***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: The disease natural history of colorectal neoplasm regarding two opposing theories , adenoma – carcinoma sequence and de novo carcinoma theory , is controversial and rarely quantified . The aims of this study are therefore to estimate the dwelling times of adenoma – carcinoma sequence by adenoma size and histological type , taking de novo carcinoma into account . The efficacy of polypectomy  was therefore estimated making allowance for two pathways . A case – cohort design , underpinning a cohort with 13 908 subjects ( including 10 496 normal subjects , 2652 polyps , 760 colorectal cancers ) who underwent the first examination of colonoscopy between 1979 and 1998 , was devised to estimate parameters associated with two opposing theories by r and omly selecting 305 normal subjects , 300 patients with polyps , and 116 colorectal cancers from the cohort . All the 2652 polyps were linked to national cancer registry to ascertain 25 invasive carcinomas after polypectomy . For the five-state model associated with adenoma size , dwelling times of small ( 0.6–1 cm ) and large adenoma ( > 1 cm ) are 7.75 and 5.27 years for the model without considering de novo , and 17.48 and 15.90 years for the model taking de novo carcinoma into account . Similar findings are observed for the model associated with histological type . The estimated proportions of de novo carcinoma are 31.87 % from the model by adenoma size and 27.81 % from the model by histological type . Compared to size less than 5 mm , patients with adenoma size between 6 and 10 mm and patients with adenoma size larger than 1 cm have 2.17-fold ( 0.67–10.74 ) and 4.25-fold ( 1.23–14.70 ) , respectively , for the risk of malignant transformation . There are similar findings for the model by histological type . The estimates of overall efficacy of colonoscopy in reducing CRC is 73 % for the model allowing for de novo carcinoma and 88 % for the model without considering de novo carcinoma theory . The efficacy of diminutive adenoma and small adenoma increases with follow-up years , whereas the efficacy of large adenoma decreases with follow-up years . In conclusion , about 30 % of cancers arising from de novo sequence are demonstrated . This finding , together with the adenoma – carcinoma sequence associated with adenoma size and histological type , is important for the estimation of dwelling times , the efficacy of colonoscopy , and the surveillance of polyp after polypectomy In a prospect i ve necropsy study of the large bowel in 365 cases , the commonest polyp identified was the hyperplastic ( metaplastic ) variety , of which 86.1 % of the total were located in the rectum . The other main type of polyp found , and of much greater importance because of its malignant potential , was the neoplastic adenoma . These were present , either singly or multiply , in 73 of 198 male cases ( 36.9 % ) and in 48 of 167 female cases ( 28.7 % ) . Their prevalence and their tendency to be multiple rose with increasing age in both sexes . Most adenomas had a tubular growth pattern and 88.8 % of these were under 1 cm in diameter . There was a fairly even distribution of adenomas throughout the large bowel but a higher proportion of adenomas over 1 cm in diameter occurred in the caecum , sigmoid colon , and rectum than at other sites . In the whole series nine adenocarcinomas were present , two of which were arising in adenomas CONTEXT Conventional colonoscopy is the best available method for detection of colorectal cancer ; however , it is invasive and not without risk . Computed tomographic colonography ( CTC ) , also known as virtual colonoscopy , has been reported to be reasonably accurate in the diagnosis of colorectal neoplasia in studies performed at expert centers . OBJECTIVE To assess the accuracy of CTC in a large number of participants across multiple centers . DESIGN , SETTING , AND PARTICIPANTS A nonr and omized , evaluator-blinded , noninferiority study design of 615 participants aged 50 years or older who were referred for routine , clinical ly indicated colonoscopy in 9 major hospital centers between April 17 , 2000 , and October 3 , 2001 . The CTC was performed by using multislice scanners immediately before st and ard colonoscopy ; findings at colonoscopy were reported before and after segmental unblinding to the CTC results . MAIN OUTCOME MEASURES The sensitivity and specificity of CTC and conventional colonoscopy in detecting participants with lesions sized at least 6 mm . Secondary