***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: BACKGROUND / AIMS The inherited susceptibility to hereditary nonpolyposis colorectal cancer ( HNPCC ) provides an opportunity for secondary prevention of colorectal cancer ( CRC ) in family members who are at 50 % lifetime risk . The aim of this study was to evaluate the effectiveness of long-term screening during a 10-year period . METHODS The CRC and death rates were compared between two groups of asymptomatic at-risk members of 22 families with HNPCC : 133 subjects screened at 3-year intervals by colonoscopy or barium enema and sigmoidoscopy and 118 control subjects without screening .  The screening was complete in 118 subjects ( 89 % ) , whereas 18 control subjects ( 15 % ) had screening examinations outside of the study . RESULTS CRC occurred in 6 study subjects ( 4.5 % ) and in 14 controls ( 11.9 % ; P = 0.03 ) , a difference of 7.4 % in favor of the study group , which corresponds to a reduction by 62 % that is presumably because of polypectomies . The tumor stage was more favorable in the screening group with no deaths caused by CRC compared with 5 of 14 cases in controls . Overall , there were 6 and 12 deaths within the 10-year period in the study and control groups , respectively ( P = 0.08 ) . CONCLUSIONS The 3-year interval screening more than halves the CRC rate in at-risk members of families with HNPCC and seems to prevent CRC deaths BACKGROUND : The role of screening colonoscopy for colorectal ( CR ) neoplasia in average-risk population , remains to be determined . OBJECTIVES : To evaluate the prevalence and anatomic location of CR adenoma and carcinoma and the morbidity of colonoscopy  in individuals at average risk for CR cancer ( CRC ) . METHODS : A retrospective prevalence study of subjects aged 40–80 yr , with no cancer-related symptoms , personal or family history of CR neoplasia , who underwent a colonoscopy .  RESULTS : Enrolled were 1,177 persons ; 183 aged 40–49 yr ( young ) , 917 aged 50–75 yr , and 77 aged 76–80 yr ( elderly ) . The prevalence of overall CR neoplasia , advanced neoplasia , and cancer was 20.9 % , 6.3 % , and 1.1 % , respectively . In the 50–75 age group , the prevalence of overall adenoma , advanced neoplasia , and cancer was 21.3 % , 6.7 % , and 1.2 % , respectively . Of the 206 neoplasia cases , 21–43 % harbored proximal neoplasia beyond the reach of sigmoidoscopy , without distal lesions . Among the elderly , the prevalence of overall adenoma , advanced neoplasia , and cancer reached 26.0 % , 14.3 % , and 2.6 % , respectively . In the young group , 9.8 % had overall neoplasia , 1.1 % had advanced adenoma , and none had CRC . Procedure-related morbidity rate was 0.1 % , with no perforations , bleedings , or mortality . CONCLUSIONS : Screening colonoscopy in average-risk subjects demonstrated a considerable prevalence of CR neoplasia and proximal lesions beyond the reach of sigmoidoscopy . The morbidity rate was negligible . Primary screening colonoscopy should be considered in health programs for the average-risk population , beginning at the age of 50 yr . The significantly high rate of advanced and proximal neoplasia in the elderly , encourages the inclusion of healthy subjects aged 76–80 yr in future prospect i ve studies BACKGROUND Although tests for occult blood in the feces are widely used to screen for colorectal cancers , there is no conclusive evidence that they reduce mortality from this cause . We evaluated a fecal occult-blood test  in a r and omized trial and documented its effectiveness . METHODS We r and omly assigned 46,551 participants 50 to 80 years of age to screening for colorectal cancer once a year , to  screening every two years , or to a control group .  Participants who were screened su bmi tted six guaiac-impregnated paper slides with two smears from each of three consecutive stools . About 83 percent of the slides were rehydrated . Participants who tested positive underwent a diagnostic evaluation that included colonoscopy .  