Switching from guaiac to immunochemical faecal occult blood test increases participation and diagnostic yield of colorectal cancer screening

BackgroundCompared with the guaiac-faecal occult blood test (gFOBT), faecal immunological tests (FIT) are considered to be more effective for colorectal cancer (CRC) screening. However, only scarce research has examined the outcomes of switching to FIT within a mature gFOBT-based CRC screening programme.MethodsWe reported a 15-year experience of biennial FOBT screening in a well-defined population of approximately one million inhabitants, including six gFOBT-based screening rounds and one round with FIT at the 30 μg Hb/g cut-off. The main outcome measures were screening participation, FOBT positivity and advanced neoplasia detection in each round.ResultsIn this study, 647 676 screenings were performed in 228 716 different individuals, leading to 17 819 positives and 16 580 follow-up colonoscopies. Compared with the last gFOBT round, switching to FIT led to an increased participation of nearly 20% points, and a fivefold increased detection of CRC and advanced adenoma among invitees (3-fold among attendees). The numbers needed to screen and scope to detect one advanced neoplasia declined from 221 to 66 and from 4.7 to 2.6, respectively.ConclusionsThe present population-based study demonstrated a dramatical increase in the diagnostic yield of advanced neoplasia by switching to FIT within a mature gFOBT-based CRC screening programme.     

Randomized study of biennial screening with a faecal occult blood test: results after nine screening rounds

BACKGROUND: Two large true population studies in Europe have shown a significant reduction in mortality from colorectal cancer (CRC) by screening with a faecal occult blood test. In one trial conducted in Funen County, 61,933 individuals (aged 45-75 years) were randomly allocated either to a control group or to receive a biennial Hemoccult-II test. METHODS: These individuals were followed from 1985 to 2002 and 9 screening rounds were performed. RESULTS: First screening was accepted by 67% (20,672). Positivity rates varied between 0.8% and 3.8%, and the cumulative proportion of the test group having colonoscopy was 5.3%. Screen-detected CRC was early (Dukes' A) in 36% compared to 11% among controls. Incidence of CRC was unchanged, but mortality was reduced by 11%. This figure increased to 43% in persons participating in all 9 rounds. No more than 8,558 were screened at the 9th round. Patients with CRC detected between screenings had better survival than controls. Death rates from causes other than CRC among participants never became higher than among controls. CONCLUSION: The lesser reduction in mortality from CRC of 11% compared to 18% after 5 screening rounds may be explained by the decrease in the number screened. Efficacy in those screened supports the introduction of countrywide screening in Denmark, but it must be ascertained that acceptability, proportion of early CRC and logistics all reach the same standard as in the randomized trial.     

The risks of screening: data from the Nottingham randomised controlled trial of faecal occult blood screening for colorectal cancer

AIMS: To determine the harm that ensues from faecal occult blood (FOB) screening for colorectal cancer. METHODS: 150 251 people were randomly allocated either to receive biennial Haemoccult FOB tests (n =75 253) or not to be contacted (n=74 998). Study group patients returning positive tests were offered colonic investigation; 1774 underwent complete investigation of the colon. RESULTS: There was no significant difference in the stage at presentation of interval versus control group cancers. Survival in the interval cancer group was significantly prolonged compared with the control group. Sensitivity for colonoscopy or flexible sigmoidoscopy and double contrast barium enema (DCBE) was 96.7%. There were no complications of DCBE but seven (0.5%) complications of colonoscopy, of which six required surgical intervention. There were no colonoscopy related deaths. No patients without colorectal cancer died within 30 days of colonic investigation. Five patients died within 30 days of surgery for screen detected colorectal neoplasia and a further two died without having surgery. Six patients died after 30 days but within two years of surgery for screen detected benign adenomas or stage A cancers; in all cases the cause of death was not related to colorectal cancer. CONCLUSIONS: There was investigation related morbidity but no mortality and little to support overdiagnosis bias. The group returning falsely negative tests had a better outcome compared with the whole control group. There is a negative side to any screening programme but mortality reduction in this and other trials suggests that a national programme of colorectal cancer screening should be given consideration.     

