Non-invasive Variable performance markers depending on marker; not available currently. *Sensitivity and specificity for colorectal cancer Table 3. DNA marker for colorectal cancer Currently in research and development phase Moderate-high cost, non-invasive DNA Markers Sensitivity* Specificity* APC mutations 61% (53) 100% (54) TP53 mutations 28% (55) Low to moderate K-ras mutations 55 to 88% (56-58) 95 to 100% (56-58) BAT26 mutations 40 to 50% (54) Low to moderate (54) Long DNA 56% (36) 97% (36) Hypermethylated DNA 53 to 83% (37,38) 77 to 90% (37,38) Microsatellite 37% (54) 100% (54) Instability Currently in research and development phase Expensive, Non-invasive Multi-DNA markers Sensitivity* Specificity* APC, TP53, K-ras, 63% to 91% (40,42) 94 to 99% (40,42) BAT26 and Long DNA APC, TP53, K-ras, 63% (59) 96% (59) BAT26 and DNA integrity APC, TP53, K-ras, 90% (40) 93% (40) BAT26, Long DNA TP53, K-ras, BAT26 70% (41) N/A Currently in research and development phase Moderate-high cost, non-invasive DNA Markers Comments APC mutations Found in both colorectal cancer and adenomas TP53 mutations Found in colorectal cancer but not adenomas K-ras mutations Not specific to colorectal cancer; positive with pancreatic diseases BAT26 mutations Not specific to colorectal cancer; also positive with pancreatic diseases Long DNA Frequently used in multi-DNA markers Hypermethylated DNA Marker of early and late stage colorectal cancers Microsatellite Potential screen for hereditary colorectal cancer Instability Currently in research and development phase Expensive, Non-invasive Multi-DNA markers Comments APC, TP53, K-ras, Low sensitivity for adenomas BAT26 and Long DNA APC, TP53, K-ras, Low false positive rate BAT26 and DNA integrity APC, TP53, K-ras, Additional high sensitivity for adenomas BAT26, Long DNA TP53, K-ras, BAT26 *Sensitivity and Specificity for colorectal cancer
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|Author:||McCudden, Christopher; Willis, Monte S.|
|Publication:||Medical Laboratory Observer|
|Article Type:||Cover story|
|Date:||Nov 1, 2006|
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