Vital status was ascertained for all study participants during 13 years of follow-up . A committee determined causes of death . A single pathologist determined the stage of each tissue specimen . Differences in mortality from colorectal cancer , the primary study end point , were monitored with the sequential log-rank statistic . RESULTS The 13-year cumulative mortality per 1000 from colorectal cancer was 5.88 in the annually screened group ( 95 percent confidence interval , 4.61 to 7.15 ) , 8.33 in the biennially screened group ( 95 percent confidence interval , 6.82 to 9.84 ) , and 8.83 in the control group ( 95 percent confidence interval , 7.26 to 10.40 ) . The rate in the annually screened group , but not in the biennially screened group , was significantly lower than that in the control group . Reduced mortality in the annually screened group was accompanied by improved survival in those with colorectal cancer and a shift to detection at an earlier stage of cancer . CONCLUSIONS Annual fecal occult-blood testing with rehydration of the sample s decreased the 13-year cumulative mortality from colorectal cancer by 33 percent Objective : This is the first study to evaluate the association between colonic screening and  colorectal cancer risk among Canadians . Methods : A case – control study was conducted . Cases were diagnosed with cancer of the colorectum , between 1997 and 2000 , aged 20 to 74 years , identified through the population -based Ontario Cancer Registry and recruited by the Ontario Familial Colorectal Cancer Registry . Controls were a sex- and age-matched r and om sample of the population of Ontario . 971 cases and 1944 controls completed question naires ( including colorectal screening history and many risk factors ) . Multivariate logistic regression analysis was used to obtain adjusted odds ratios ( OR ) estimates . Results : Having had a fecal occult blood screen was associated with reduced colorectal cancer risk ( OR=0.76 ; 95 % confidence interval ( CI ) : 0.59 , 0.97 ) . Having had a screening sigmoidoscopy was associated with a halving of colorectal cancer risk ( OR = 0.52 ; 95 % CI : 0.34 , 0.80 ) . Having had a screening colonoscopy did not significantly reduce colorectal cancer risk ( OR = 0.69 ; 95 % CI : 0.44 , 1.07 ) ; however , having had either screening endoscopy was associated with a significant reduction in colorectal cancer risk ( OR = 0.62 ; 95 % CI : 0.44 , 0.87 ) . Findings differed slightly by anatomic sub-site ( proximal and distal colorectum ) . Conclusions : We report a reduction in colorectal cancer risk  among persons who underwent colorectal cancer screening ; in particular , sigmoidoscopy . Findings are of great importance for the prevention of colorectal cancer BACKGROUND Variations in colonoscopy practice exist , which may be related to healthcare quality . AIMS To determine factors associated with three performance indicators of colonoscopy : complete colonoscopy , adenomatous polyp diagnosis , and duration . PATIENTS Consecutive patients referred for colonoscopy from 21 centres in 11 countries . METHODS This prospect i ve observational study used multiple variable regression analyses to identify determinants of the quality indicators . RESULTS Six thous and and four patients were included in the study . Patients from private , open-access centres ( odds ratio : 3.17 , 95 % confidence interval : 1.87 - 5.38 ) were more likely to have a  complete colonoscopy  than patients from public , gatekeeper centres . Patients from centres where over 50 % of the endoscopists were of senior rank were roughly twice as likely to have an adenoma diagnosed , and longer average withdrawal duration ( odds ratio : 1.08 , 95 % confidence interval : 1.07 - 1.09 ) was associated with more frequent adenoma diagnoses . Patients who had difficulty during colonoscopy had longer duration s to caecum ( time ratio : 2.87 , 95 % confidence interval : 2.72 - 3.01 ) and withdrawal duration s ( time ratio : 1.26 , 95 % confidence interval : 1.18 - 1.33 ) than patients who had no difficulties . CONCLUSIONS Multiple factors have been identified as being associated with key quality indicators . The non-modifiable factors permit the identification of patients who may be at greater risk of not having quality colonoscopy , while changes to the modifiable factors may help improve the quality of colonoscopy BACKGROUND This r and omised controlled trial is examining the hypothesis that a single flexible sigmoidoscopy screening offered at around age 60 years can lower the incidence and mortality of  colorectal cancer .  