Sensitivity of Hemoccult test for large bowel cancer in high-risk subjects

Hemoccult Sensitivity Estimate in a Screening Program for Colorectal Cancer in the Province of Florence

The sensitivity of Hemoccult testing (HO) in a population-based screening for colorectal cancer was evaluated. HO sensitivity estimates were calculated as the ratio of screen-detected HO-positives to total screen or interval-detected cancers. Sensitivity was estimated according to 1, 2, and 3-year rescreening intervals. Corresponding estimates are 69.4%, 61.8% and 57.7%, respectively. No significant correlation was observed between HO sensitivity and other variables, such as calendar period, tumor stage or site, or patient age or sex. HO sensitivity as estimated in the present experience is consistent with other reports of population-based screenings. Screening every year would achieve too limited an increase in sensitivity, compared to biennal screening, to be worth the difficulties of doubling organizational efforts and costs.

[Colorectal cancer: from diagnosis to screening]

Colorectal cancer fulfils the conditions required for mass screening. Data from controlled studies indicate that it is possible to reduce colorectal cancer mortality at a population level using faecal occult blood testing. Screenings rely on biennial testing in between 50 and 74average risk subjects. Compliance must be over 50%. Colorectal cancer mortality decrease in this case between 15 and 18% in the general population, 33 and 39% among participants to screening. The European Commission, on the basis of available data recommended to organise colorectal cancer screening in the European Union. Generalisation of screening has become a reality in France. Epidemiological studies allow us to define subjects at very high risk (genetic origin) and high risk for colorectal cancer. Colonoscopy screening is recommended in first degree relatives of patients with colorectal cancer or large adenoma diagnosed before 60years or with two affected first-degree relatives, in subjects with an extended inflammatory bowel disease, or with a personal history of large bowel cancer or large adenoma. Promising research strategies are arising: immunochemical tests in the short term, stool-based DNA tests in stools and proteome-based approach in the long term.

Epidemiology and screening of colorectal cancer

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

Cost-effectiveness analysis of strategies for colorectal cancer screening in Japan

To determine the cost-effectiveness of colorectal cancer screening strategies in Japan and to determine the influence of long-term compliance with screening programs on the selection of strategies, the natural history of a simulated cohort of 40-year-old Japanese of both genders was modeled with and without colorectal cancer screening until age 75 years. Survival, number of complications, and direct medical costs were compared among several combinations of screening examinations. In addition, the age of initiating screening was varied, as was the long-term compliance rate. Strategies using immunological fecal occult blood test were found to be the most cost-effective. Immunological fecal occult blood test followed by colonoscopy, if positive, would save 24.05 (5.88 discounted) days of life and cost 28,420 yen (US $210) per screened person, thus offering a cost-effectiveness ratio of 1.765 million yen (US $13,100) per year of life saved. If long-term compliance is 100%, initiating screening at age 40 years offers more years of life saved and a low incremental cost of screening. However, if more likely dropout rates are considered, initiation at age 40 years is dominated by later initiation of screening.

Effect of rehydration on guaiac-based faecal occult blood testing in colorectal cancer screening

Screening for colorectal cancer by means of unhydrated Hemoccult (HO) is in progress in the Province of Florence since 1982. In 1990 rehydrated HO was introduced in the town of Empoli. Five adjacent municipalities where screening had started in 1987 were selected for comparison. In both areas subjects aged 40-70 were invited by mail to undergo the screening protocol. HO-positive subjects were invited to undergo either pancolonoscopy or a combination of left colonoscopy and double contrast barium enema. HO-negative subjects were invited to repeat screening 2 years later. The positivity rate of HO was significantly higher (P < 0.001) for rehydrated (5%) as compared to unhydrated (3.1%) HO. The positive predictive values for cancer (unhydrated: 5.8%; rehydrated: 8.9%) and for adenomas (unhydrated: 26.7%; rehydrated: 25.5%) did not significantly differ. The detection rates of rehydrated HO were significantly higher as compared to unhydrated HO both for cancer (0.37% vs 0.15%; P < 0.05) and adenomas (1.06% vs 0.72%; P < 0.05%). In the present experience rehydration doesn't produce any decrease in the positive predictive value for cancer or adenomas and the increase in the positivity rate appears quite acceptable when considering the significant increase in the detection rates of cancer and adenomas. We conclude that rehydrated HO should be introduced as the standard test for screening in order to increase sensitivity for colorectal cancer and adenomas.

