***TASK*** the task is to summarize an input biomedical literature in six sentences 
    ***INPUT*** the input is a biomedical literature 
    ***OUTPUT*** the output is the summary of an input biomedical literature in six sentences 
    ***DOCUMENTATION*** 
    ***EXAMPLES*** 
    Input: Despite recent declines in both incidence and mortality ( 1 ) , colorectal cancer remains the second most common cause of death from cancer in the United States ( 2 ) . Screening for colorectal cancer reduces mortality by allowing physicians to detect cancer at earlier , more treatable stages , as well as to identify and remove adenomatous polyps ( asymptomatic benign precursor lesions that may lead to colorectal cancer ) . Many tests are available for screening , such as fecal occult blood tests ( FOBTs ) , flexible sigmoidoscopy , and colonoscopy . Screening with FOBT ( Hemoccult II , Beckman Coulter , Fullerton , California ) has been shown to reduce colorectal cancer mortality by 15 % to 33 % in r and omized , controlled trials ( 35 ) , and screening with more sensitive FOBTs , flexible sigmoidoscopy , colonoscopy , or combinations of these tests may reduce the burden of colorectal cancer even more ( 6 , 7 ) . In the absence of adequate clinical trial data on several recommended screening strategies , microsimulation modeling can provide guidance on the risks , benefits , and testing re sources required for different screening strategies to reduce the burden of colorectal cancer . In July 2002 , the U.S. Preventive Services Task Force ( USPSTF ) concluded that there was sufficient evidence to recommend strongly that all average-risk adults 50 years of age or older should be offered colorectal cancer screening ( 8) . However , the logistics of screening , such as the type of screening test , screening interval , and age at which to stop screening , were not evaluated in terms of the balance of benefits and potential harms . The USPSTF has again addressed recommendations for colorectal cancer screening with a systematic review of the evidence ( 9 ) on screening tests . For this assessment , the USPSTF requested a decision analysis to project expected outcomes of various strategies for colorectal cancer screening . Two independent microsimulation modeling groups from the Cancer Intervention and Surveillance Modeling Network ( CISNET ) , funded by the National Cancer Institute , used a comparative modeling approach to compare life-years gained relative to re source use of different strategies for colorectal cancer screening . Methods We used 2 microsimulation models  , MISCAN ( MIcrosimulation Screening Analysis ) ( 1012 ) and SimCRC ( Simulation Model of Colorectal Cancer ) ( 13 ) , to estimate the life-years gained relative to no screening and the colonoscopies required ( that is , an indicator for re source use and risk for complications ) for different colorectal cancer screening strategies defined by test , age at which to begin screening , age at which to stop screening , and screening interval . We aim ed to identify a set of recommendable strategies with similar clinical benefit and an efficient use of colonoscopy re sources . Using 2 models ( that is , a comparative modeling approach ) adds credibility to the results and serves as a sensitivity analysis on the underlying structural assumptions of the models , particularly pertaining to the unobservable natural history of colorectal cancer . Microsimulation Models The Appendix describes the MISCAN and SimCRC models , and st and ardized model profiles are available at cisnet.cancer.gov/profiles/. In brief , both models simulate the life histories of a large population of individuals from birth to death . As each individual ages , there is a chance that an adenoma will develop . One or more adenomas can occur in an individual , and each adenoma can independently develop into pre clinical ( that is , undiagnosed ) colorectal cancer ( Figure 1 ) . The risk for developing an adenoma depends on age , sex , and baseline individual risk . The models track the location and size of each adenoma ; these characteristics influence disease progression and the chance that the adenoma will be found by screening . The size of adenomas can progress from small ( 5 mm ) to medium ( 6 to 9 mm ) to large ( 10 mm ) . Some adenomas eventually become malignant , transforming to stage I pre clinical cancer . Pre clinical cancer has a chance of progressing through stages I to IV and may be diagnosed by symptoms at any stage . Survivorship after diagnosis depends on the stage of disease . Figure 1 . Natural history of disease as modeled by the Microsimulation Screening Analysis and Simulation Model of Colorectal Cancer models . The opportunity to intervene in the natural history through screening is noted . The natural history component of each model was calibrated to 19751979 clinical incidence data ( 14 ) and adenoma prevalence from autopsy studies in the same period ( 1524 ) . We used this period because incidence rates and adenoma prevalence had not yet been affected by screening . We corrected the adenoma prevalence for studies of non-U.S. population s by using st and ardized colorectal cancer incidence ratios . The models use all-cause mortality estimates from the U.S. life tables and stage-specific data on colorectal cancer survival from the 19961999 Surveillance , Epidemiology , and End Results program ( 14 ) . Table 1 compares outcomes from the natural history components of the models . Table 1 . Comparison of the Natural History Outcomes from the Microsimulation Screening Analysis ( MISCAN ) and Simulation Model of Colorectal Cancer ( SimCRC ) Models The effectiveness of a screening strategy is modeled through a test 's ability to detect lesions ( that is , adenomas or pre clinical cancer ) . Once screening is introduced , a simulated person who has an underlying lesion has a chance of having it detected during a screening round depending on the sensitivity of the test for that lesion and whether the lesion is within the reach of the test . Screened persons without an underlying lesion can have a false-positive test result and undergo unnecessary follow-up colonoscopy . Hyperplastic polyps are not modeled explicitly , but their detection is reflected in the specificity of the screening tests . The models incorporate the risk for fatal complications associated with perforation during colonoscopy . Both models have been vali date d against the long-term reductions in incidence and mortality of colorectal cancer with annual FOBT reported in the Minnesota Colon Cancer Control Study ( 3 , 25 , 26 ) and show good concordance with the trial results . Strategies for Colorectal Cancer Screening In consultation with the USPSTF , we included the following basic strategies : 1 ) no screening , 2 ) colonoscopy , 3 ) FOBT ( Hemoccult II , Hemoccult SENSA [ Beckman Coulter ] , or fecal immunochemical testing ) , 4 ) flexible sigmoidoscopy ( with biopsy ) , and 5 ) flexible sigmoidoscopy combined with Hemoccult SENSA . For each basic strategy , we evaluated start ages of 40 , 50 , and 60 years and stop ages of 75 and 85 years . For the FOBT strategies , we considered screening intervals of 1 , 2 , and 3 years , and for the sigmoidoscopy and colonoscopy strategies , we considered intervals of 5 , 10 , and 20 years . These variations result ed in 145 strategies : 90 single-test strategies , 54 combination-test strategies , and 1 no-screening strategy . The stop age reflects the oldest possible age at which to screen , but the actual stopping age is dictated by the start age and screening interval . In the base case , we assumed 100 % adherence for screening tests , follow-up of positive findings , and surveillance of persons found to have adenomas . Individuals with a positive FOBT result or with an adenoma detected by sigmoidoscopy were referred for follow-up colonoscopy . For years in which both tests were due for the combined strategy , the FOBT was performed first ; if the result was positive , the patient was referred for follow-up colonoscopy . In those years , flexible sigmoidoscopy was done only for patients with a negative FOBT result . If findings on follow-up colonoscopy were negative , the individual was assumed to undergo subsequent screening with colonoscopy with a 10-year interval ( as long as results of the repeated colonoscopy were negative ) and did not return to the initial screening schedule , as is the recommendation of the U.S. Multi-Society Task Force and American Cancer Society ( 7 , 27 ) . All individuals with an adenoma detected were followed with colonoscopy surveillance per the Multi-Society guidelines ( 27 , 28 ) . The surveillance interval depended on the number and size of the adenomas detected on the last colonoscopy ; it ranged from 3 to 5 years and was assumed to continue for the remainder of the person 's lifetime . We estimated the test characteristics of colorectal cancer screening from a review of the available literature ( Table 2 ) ( 29 ) . We conducted this review independently of and parallel in time with the systematic evidence review performed for the USPSTF ( 9 ) . Table 2 . Test Characteristics Used in the Microsimulation Screening Analysis and Simulation Model of Colorectal Cancer Models Evaluation of Outcomes Determination of Efficient Strategies The most effective strategy was defined as the one with the greatest life-years gained relative to no screening . However , it is important to consider the relative intensity of test use required to achieve those gains . The more effective strategies tended to be associated with more colonoscopies on average in a person 's lifetime , which translated into an increased risk for colonoscopy-related complications . We used an approach