We report here on acceptability , safety , feasibility , and yield . METHODS Men and women aged 55 - 64 years , in 14 UK centres , who responded to a mailed question naire that they would attend for flexible sigmoidoscopy screening if invited , were r and omly assigned screening or control ( ratio one to two ) . The control group was not contacted . Small polyps were removed during screening , and colonoscopy was undertaken if high-risk polyps ( three or more adenomas , size 1 cm or greater , villous , severely dysplastic , or malignant ) were found . FINDINGS Of 354,262 people asked about their interest in having flexible sigmoidoscopy screening , 194,726 ( 55 % ) responded positively , and 170,432 eligible individuals were r and omised .  Attendance among those assigned screening was 71 % ( 40,674 of 57,254 ) . 2131 ( 5 % ) were classified as high-risk and referred for colonoscopy ; 38,525 with no polyps or only low-risk polyps detected were discharged . Distal adenomas were detected in 4931 ( 12.1 % ) and distal cancer in 131 ( 0.3 % ) . Proximal adenomas were detected in 386 ( 18.8 % of those undergoing colonoscopy ) and proximal cancer in nine cases ( 0.4 % ) . 62 % of cancers were Dukes ' stage A or locally excised . There was one perforation after flexible sigmoidoscopy and four after colonoscopy . An average of 48 people were screened , and two or three colonoscopy referrals generated , per centre each week . Interpretation Our flexible sigmoidoscopy screening regimen is acceptable , feasible , and safe . The prevalence of neoplasia is high , and colonoscopy referral rates of 5 % are acceptable BACKGROUND There is growing evidence that faecal-occult-blood ( FOB ) screening may reduce colorectal cancer ( CRC ) mortality , but this reduction in CRC mortality has not been shown in an unselected population -based r and omised controlled trial . The aim of this study was to assess the effect of FOB screening on CRC mortality in such a setting . METHODS Between February , 1981 , and January , 1991 , 152,850 people aged 45 - 74 years who lived in the Nottingham area of the UK were recruited to our study . Participants were r and omly allocated FOB screening ( 76,466 ) or no screening ( controls ; 76,384 ) . Controls were not told about the study and received no intervention . Screening-group participants were sent a Haemoccult FOB test kit with instructions from their family doctor . FOB tests were not rehydrated and dietary restrictions were imposed only for retesting borderline results . Individuals with negative FOB tests at the first screening , together with those who tested positive but in whom no neoplasia was found on colonoscopy , were invited to take part in further screening every 2 years . Screening was stopped in February , 1995 , by which time screening-group participants had been offered FOB tests between three and six times . Screening-group participants who had a positive test were offered full colonoscopy . All participants were followed up until June , 1995 . The primary outcome measure was CRC mortality . FINDINGS Of the 152,850 individuals recruited to the study , 2599 could not be traced or had emigrated and were excluded from the analysis . Thus , there were 75,253 participants in the screening group and 74,998 controls . 44,838 ( 59.6 % ) screening-group participants completed at least one screening . 28,720 ( 38.2 % ) of these individuals completed all the FOB tests they were offered and 16,118 ( 21.4 % ) completed at least one screening but not all the tests they were offered . 30,415 ( 40.4 % ) did not complete any test . Of 893 cancers ( 20 % stage A ) diagnosed in  screening-group participants ( CRC incidence of 1.49 
    Output:
    
In individuals with a higher risk of CRC due to family history , there is a consensus that it is appropriate to offer screening colonoscopy at < 50 years .
Panelists deemed  screening colonoscopy  appropriate for younger patients , with shorter surveillance intervals , where family or personal risk of colorectal cancer is higher .
Despite the lack of evidence based on r and omized controlled trials ( RCTs ) , colonoscopy is recommended by most published guidelines and EPAGE II criteria available online ( http://www.epage.ch ) , as a screening option for CRC in individuals at average risk of CRC , and undisputedly as the main screening tool for CRC in individuals at moderate and high risk of CRC