CT colonography after incomplete colonoscopy in subjects with positive faecal occult blood test

AIM： To report our experience with computed tomography colonography （CTC） systematically performed in subjects with positive faecal occult blood test （FOBT） and an incomplete colonoscopy in the setting of a population-based screening for colorectal cancer （CRC）.
METHODS： From April 2006 to April 2007, 43 290 individuals （age range 50-70） who adhered to the regional screening program for the prevention of CRC underwent immunochemical FOBT. FOBT was positive in 1882 subjects （4.3%）. 1463 （77.7%） of these subjects underwent colonoscopy, 903 performed in a single center. Of 903 colonoscopies 65 （7.2%） were incomplete. Forty-two of these subjects underwent CTC. CTC was performed with a 16-MDCT scanner after standard bowel prep （polyethyleneglycole） in both supine and prone position. Subjects whose CTC showed polyps or masses were referred to the endoscopist for repeat colonoscopy under sedation or underwent surgery. Perlesion and per-segment positive predictive values （PPV） were calculated.
RESULTS： Twenty-one （50%） of 42 CTCs showed polyps or masses. Fifty-five of these subjects underwent a repeat colonoscopy, whereas 2 subjects underwent surgery for colonic masses of indeterminate nature. Four subjects refused further examinations. CTC correctly identified 2 colonic masses and 20 polyps. PPV for masses or polyps greater than 9 mm was of 87.5%. Per-lesion and per-segment PPV were, respectively, 83.3% and 83.3% for polyps greater or equal to 10 mm, and 77.8% and 85.7% for polyps of 6-9 mm.
CONCLUSION： In the context of a screening program for CRC based on FOBT, CTC shows high per-segment and per-lesion PPV for colonic masses and polyps greater than 9 mm. Therefore, CTC has the potential to become a useful technique for evaluation of the non visualized part of the colon after incomplete colonoscopy.     

Short term outcomes of the first round of a pilot colorectal cancer screening programme with guaiac based faecal occult blood test

Objective

To assess both feasibility and short term outcomes of a population based colorectal cancer screening programme using a biennial guaiac based faecal occult blood test (gFOBT).

Method

All participants were invited by mail to take part in a screening programme using a non‐rehydrated gFOBT. The gFOBTs were first provided by general practitioners (GPs) and then directly mailed to individuals who failed to comply after two invitations. The setting was a French administrative district: Haut‐Rhin (710 000 inhabitants). 182 981 residents aged 50–74 years were invited to participate.

Results

19 274 people (10.5%) were excluded from gFOBT screening and 90 706 completed a gFOBT, so that the participation rate was 55.4% of those eligible. 76.5% of the completed gFOBTs were provided by GPs and 15.5% by direct mailing. The gFOBT positivity rate was 3.4%. The positive predictive value was 42.7% for neoplasia (women 30.8%, men 52.5%), 23.6% for advanced adenoma, and 7.6% for cancer. The number of normal colonoscopic procedures (without neoplasia) needed to be performed for each colonoscopy detecting an advanced neoplasia was 1.8, lower in men (1.2) than in women (3.4), and decreasing with age. Detection rates for neoplasia and cancer were 12.8 and 2.3 per 1000 people screened. 206 adenocarcinomas were detected: 47.6% were stage I and 23.8% stage II. The direct cost was estimated at €29.3 per screened person and €13 466 per cancer detected.

Conclusions

Participation and diagnostic yield of controlled trials of gFOBT screening are reproducible in the real world at an acceptable cost through an organised population based programme involving GPs.     

Fecal occult blood test in colorectal cancer screening

Colorectal cancer (CRC) is one of the leading causes of cancer‐related mortality worldwide. Cancer screening is known to decrease mortality from CRC. One important test for CRC screening is the fecal occult blood test (FOBT), which includes guaiac FOBT and fecal immunological tests. In this review we discussed the development and application of the FOBT in CRC screening.     

Faecal calprotectin and faecal occult blood tests in the diagnosis of colorectal carcinoma and adenoma

