Screening of colorectal tumours using an improved faecal occult blood test. Quantitative aspects

Screening for colorectal cancer by immunochemical fecal occult blood testing

Screening for colorectal cancer using the conventional Hemoccult test has been shown to reduce mortality associated with cancer by 33% through a randomized controlled trial. However, the magnitude of effectiveness is small in terms of cost-effectiveness. The recently developed immunochemical fecal occult blood test (IFOBT) provides a potential replacement for the Hemoccult test as a screening test, due to its superior performance characteristics such as higher sensitivity shown in preliminary studies and the fact that it does not require any dietary restriction. The IFOBT method is reviewed, especially in relation to its specificity. In known colorectal cancer subjects, IFOBTs have shown both higher sensitivity and specificity than the Hemoccult test. Similarly, IFOBT has demonstrated a higher sensitivity than Hemoccult for colorectal cancer in an asymptomatic population. A nationwide screening program in Japan has demonstrated the feasibility of this approach for large population screening. However, the positivity rate varied according to the conditions at each screening facility. Therefore, technical factors that influence the positivity rate of IFOBTs in the screening program are discussed. Case-control studies have strongly suggested that screening using IFOBT would reduce mortality from colorectal cancer by 60% or more. Several observational studies have provided support for this estimate. The feasibility and effectiveness of population-based screening by IFOBT are discussed.

Interval cancers in screening with fecal occult blood test for colorectal cancer

Interval cancers, which are cancers diagnosed in spite of one or more negative screening tests, were studied in a randomized population with Hemoccult-II for colorectal cancer in 61,938 persons between 45 and 74 years old. Three biannual screenings were performed from 1985 to 1991, and 52% of all the cancers detected after doing at least one Hemoccult-II test were interval cancers (81 persons). These were more advanced than cancers diagnosed after a positive Hemoccult-II test, of larger size, less frequently of Dukes stage A, more often invading neighboring organs, and less often resectable for cure. They were located in the rectum more often than cancers diagnosed by screening and cancers in controls. Otherwise, interval cancers did not differ from cancers in controls or cancers in non-responders, and all characteristics suggested that no delay in diagnosis resulted from one or more negative Hemoccult-II tests, compared with controls. However, even if screening with Hemoccult-II demonstrates a reduction in mortality from colorectal cancer, the present high number of interval cancers makes it necessary to look for other methods of screening populations for colorectal cancer.

Screening guidelines for colorectal cancer

A review is given of methods and results of screening for colorectal cancer in average-risk and high-risk groups. Possible methods are digital rectal exploration, endoscopic examination, barium enemas, faecal occult blood tests, tumour markers like carcinoembryonic antigen, Ca-19-9, and others, and gene markers. Final results of large randomized population studies with faecal occult blood tests are expected within the next few years, but it will probably be necessary to add flexible sigmoidoscopy to achieve a major reduction in mortality from colorectal cancer in average-risk persons. Recommendations for screening in high-risk groups are proposed, but strong support for these guidelines are still missing, an exception being first-degree relatives of individuals with familial adenomatous polyposis; the other high-risk groups include members of hereditary non-polyposis colorectal cancer families, relatives of patients with sporadic colorectal cancer, patients with colorectal adenomas, patients with previous colorectal cancer, and patients with inflammatory bowel disease.

Population screening for colorectal cancer, the goals and means

The causes of colorectal cancer are complex and in most cases obscure, making primary prevention impossible at present. Secondary prevention by finding and treating early asymptomatic cancers may possibly reduce mortality from this very common cancer. Results from conventional treatment have changed little during recent decades and are unsatisfactory, with more than half of the patients dying from the disease. The incidence has increased during recent years in many countries, making it vital to evaluate possible benefits from screening. This review considers different methods of screening for colorectal cancer and includes an overview of continuing European controlled randomised trials with the faecal occult blood test, Haemoccult-II. No final evaluation is possible, but advantages and drawbacks of different strategies are discussed. Assuming that the goal of reducing mortality is achieved, several other problems remain unsolved: the organisation of screening, the training of doctors in endoscopy, cost benefit and cost effectiveness all of which will have to be solved before a population screening can be recommended. Present screening tools are not ideal and we have to continue the search for better markers of early colorectal cancers and even possible precursors like adenomas.

Colonoscopic diagnosis and treatment of lower gastrointestinal bleeding

Methods of diagnosis and treatment of lower gastrointestinal bleeding depend on the rate of bleeding and the amount of blood lost. If bleeding is occult, colonoscopy is the single best way to determine the source, if bleeding is gross but mild, causing melena or small amounts of hematochezia, colonoscopy or a combination of flexible sigmoidoscopy and double-contrast barium enema should be used to evaluate the colon. In most patients with melena, the upper tract must be examined endoscopically. Acute lower gastrointestinal bleeding stops spontaneously in 75 to 90 per cent of patients, permitting preparation of the colon before colonoscopy. If bleeding is continuing, diagnostic options include colonoscopy with no preparation of the colon, relying on the cathartic effect of blood, or a red cell radionuclide scan followed by angiography if the scan is positive. A bleeding lesion seen on angiography is usually treated by infusion of vasopressin. Colonoscopic treatment of a bleeding site uses the BICAP probe, heater probe, or argon laser. Patients who bleed severely and those who do not respond to treatment or rebleed after treatment are candidates for operation. Segmental resection is preferred if the bleeding site is known. If not, total colectomy with ileorectal anastomosis may be necessary. A mortality rate of 10 to 15 per cent in patients with severe bleeding reflects the advanced age of many of these patients and the difficulty of managing gastrointestinal bleeding in the presence of associated medical conditions.