outcomes included detection of all lesions , detection of advanced lesions , possible technical confounders , participant preferences , and evidence for increasing accuracy with experience . RESULTS A total of 827 lesions were detected in 308 of 600 participants who underwent both procedures ; 104 participants had lesions sized at least 6 mm . The sensitivity of CTC  for detecting participants with 1 or more lesions sized at least 6 mm was 39.0 % ( 95 % confidence interval [ CI ] , 29.6%-48.4 % ) and for lesions sized at least 10 mm , it was 55.0 % ( 95 % CI , 39.9%-70.0 % ) . These results were significantly lower than those for  conventional colonoscopy  , with sensitivities of 99.0 % ( 95 % CI , 97.1%->99.9 % ) and 100 % , respectively . A total of 496 participants were without any lesion sized at least 6 mm . The specificity of CTC and conventional colonoscopy  for detecting participants without any lesion sized at least 6 mm was 90.5 % ( 95 % CI , 87.9%-93.1 % ) and 100 % , respectively , and without lesions sized at least 10 mm , 96.0 % ( 95 % CI , 94.3%-97.6 % ) and 100 % , respectively . Computed tomographic colonography missed 2 of 8 cancers . The accuracy of CTC  varied considerably between centers and did not improve as the study progressed . Participants expressed no clear preference for either technique . CONCLUSIONS Computed tomographic colonography by these methods is not yet ready for widespread clinical application . Techniques and training need to be improved BACKGROUND , AIMS , AND PATIENTS : In a prospect i ve follow up and intervention study of colorectal polyps , leaving all polyps less than 10 mm in situ for three years , analysis of redetection rate , growth , and new polyp formation was carried out in 116 patients undergoing annual colonoscopy .  The findings in relation to growth and new polyp formation were applied to 58 subjects who received placebo .  RESULTS : Redetection rate varied from 75 - 90 % for each year , and was highest in the rectum and sigmoid colon . There was no net change in size of all polyps in the placebo group , however , polyps less than 5 mm showed a tendency to net growth , and polyps 5 - 9 mm a tendency to net regression in size , both for adenomas and hyperplastic polyps . This pattern was verified by computerised image analysis . Patients between 50 and 60 years showed evidence of adenoma size increase compared with the older patients , and the same was true for those with multiple adenomas ( four to five ) compared with those with a single adenoma . The new adenomas were significantly smaller and 71 % were located in the right side of the colon . Patients with multiple adenomas had more new polyps at all the follow up examinations than patients with a single adenoma . One patient developed an invasive colorectal carcinoma , which may be evolved from a previously overlooked polyp . Two polyps , showing intramucosal carcinoma after follow up for three years , were completely removed , as judged by endoscopy and histological examination . CONCLUSIONS : The results show that follow up of unresected colorectal polyps up to 9 mm is safe . The consistency of growth retardation of medium sized polyps suggests extended intervals between the endoscopic follow up examinations , but the increased number of new polyps in the proximal colon indicates total colonoscopy as the examination of choice . The growth retardation of the medium sized polyps may partly explain the discrepancy between the prevalence of polyps and the incidence of colorectal cancer BACKGROUND & AIMS The miss rate of colonoscopy for neoplasms is poorly understood . The aim of this study was to determine the miss rate of colonoscopy by same day back-to-back colonoscopy . METHODS Two consecutive same day colonoscopies were performed in 183 patients . The patients were r and omized to undergo the second colonoscopy by the same or a different endoscopist and in the same or different position . RESULTS The overall miss rate for adenomas was 24 % , 27 % for adenomas < or = 5 mm , 13 % for adenomas 6 - 9 mm , and 6 % for adenomas > or = 1 cm . Patients with two or more adenomas at the first examination were more likely than patients with no or one adenoma detected at the first examination to have one or more adenomas at the second examination ( odds ratio , 3.3 ; 95 % confidence interval , 1.69 - 6.46 ) . Right colon adenomas were missed more often ( 27 % ) than left colon adenomas ( 21 % ) , but the difference was not significant . There was evidence of variation in