BACKGROUND AND AIMS: Testing for faecal occult blood has become an accepted technique of non-invasive screening for colorectal neoplasia but lack of sensitivity remains a problem. The aim of this study was to compare the sensitivity and specificity of faecal calprotectin and faecal occult blood in patients with colorectal cancer and colonic polyps. METHODS: Faecal calprotectin and occult blood were assessed in 62 patients with colorectal carcinoma and 233 patients referred for colonoscopy. The range of normality for faecal calprotectin (0.5-10.5 mg/l) was determined from 96 healthy subjects. RESULTS: Median faecal calprotectin concentration in the 62 patients with colorectal carcinoma (101 mg/l, 95% confidence interval (CI) 57-133) differed significantly from normal (2.3 mg/l, 95% CI 1.6-5.0) with 90% of patients having elevated levels (normal <10 mg/l) whereas only 36/62 (58%) had positive faecal occult bloods. There was no significant difference in faecal calprotectin levels when considering location or Dukes' staging of tumour. Percentage positivity of faecal occult bloods was significantly higher for Dukes' stage C and D cancers compared with Dukes' A and B. In the colonoscopy group, 29 patients with adenomatous polyps were detected in whom the median faecal calprotectin was 12 mg/l (95% CI 2.9-32). Sensitivity for detection of adenomatous polyps was 55% using the calprotectin method and 10% using faecal occult blood testing. The overall sensitivity and specificity of calprotectin for colorectal cancer and adenomatous polyps as a combined group was 79% and 72%, respectively, compared with a sensitivity and specificity of faecal occult blood of 43% and 92%. CONCLUSIONS: Faecal calprotectin is a simple and sensitive non-invasive marker of colorectal cancer and adenomatous polyps. It is more sensitive than faecal occult blood tests for detection of colorectal neoplasia at the cost of a somewhat lower specificity.     

Screening for colorectal cancer with immunochemical faecal occult blood tests

Population-based studies have shown that guaiac faecal occult blood testing followed by colonoscopy in case of positivity can reduce colorectal cancer mortality. However these tests have been criticised for their fairly low sensitivity. For this reason attention has been given to alternative tests. The aim of this paper is to review the evidence for screening for colorectal cancer using qualitative immunochemical faecal occult blood tests. For the complete range of tested cut-off values, immunochemical faecal occult blood tests lead to higher diagnostic yield, improved sensitivity and greater participation. The optimal number of samples and the optimal cut-off value has to suit local resources and the acceptability of missed cancers. All economic evaluations, despite some differences between studies, add further arguments to support the opinion that the immunochemical faecal occult blood test is currently the most cost-effective screening test for average-risk populations. These economic evaluations provide strong arguments in favour of the 1-sample strategy. With decreasing the cut-off value similar performances can be achieved with one-compared to two day sampling. Too few data are currently available to accurately compare existing qualitative tests.     

Comparison of immunochemical and guaiac-based fecal occult blood test in screening and surveillance for advanced colorectal neoplasms: A meta-analysis

OBJECTIVE: To systematically evaluate whether immunochemical fecal occult blood tests (iFOBT) could improve clinical performance and test accuracy in screening and surveillance for advanced colorectal neoplasms. METHODS: Eligible articles were identified by searches of electronic databases. All randomized trials and diagnostic cohort trials directly comparing iFOBT with guaiac-based FOBT (gFOBT) were included. A statistical analysis was performed using RevMan 4.2.8. A sensitivity, specificity and summary receiver operating characteristic curve was performed using Meta Disc. RESULTS: We identified five randomized trials and 11 diagnostic cohort trials. In the randomized trials, the detection rates of advanced colorectal neoplasms with iFOBT or gFOBT were 2.23 percent and 1.24 percent, respectively. The pooled odds ratio (OR) was 1.50 (95% CI 0.94–2.39). In cohort trials, the advanced neoplasm detection rates of iFOBT or gFOBT were 1.44 percent and 0.50 percent (OR 1.99, 95% CI 1.24–3.19) in the average-risk screened population, and were 8.8 percent and 7.1 percent (OR 1.27, 95% CI 1.01–1.60) in diagnosed patients scheduled for colonoscopy. The sensitivity of iFOBT (0.67, 95% CI 0.61–0.73) was superior to that of gFOBT (0.54, 95% CI 0.48–0.60), as well as the specificities (0.85, 95% CI 0.83–0.87 vs 0.80, 95% CI 0.78–0.82) and positive predictive values (0.41 vs 0.29) in cohort trials of diagnosed patients. CONCLUSION: Our review suggests that iFOBT could perform better in increasing the detection rate of advanced colorectal neoplasm than gFOBT and possesses higher sensitivity and specificity in the surveillance of advanced colorectal neoplasm for patients.     