Guaiac and immunochemical tests for faecal occult blood in colorectal cancer screening

Seven hundred and eighty-six subjects spontaneously referring to our Center performed two guaiac (Rehydrated Hemoccult II (R.HO), and Hemoccult Sensa (HO S.)), and two immunochemical (OC Hemodia (Hdia) and Hemeselect (Hsel)) faecal occult blood tests on three consecutive faecal determinations. The positivity rates of 3 day R.HO, HO S., Hdia, and Hsel were 4.8%, 5.6%, 8.4% and 11.2% respectively. One hundred and thirty-five of the 150 subjects with at least one positive test completed the diagnostic work-up. Cancer was detected in three subjects and adenomas in 15. Three-day specificity estimates of R.HO, HO S., Hdia and Hsel in the overall series were 96.1%, 96.0%, 93.8% and 91.2% respectively, the differences between guaiac and immunochemical tests being significant. Corresponding values of specificity as determined on the first faecal sample only in the overall series were 98.1%, 98.3%, 96.1% and 94.9% respectively. No significant difference in specificity is evident when 3-day guaiac tests are compared to 1-day immunochemical ones. Three-day immunochemical testing is not recommended for screening purposes due to its very low specificity. Nevertheless, 1-day immunochemical testing is almost as specific as 3-day guaiac testing. A preliminary estimate of colonic neoplasms detection rates shows no difference as well. The benefit of 1-day testing on screening acceptability is evident, but the impact on sensitivity should be evaluated in a screening situation with a proper study design and a larger sample size.

Bile acids and the increased risk of colorectal tumours after truncal vagotomy

An association between colorectal cancer and previous peptic ulcer surgery is reported. In a prospective screening study, 100 asymptomatic patients (80 men and 20 women) who had undergone truncal vagotomy at least 10 years previously were investigated by barium enema, colonoscopy and gallbladder ultrasonography. Control data were obtained from forensic autopsy subjects. The incidence of neoplasms greater than or equal to 1.0 cm in the vagotomized group was 14 per cent (11 adenomas, 3 carcinomas) and 3 per cent in controls (P = 0.01). Duodenal bile obtained at endoscopy from 21 vagotomized patients with normal gallbladders and from 21 control patients undergoing endoscopy was analysed by high performance liquid chromatography. The mean percentage of cholic (CA), chenodeoxycholic (CDCA), deoxycholic (DCA) and lithocholic (LCA) acids in the bile of vagotomized patients was 32.3, 45.6, 20.7 and 1.4 per cent respectively compared with 45.3, 36.2, 17.9 and 0.7 per cent respectively in controls. The increased proportions of CDCA and LCA and decreased proportions of CA in the duodenal bile of vagotomized patients were significant (P less than 0.001; P = 0.02; P = 0.007). Abnormalities in bile acid metabolism may help to explain the increased risk of colorectal neoplasia 10 years after truncal vagotomy.

Industrial risk factors for colorectal cancer

Colorectal cancer is the second most common malignancy in the United States, and its incidence rates have sharply increased recently, especially in males. Industrial exposures, both occupational and environmental, are important colorectal cancer risk factors that are generally unrecognized by clinicians. Migration studies have documented that colorectal cancer is strongly associated with environmental risk factors. The causal role of occupational exposures is evidenced by a substantial literature associating specific work practices with increased colorectal cancer risks. Industrially related environmental exposures, including polluted drinking water and ionizing radiation, have also been associated with excess risks. Currently, there is a tendency to attribute colorectal cancer, largely or exclusively, to dietary and other lifestyle factors, thus neglecting these industrially related effects. Concerted efforts are needed to recognize the causal role of industrial risk factors and to encourage government and industry to reduce carcinogenic exposures. Furthermore, cost-effective screening programs for high-risk population groups are critically needed to further reduce deaths from colorectal cancer.

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.