sensitivity between endoscopists , but significant miss rates for small adenomas were found among essentially all endoscopists . CONCLUSIONS Using current colonoscopic technology , there are significant miss rates for adenomas < 1 cm even with meticulous colonoscopy . Miss rates are low for adenomas > or = 1 cm . The results suggest the need for improvements in colonoscopic technology CONTEXT The Framingham Heart Study produced sex-specific coronary heart disease ( CHD ) prediction functions for assessing risk of developing incident CHD in a white middle-class population . Concern exists regarding whether these functions can be generalized to other population s. OBJECTIVE To test the validity and transportability of the Framingham CHD prediction functions per a National Heart , Lung , and Blood Institute workshop organized for this purpose . DESIGN , SETTING , AND SUBJECTS Sex-specific CHD functions were derived from Framingham data for prediction of coronary death and myocardial infa rct ion . These functions were applied to 6 prospect ively studied , ethnically diverse cohorts ( n = 23 424 ) , including whites , blacks , Native Americans , Japanese American men , and Hispanic men : the Atherosclerosis Risk in Communities Study ( 1987 - 1988 ) , Physicians ' Health Study ( 1982 ) , Honolulu Heart Program ( 1980 - 1982 ) , Puerto Rico Heart Health Program ( 1965 - 1968 ) , Strong Heart Study ( 1989 - 1991 ) , and Cardiovascular Health Study ( 1989 - 1990 ) . MAIN OUTCOME MEASURES The performance , or ability to accurately predict CHD risk , of the  Framingham functions  compared with the performance of risk functions developed specifically from the individual cohorts ' data . Comparisons included evaluation of the e quality of relative risks for st and ard CHD risk factors , discrimination , and calibration . RESULTS For white men and women and for black men and women the Framingham functions performed reasonably well for prediction of CHD events within 5 years of follow-up . Among Japanese American and Hispanic men and Native American women , the Framingham functions systematic ally overestimated the risk of 5-year CHD events . After recalibration , taking into account different prevalences of risk factors and underlying rates of developing CHD , the Framingham functions worked well in these population s. CONCLUSIONS The sex-specific Framingham CHD prediction functions perform well among whites and blacks in different setting s and can be applied to other ethnic groups after recalibration for differing prevalences of risk factors and underlying rates of CHD events The data of the National Polyp Study , a large longitudinal study on surveillance of adenoma patients , is used for testing assumptions on the adenoma‐carcinoma sequence . The observed adenoma and colorectal cancer incidence in the National Polyp Study were compared with the simulated outcomes of the MISCAN‐COLON model of epidemiology and control of colorectal cancer for the U.S. population based on expert opinion . Variants of this model were explored in order to identify assumptions on the adenoma‐carcinoma sequence that are consistent with the study observations . The high observed adenoma detection rates at surveillance and low observed colorectal cancer incidence in the National Polyp Study could only be explained by assuming a high incidence rate of adenomas accompanied by regression of adenomas . The National Polyp Study data suggest that adenoma prevalence results from a dynamic process of both formation as well as regression of adenomas . This lowers the expectations for the effects of colorectal cancer screening strategies that focus on adenoma detection . © 2004 Wiley‐Liss , BACKGROUND & AIMS In a population reflective of a screening setting , our aim was to compare the relative sensitivity and specificity of computed tomography ( CT ) colonography with double-contrast barium enema ( DCBE ) for detection of colorectal polyps and to assess the added value of double reading at CT colonography , using endoscopy as the arbiter . METHODS This prospect i ve , blinded study comprised 837 asymptomatic persons at higher than average risk for colorectal cancer who underwent CT colonography followed by same-day DCBE .  Examinations with polyps > or = 
    Output:
    
CT colonography with CAD for inexperienced readers was more clinical ly effective and cost-effective than FS .
The addition of CAD to CT colonography screening improves the CRC prevention rate , result ing in advantageous cost-effectiveness for screening .