Adherence to follow-up after a positive fecal occult blood test in an organized colorectal cancer screening program in Korea, 2004-2008

Background and Aim: To investigate the participation rates, positivity rates, and follow‐up rates from 2004 to 2008 in an organized colorectal cancer (CRC) screening program using a fecal occult blood test (FOBT) in Korea. Methods: The study population was men and women aged 50 years or older who were invited to participate in the National Cancer Screening Program for CRC between 1 January 2004 and 31 December 2008. We collected the FOBT results and follow‐up information for the FOBT positives. Results: Participation rates increased steadily each year from 10.5% in 2004 to 21.1% in 2008. Between 2004 and 2008, FOBT positivity rates declined from 8.0% to 6.8%. Among the FOBT‐positives, 61.3% of participants underwent either colonoscopy or double contrast barium enema (DCBE) in 2004, and this rate decreased to 38.6% in 2008. Age, health insurance type, and screening history were associated with adherence to follow‐up test after a positive FOBT. With regard to follow‐up tests, colonoscopy rates increased from 17.9% in 2004 to 27.6% in 2008, while DCBE decreased from 43.4% in 2004 to 11.0% in 2008. Colonoscopy was significantly more likely to be chosen as a follow‐up test by men, participants aged 50–59 years, and National Health Insurance beneficiaries. Conclusion: These findings suggest that targeting participants for follow‐up, based on age and previous screening history, could be a good way to improve the follow‐up rate.     

Relationship between the number of positive fecal occult blood tests and the diagnostic yield of colonoscopy

BACKGROUND:

In 2007, Ontario launched a colon cancer screening program for average-risk individuals based on biennial fecal occult blood tests (FOBTs) on three fecal samples, followed by colonoscopy for individuals who tested positive.

OBJECTIVE:

To determine whether >1 positive screening FOBT was predictive of finding advanced neoplasia at colonoscopy.

METHODS:

A retrospective chart review of outpatient colonoscopic procedures performed at Hotel Dieu Hospital (Kingston, Ontario) in the first two years of the colon cancer screening program was conducted, focusing on endoscopic and pathological findings.

RESULTS:

Of 5556 individuals undergoing colonoscopy, 346 were referred for positive FOBT. Overall, 41 (11.8%) patients with a positive FOBT had colon cancer. In 16 (4.6%) cases, the number of positive FOBTs was not reported. For the 330 individuals in whom the number of positive tests was specified, 198, 71 and 61 cases had one, two and three positive results, respectively. Cancer was found at colonoscopy in 11 (5.6%), 11 (15.5%) and 18 (29.5%) of individuals with one, two and three positive FOBT results, respectively (OR 3.0 [95% CI 1.2 to 7.3] and 6.5 [95% CI 2.8 to 15.0] for two or three positive FOBTs compared with one; P=0.015 and P<0.001, respectively). High-risk adenomas (>1 cm in diameter, villous component and/or high-grade dysplasia) were found in 41 (20.8%), 29 (42.0%) and 25 (41.0%) individuals with one, two and three positive FOBTs, respectively (OR 2.8 [95% CI 1.5 to 5.0] and 2.4 [95% CI 1.3 to 4.5] for two or three positive FOBTs compared with one; P=0.001 and P=0.006, respectively).

CONCLUSIONS:

The diagnostic yield of colonoscopy varied directly with the number of positive FOBTs. This information may be useful in assigning scheduling priority for patients with positive FOBTs.     

Colorectal cancer screening

Colorectal cancer is one of the most common malignancies in Australia, and screening to detect it an earlier stage is cost‐effective. Furthermore, detection and removal of precursor polyps can reduce incidence. Currently, there are limited data to determine the screening rate in Australia, but it is certainly lower than the 80% screening rate considered desirable. Whether colonoscopy is used as the screening test or to follow up positive results of an initial non‐invasive test, it plays a fundamental role. Despite high sensitivity and specificity, it is expensive and invasive with measurable risk and is not acceptable as an initial test to many participants. It does not provide complete protection, and interval cancers between planned colonoscopies are associated with proximal location, origin in sessile serrated adenomas and operator‐dependent factors. An essential component of colorectal screening is the measurement of colonoscopy quality indicators, such as caecal intubation and adenoma detection rates, which are known to be associated with the rate of interval cancer. The non‐invasive screening test currently recommended in Australia is biennial testing for faecal occult blood between the ages of 50 and 75 using a faecal immunochemical test, with positives evaluated by colonoscopy. This is provided through the National Bowel Cancer Screening Programme, currently for those at the ages of 50, 55, 60 and 65 years, with full implementation of biennial screening by 2020. To improve screening in Australia, the most fruitful approach may be to acknowledge that there is a choice of screening tests and to focus on the goal of improving overall participation rate and being able to measure this.     

