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

Diversity of model approaches for breast cancer screening: a review of model assumptions by The Cancer Intervention and Surveillance Network (CISNET) Breast Cancer Groups

The National Cancer Institute-sponsored Cancer Intervention and Surveillance Network program on breast cancer is composed of seven research groups working largely independently to model the impact of screening and adjuvant therapy on breast cancer mortality trends in the US from 1975 to 2000. Each of the groups has chosen a different modeling methodology without purposeful attempt to be in contrast with each other. The seven groups have met biannually since November 2000 to discuss their methodology and results. This article investigates the differences in methodology. To facilitate this comparison, each of the groups submitted a description of their model into a uniformly structured web based ‘model profiler’. Six of the seven models simulate a preclinical natural history that cannot be observed directly with parameters estimated from published evidence concerning screening and therapy effects. The remaining model regards published evidence on intervention effects as prior information and updates that with information from the US population in a Bayesian type analysis. In general, the differences between the models appear to be small, particularly among the models driven by natural history assumptions. However, we demonstrate that such apparently small differences can have a large impact on surveillance of population trends. We describe a systematic approach to evaluating differences in model assumptions and results, as well as differences in modeling culture underlying the differences in model structure and parameters.

Evaluation of flexible sigmoidoscopy as an investigation for "left sided" colorectal symptoms

BACKGROUND

Colonoscopy is the best way of imaging the colon with concurrent biopsy and treatment. However it is expensive, requires full bowel preparation, and carries a risk of complications. Flexible sigmoidoscopy is an alternative way to investigate symptoms that raise the suspicion of a lesion of the rectum or left colon.

AIM OF THE STUDY

To evaluate flexible sigmoidoscopy as the main investigation for "left sided" colorectal symptoms.

METHODS

The clinical records of 317 patients who were assessed at a colorectal specialist clinic and were thought to have a suspicion of a lesion of the rectum or left colon were retrospectively reviewed. All patients had flexible sigmoidoscopy as the primary investigation. Primary outcome was the diagnostic yield of flexible sigmoidoscopy and secondary outcomes were any additional colonic investigations required, failure rates, and complication rates.

RESULTS

Three hundred and sixteen patients who had flexible sigmoidoscopy with the above criteria were retrospectively analysed. Twenty four procedures (7.6%) had to be abandoned because of poor bowel preparation. The examination was considered complete when it reached the splenic flexure, which was the case in 205 cases (65%). In 137 flexible sigmoidoscopies (43.3%) there were no abnormal findings. Of the remaining 179 a carcinoma of the rectum or colon was found in 28 cases (8.8%) and one or more polyps was found in 57 (18%) cases. On the basis of the findings it was calculated that 31% of the patients would require an additional investigation for further imaging of the right colon.

DISCUSSION

Although flexible sigmoidoscopy has a high yield of pathologies when carried out by a specialist colorectal clinic, the presence of those pathologies makes the full imaging of the whole colon with an additional investigation necessary. Therefore the cost efficiency of flexible sigmoidoscopy is questionable. Although flexible sigmoidoscopy is indicated for certain patients, it cannot replace colonoscopy as the main investigation used by a specialist colorectal clinic.

Cost-effectiveness of colorectal cancer screening: comparison of community-based flexible sigmoidoscopy with fecal occult blood testing and colonoscopy

BACKGROUND AND AIMS

To determine the cost-effectiveness of screening for colorectal cancer using flexible sigmoidoscopy once every 10 years, compared with annual and biennial rehydrated Hemoccult fecal occult blood testing and colonoscopy once every 10 years, or no screening.

METHODS

A Markov model was developed in order to simulate the progression of a cohort of asymptomatic, average-risk individuals aged 55-64 years who were moving through a defined series of states towards death. The main outcome measures were: cases of colorectal cancer averted, colorectal cancer deaths averted, and cost per life-year saved.

RESULTS

Colonoscopy averted the greatest number of cases of colorectal cancer (35%), followed by flexible sigmoidoscopy (25%), and annual (24%) and biennial (14%) fecal occult blood testing. Colonoscopy averted the greatest number of deaths from colorectal cancer (31%), followed by annual fecal occult blood testing (29%), flexible sigmoidoscopy (21%) and biennial fecal occult blood testing (19%). Flexible sigmoidoscopy was the most efficient in terms of cost per life-year saved (16,801 Australian dollars), followed by colonoscopy (19,285 Australian dollars), biennial (41,183 Australian dollars), and annual (46,900 Australian dollars) fecal occult blood testing.

CONCLUSIONS

Flexible sigmoidoscopy and colonoscopy are cost-effective strategies for reducing the disease burden of colorectal cancer.

Flexible sigmoidoscopy screening for colorectal neoplasia in average-risk people: evaluation of a five-year rescreening interval

OBJECTIVE

To determine the prevalence of colorectal neoplasia detected by rescreening people with average risk five years after initial screening by flexible sigmoidoscopy.

DESIGN

Prospective survey of results of a colorectal cancer screening program.

PARTICIPANTS

People aged 55-64 years with no symptoms or family history of colorectal cancer who were recruited from the community for flexible sigmoidoscopy screening five years previously (July 1995 to December 1996) and had no colorectal neoplasms detected.

SETTING

Fremantle Hospital, Western Australia, a community-based teaching hospital, December 2000 to June 2001.

MAIN OUTCOME MEASURES

Number and size of colorectal neoplasms (adenomas or cancer) compared between rescreened patients and initial screening population (all 982 people screened between July 1995 and December 1996).

RESULTS

803 people were eligible for rescreening; 138 were no longer at the recorded address, and 361 of the remaining 665 (54%) were rescreened. Rescreening found a significantly lower prevalence of colorectal adenomas than initial screening (8% [95% CI, 5%-11%] versus 14% [95% CI, 13%-15%]; P < 0.05) and also a lower percentage of adenomatous polyps over 5 mm in diameter (32% [95% CI, 15%-49%] versus 51% [95% CI, 46%-56%]; no significant difference).

CONCLUSION

Average-risk people who have been screened for colorectal neoplasms, with none found, have a low prevalence of neoplastic lesions five years later. Longer rescreening intervals need to be considered.