Screening for colorectal cancer

Screening for a disease is an important concept in modern day preventive medicine. The aim is early disease detection and treatment of both asymptomatic individuals and those at risk of the disease, with the goal of better survival. The WHO published a set of essential criteria for screening in 1968 and colorectal cancer has been identified as a candidate disease. Three methods of screening are evaluated here: fecal occult blood test, flexible sigmoidoscopy and colonoscopy. Newer techniques are still being studied and preliminary results are encouraging. The incidence of colorectal cancer in Asia has been increasing in association with changes in lifestyle and therefore, designing efficient, acceptable screening programs for these populations is an important issue in the prevention of this common malignant disease.     

Screening for colorectal cancer

Although there are several methods available for colon cancer screening, none is optimal. This article reviews methods for screening, including fecal occult blood tests, flexible sigmoidoscopy, colonoscopy, CT colonography, capsule endoscopy, and double contrast barium enema. A simple, inexpensive, noninvasive, and relatively sensitive screening test is needed to identify people at risk for developing advanced adenomas or colorectal cancer who would benefit from colonoscopy. It is hoped that new markers will be identified that perform better. Until then we fortunately have a variety of screening strategies that do work.     

Screening for colorectal cancer

PURPOSE: Screening for colorectal cancer using a guaiac-based fecal occult blood, or Hemoccult®, test has been demonstrated to reduce colorectal cancer mortality. However, the magnitude of effectiveness is relatively low because of poor sensitivity of the Hemoccult® test. The immunochemical fecal occult blood test has been shown to be much more sensitive than the Hemoccult® test in detecting preclinical colorectal cancer in an asymptomatic population. The purpose of this article is to discuss the validity of the immunochemical fecal occult blood test and the efficacy of a population-based screening program using the test. METHODS: Relevant articles were primarily identified through MEDLINE search. Review was focused on the studies of population screening programs with the immunochemical fecal occult blood test. RESULTS: Sensitivities for colorectal cancer calculated in the same population were reported to be 67 to 89 percent and only 33 to 37 percent for the immunochemical test and Hemoccult® test, respectively. Case-control studies and other observational studies showed that screening programs using the immunochemical fecal occult blood test by hemagglutination reaction would reduce the risk of dying of colorectal cancer by 60 percent or more for those screened annually compared with those unscreened. It was also shown that a screening strategy using the immunochemical fecal occult blood test had the best cost-effectiveness ratio among the methods available. Nearly 5 million persons are currently screened per year in Japan, yielding 0.15 to 0.2 percent colorectal cancer cases among persons with positive fecal occult blood test results. CONCLUSIONS: These results strongly suggest that a screening program with immunochemical fecal occult blood test has promising advantages in terms of effectiveness over programs with the Hemocult® test. More stress is warranted on introduction of immunochemical fecal occult blood testing as a screening test in place of the guaiac fecal occult blood test.     

Screening for colorectal cancer in Europe

The aim of the present study was to compare computer-based and visual/manual scoring of pressure recordings from the gastric antrum and duodenum. The computer system was based on three separate principles of recognition: moving average, tracking base line, and threshold filters. Computer scoring resulted in the detection of more contractions than visual/manual scoring, owing to inclusion of artefacts of duration and amplitude above the selected thresholds. Owing to its unreliability, visual/manual scoring led to inclusion of some contractions of below-borderline amplitude or duration. The median difference in the frequency of contractions was, however, Omin^?1. There was close agreement on amplitudes of contractions. As the differences between visual/manual analysis and computer-aided scoring by the present system are of an unimportant magnitude and as computer-based scoring is consistent, we conclude that computer-aided analysis is preferable to visual/manual analysis.     

Screening and surveillance for colorectal cancer

Pathologic reviews and clinical studies demonstrate that groups with increased cancer risk can be identified. It is estimated that about 3.5 per cent of colorectal cancers in this country are the result of known heritable cancer syndromes, such as familial polyposis. Much effort is currently being devoted to evaluation of biologic markers, such as cell surface antigens and their antibodies, ornithine decarboxylase, errors in DNA repair, abnormalities in metabolism of polyadenosine diphosphate, and application of molecular genetic techniques to identify patients with genetic cancer susceptibility.     

Screening of colorectal cancer

Colorectal cancer (CRC) remains a cancer in a disappointing location. However, its location clearly has an advantage that could theoretically permit efficient secondary prevention: the preceding of the cancer by a benign lesion, ie, the adenoma. Complete colonoscopy and its substitute, the double-contrast barium enema, and their specific limitations, must be reserved for high-risk patients: hereditary cancers and ulcerative colitis. For all the others, ie, adults of 45 years of age and with standard risks, the proposal is either to select the patients to be colonoscoped through occult blood testing of the stools or to perform a fibersigmoidoscopy or a combination of both. Although imperfect, both methods allow the detection of polyps and cancers at a presymptomatic stage, when they are either benign or malignant, but localized and with a better prognosis. However, the absolute proof of the benefits of this strategy of screening would be the demonstration by controlled studies of a prolonged survival rate or a decrease in morbidity. Until now, this proof is not fully available.     

Screening for colorectal cancer in the UK

Colorectal cancer fulfils the World Health Organisation criteria for disease screening. It is now well established that screening for colorectal cancer is effective in reducing both incidence as well as mortality. Various modalities of screening methods with inherent strengths and weaknesses are available. Due to the emergence of innovative new techniques, the best way ahead is debatable. Evidence indicates that faecal occult blood testing and 'once only' flexible sigmoidoscopy appears to be the most suitable mode of mass screening for the UK population.     

Screening for colorectal cancer in average-risk populations

Screening average-risk populations for colorectal cancer can reduce the incidence and mortality of colorectal cancer. Effectiveness depends on programmatic adherence and quality. This review discusses the evidence supporting the use of currently available screening tests. The discussion specifically focuses on programmatic issues and highlights the importance of quality assurance in each program.     

Screening an asymptomatic population for colorectal cancer

The best prospect of realizing a reduction in mortality from colorectal cancer appears to be by presymptomatic detection in a screened population. Presently, the only feasible method of mass population screening is by the detection of faecal occult blood and it is encouraging that all the major trials demonstrate that asymptomatic malignancy may be detected in this way. Furthermore, the screen-detected cancers are generally at an earlier pathological stage than those appearing in control populations. However, a note of caution is required. At the present time it is too early to demonstrate a reduction in mortality from the disease and there is evidence of a length bias, with more of the screen-detected cancers being well differentiated. The results of the large controlled trials will enable the benefits of screening to be viewed objectively and a recommendation for, or against, screening to be made.