Gastric cancer after positive screening faecal occult blood testing and negative assessment

BACKGROUND: Gastric cancer may be suspected with otherwise unexplained positive faecal occult blood testing. AIMS: To assess the frequency of gastric cancer following positive faecal occult blood testing and negative colonoscopy. SUBJECTS: Age 40-74 cohort at first screening (1985-2001) with (a) faecal occult blood testing- (83,489), (b) faecal occult blood testing +/colonoscopy+ (2025), or faecal occult blood testing+/colonoscopy- (3555). METHODS: Gastric cancer incidence in faecal occult blood testing subsets, compared with expected standardized incidence rates. RESULTS: Gastric cancer risk was increased (standardized incidence rate=146.7; 95% confidence interval: 105.8-203.4) in faecal occult blood testing+/colonoscopy- subjects. A four-fold excess incidence occurred during first year (observed cases=10, standardized incidence rate=408.3; 95% confidence interval: 219.7-758.8), irrespective of faecal occult blood testing type (guaiac, immunological). No excess risk occurred in faecal occult blood testing- (observed cases=53, standardized incidence rate=91.2; 95% confidence interval: 84.1-98.8) or in faecal occult blood testing+/colonoscopy+ subjects (observed cases=2, standardized incidence rate=101.9; 95% confidence interval: 25.5-407.4). Assuming a 100% 3-year study sensitivity for gastric cancer, faecal occult blood testing positive predictive value would be 0.4% (40-74 years) or 0.7% (> or =60 years) in faecal occult blood testing+/colonoscopy- subjects. CONCLUSIONS: Data suggest an association of faecal occult blood testing+/colonoscopy- and excess gastric cancer incidence in the following year. Due to low faecal occult blood testing+ positive predictive value, routine upper digestive tract endoscopy in these subjects is questionable.     

Randomized controlled trial of the impact of intensive patient education on compliance with fecal occult blood testing

BACKGROUND: Randomized controlled trials have demonstrated that fecal occult blood testing (FOBT) reduces colorectal cancer (CRC) mortality. However, patient compliance with FOBT is low and this is one of the major barriers to CRC screening. OBJECTIVE: To determine whether intensive patient education increases FOBT card return rates. DESIGN: Randomized controlled trial. SETTING: Department of Veterans Affairs primary care clinic. PARTICIPANTS: Seven hundred eighty-eight patients who were referred for FOBT. INTERVENTIONS: Patients were randomly allocated to receive either intensive (n=396) or standard (n=392) patient education. Patients in the intensive education group received a one-on-one educational session by primary care nurses on the importance of CRC screening, were instructed on how to properly collect stool specimens for FOBT, and were given a 2-page handout on CRC screening. Patients in the standard education group only received the FOBT cards and written instructions from the manufacturer on how to properly collect stool specimens for FOBT. RESULTS: Patients in the intensive education group were more likely to return the FOBT cards (65.9% vs 51.3%; P<.001) and called the clinic with additional questions less often (1.5% vs 5.9%; P=.001) than the standard education group. The median time to return the FOBT cards was significantly shorter in the intensive education group (36 vs 143 days; P<.001 by log-rank test). However, the proportion of patients who had a positive FOBT did not differ in the two groups (4.6% vs 6.0%; P=.51). CONCLUSIONS: Intensive patient education significantly improved patient compliance with FOBT. Future studies to evaluate additional educational strategies to further improve patient compliance with CRC screening are warranted.     

Barriers to colorectal cancer screening： A case-control study

AIM： To investigate barriers to colorectal cancer （CRC） screening in a community population. METHODS： We conducted a community-based case-control study in an urban Chinese population by questionnaire. Cases were selected from those completing both a fecal occult blood test （FOBT） case and colonoscopy in a CRC screening program in 2004. Control groups were matched by gender, age group and community. Control 1 included those having a positive FOBT but refusing a colonoscopy. Control 2 included those who refused both an FOBT and colonoscopy. RESULTS： The impact of occupation on willingness to attend a colorectal screening program differed by gender. P for heterogeneity was 0.009 for case vs control group 1, 0.01 for case versus control group 2, and 0.80 for control group 1 vs 2. Poor awareness of CRC and its screening program, characteristics of screening tests, and lack of time affected thescreening rate. Financial support, fear of pain and bowel preparation were barriers to a colonoscopy as a screening test. Eighty-two percent of control group 1 and 87.1% of control group 2 were willing attend if the colonoscopy was free, but only 56.3% and 53.1%, respectively, if it was self-paid. Multivariate odds ratios for case vs control group 1 were 0.10 among those unwilling to attend a free colonoscopy and 0.50 among those unwilling to attend a self-paid colonoscopy. CONCLUSION： Raising the public awareness of CRC and its screening, integrating CRC screening into the health care system, and using a painless colonoscopy would increase its screening rate.     