that mirrors that of cost-effectiveness analysis ( 30 ) to identify the set of efficient , or dominant , strategies within each test category . A strategy was considered dominant when no other strategy or combination of strategies provided more life-years with the same number of colonoscopies . We conducted this analysis separately for each of the 5 basic screening strategies because the number of noncolonoscopy tests differed by strategy . We then ranked the efficient screening strategies by increasing effectiveness and calculated the incremental number of colonoscopies ( COL ) per 1000 , the incremental life-years gained ( LYG ) per 1000 , and the incremental number of colonoscopies necessary to achieve 1 year of life ( BACKGROUND Indirect evidence and modeling analyses suggest that colonoscopy may be the most cost-effective way to screen the average-risk population for colorectal neoplasia . However , the success and safety of primary colonoscopic screening has not been prospect ively evaluated in a multicenter trial . METHODS Asymptomatic subjects age 50 to 75 years who had not undergone examination of the colon within 10 years were recruited from the general medicine clinics of 13 Department of Veterans Affairs Medical Centers . Eligible patients underwent colonoscopy by study coinvestigators , at which time all polyps were measured , photographed , and removed . Patients were contacted at 24 hours and 1 week to track procedure-related complications . RESULTS Primary screening colonoscopy was performed in a cohort of 3196 asymptomatic subjects . A " good " preparation was reported in 81 % of patients , and colonoscopy to the cecum was successful in 97.2 % of cases . Mean insertion time to the cecum and total procedure times were 10.5 ( 8.7 ) and 30.6 ( 19.1 ) minutes , respectively . No preprocedural patient characteristics were identified that were predictive of an incomplete procedure . At least one polyp was resected in 1672 patients . There was no perforation and no death attributed to colonoscopy .  Major morbidity considered to be definitely related to colonoscopy occurred in 9 of 3196 procedures ( 0.3 % ) : lower GI bleeding requiring intervention ( 6 ) , myocardial infa rct ion and /or cerebrovascular accident ( 2 ) , and thrombophlebitis ( 1 ) . In subjects undergoing only diagnostic procedures , the major complication rate was 0.1 % . CONCLUSIONS Screening colonoscopy can be performed in multiple centers with a high degree of success and safety in large numbers of asymptomatic , average-risk men Aim : Our aim was to perform a prospect i ve evaluation of the frequency and diagnostic consequences of extracolonic findings at multidetector array computed tomography colonography ( MDCTC ) in asymptomatic patients undergoing surveillance for former colorectal polyps or cancer . Patients and methods : Seventy five consecutive patients undergoing surveillance for former colorectal cancer ( CRC ) or large bowel adenoma were examined with MDCTC . Two independent observers evaluated the images with regard to extracolonic findings . Patient records and radiological information systems were review ed to determine the results and consequences of the workup derived from MDCTC . Results : Sixty five per cent ( 95 % confidence interval ( CI ) 55–73 % ) of patients had extracolonic abnormalities and in 12 % ( CI 7–18 % ) of patients additional workup was indicated . Two patients ( 3 % ( CI 1–6 % ) ) underwent surgery because of the findings ( one ) or because of complications of the workup ( one ) . Conclusion : MDCTC identifies a large number of extracolonic findings . Approximately 12 % of asymptomatic patients undergo additional workup , of benefit to only a few . The high prevalence of extracolonic findings may make MDCTC a problematic colorectal screening tool for both ethical and economic reasons BACKGROUND Computed tomographic ( CT ) colography ( virtual colonoscopy ) is a new imaging method for detection of colon polyps and cancer . OBJECTIVE To evaluate the sensitivity of CT colography for polyp detection in a population without symptoms that included persons without colon neoplasia and with radiologists blinded to colonoscopic findings . METHODS Forty-six persons without symptoms underwent spiral CT followed by same-day colonoscopy with subsequent inspection of two-dimensional axial CT images , interactive multiplanar images , and surfaced and volume-rendered images of the colon ( three-dimensional CT colography ) . RESULTS Three-dimensional CT colography was superior to two-dimensional axial imaging for detection of colon polyps .  Three-dimensional CT colography depicted 
    Output:
    
a.  Flexible sigmoidoscopy , b. Colonoscopy , c. Computed tomographic ( CT ) colonography , d. Fecal screening tests :  i. High-sensitivity guaiac fecal occult blood test ( FOBTs ) ; ii .
Fecal immunochemical test ; iii .