Clinicopathologic studies of immunologic fecal occult blood test for colorectal cancer

In our hospital, 83 patients with colorectal cancer underwent the immunologic fecal occult blood test (IFOBT). The positive rate for IFOBT in all patients was 87%. Colon cancers more proximal than the transverse colon were 100% positive. Carcinomas of the ulcerative type showed a significantly higher positive rate than those of the non-ulcerative type (94% vs 73%). Carcinomas penetrating the muscularis or beyond showed a significantly higher positive rate, of 96% (52/54 cases) compared to carcinomas confined to the mucosa or submucosa, which gave positive rates of 64% and 60%, respectively. In the investigation of the 7 patients with colorectal cancer who showed negative results on the IFOBT, IFOBT had been performed only once in of these patients. Accordingly, it was considered necessary to perform IFOBT more than once. The cancers in 5 of these 7 patients were found to be carcinomas confined to the mucosa. This result suggests the advisability of annual IFOBTs. It is also considered necessary to manage patients who show undefinable but possibly positive (±) results with caution.     

Long-term effect of faecal occult blood screening on incidence and mortality from colorectal cancer

BackgroundSeveral randomized trials have shown a reduction of colorectal cancer mortality by screening using guaiac-based faecal occult blood tests. However, little is known on the long-term effect of screening at the population level in everyday practice.MethodsSmall-sized geographic areas including a total of 91,199 individuals were allocated to either biennal screening using the Hemoccult-II test or no screening. The expected mortality and incidence in the cohort invited to screening was determined using mortality and incidence in the non-screened population.ResultsColorectal cancer mortality was significantly lower in the population invited to screening than in the non-screened population after 11 screening rounds (standardized mortality ratio: 0.87; 0.80–0.94). The standardized mortality ratio remained significant whatever the duration of follow-up. This reduction in colorectal cancer mortality was more pronounced in those who participated in the first screening campaign, who were regular participants in screening rounds (standardized mortality ratio: 0.67; 0.59–0.76). In contrast, colorectal cancer incidence was not different between the screened and non-screened populations (standardized incidence ratio: 1.01; 0.96–1.06).ConclusionOur findings confirm, in the long term, that screening with Hemoccult can reduce colorectal cancer mortality. The data also highlight the benefit of regular participation in screening and the absence of effect of screening on colorectal cancer incidence.     

Fecal occult blood and flexible sigmoidoscopy screening for colorectal cancer: modeling the impact on colonoscopy requirements and cancer detection rates

AiM: The aim of this study was to estimate the colonoscopy requirements and the likely impact of fecal occult blood and flexible sigmoidoscopy screening on the detection of colorectal cancer by using previously published data. METHODS: Fecal occult blood and flexible sigmoidoscopy screening programs were applied to the 2.04 million subjects aged 50-65 years, at a participation rate of 40%. The following strategies were evaluated: Fecal occult blood testing with colonoscopy follow up of all positive tests; flexible sigmoidoscopy with colonoscopy follow up of all adenomatous polyps; and flexible sigmoidoscopy with colonoscopy follow up of all adenomatous polyps > 10 mm in size. RESULTS: The fecal occult blood program detected 5.6% of all colorectal cancer cases at a rate of 2,914 colonoscopies/percentage of detection of colorectal cancer. The flexible sigmoidoscopy program detected 14% of all colorectal cancer cases at a rate of 8,160 colonoscopies/percentage of detection of colorectal cancer. The flexible sigmoidoscopy program with follow up of adenomatous polyps > 10 mm in size detected 13% of all colorectal cancer cases at a rate of 1,230 colonoscopies/percentage of detection of colorectal cancer. CONCLUSIONS: Flexible sigmoidoscopy screening followed by colonoscopic follow up of adenomatous polyps > 10 mm in size is the most efficient screening strategy in terms of colonoscopies generated and cases of colorectal cancer detected.