***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: Objective : This study was performed to identify tumor- and patient-related risk factors for distal rectal cancer in patients treated with an abdominoperineal resection ( APR ) associated with positive circumferential resection margin ( CRM ) , local recurrence ( LR ) , and overall survival ( OS ) . Background : The introduction of total mesorectal excision ( TME ) has improved the outcome of patients with rectal cancer . However , survival of patients treated with an APR improved less than of those treated with low anterior resections ( LAR ) . Besides , an APR is associated with a higher LR rate . Methods : Patients were selected from the TME trial , which is a r and omized , multicenter trial , study ing the effects of preoperative radiotherapy ( RT ) in 1861 patients . Of the Dutch patients , 455 underwent an APR .  Location of the bulk of the tumor was scored with surgery , pathology , or other reports . CRM was available from pathology reports . Result : A positive CRM was found in 29.6 % of all patients , 44 % for anterior , 21 % for lateral , 23 % for posterior , and 17 % for (semi)circular tumor location ( P < 0.0001 ) . In a multivariate analysis , T-stage , N-stage , and tumor location were independent risk factors for CRM . If a ( partial ) resection of the vaginal wall was performed in women , 47.8 % of patients still had a positive CRM . T-stage , N-stage , and CRM were risk factors for LR and age , T-stage , N-stage , CRM , and distance of the inferior tumor margin to the anal verge for OS . Conclusion : Age , T-stage , N-stage , CRM , distance of the tumor to the anal verge , and tumor location were independent risk factors for adverse outcome in patients treated with an APR for low rectal cancer . Anterior location , specifically in women , more often requires downstaging and /or more extended resection to obtain free margins PURPOSE : This study was design ed to examine the outcome of cancer of the lower rectum , particularly the rates of local recurrence and survival for tumors located in this area that have been treated by anterior or abdominoperineal resections . METHODS : A prospect i ve , observational , national , cohort study which is part of the Norwegian Rectal Cancer Project . The present cohort includes all patients undergoing total mesorectal excision in 47 hospitals during the period November 1993 to December 1999 . A total of 2,136 patients with rectal cancer within 12 cm of the anal verge were analyzed ; there were 1,315 ( 62 percent ) anterior resections and 821 ( 38 percent ) abdominoperineal resections . The lower edge of the tumor was located 0 to 5 cm from the anal verge in 791 patients , 6 to 8 cm in 558 patients , and 9 to 12 cm in 787 patients . According to the TNM classification , there were 33 percent Stage I , 35 percent Stage II , and 32 percent Stage III . RESULTS : Univariate analyses : The five-year local recurrence rate was 15 percent in the lower level , 13 percent in the intermediate level , and 9 percent in the upper level ( P = 0.014 ) . It was 10 percent local recurrence after anterior resection and 15 percent after abdominoperineal resection ( P = 0.008 ) . The five-year survival rate was 59 percent in the lower level , 62 percent in the intermediate level , and 69 percent in the upper level ( P < 0.001 ) , respectively , and it was 68 percent in the anterior-resection group and 55 percent in the abdominoperineal-resection group ( P < 0.001 ) . Multivariate analyses : The level of the tumor influenced the risk of local recurrence ( hazard ratio , 1.8 ; 95 percent confidence interval , 1.1–2.3 ) , but the operative procedure , anterior resection vs. abdominoperineal resection , did not ( hazard ratio , 1.2 ; 95 percent confidence interval , 0.7–1.8 ) . On the contrary , operative procedure influenced survival ( hazard ratio , 1.3 ; 95 percent confidence interval , 1–1.6 ) , but tumor level did not ( hazard ratio , 1.1 ; 95 percent confidence interval , 0.9–1.5 ) . In addition to patient and tumor characteristics ( T4 tumors ) , intraoperative bowel perforation and tumor involvement of the circumferential margin were identified as significant prognostic factors , which were more common in the lower rectum , explaining the inferior prognosis for tumors in this region . CONCLUSIONS : T4 tumors , R1 resections , and /or intraoperative perforation of the tumor or bowel wall are main features of low rectal cancers , causing inferior oncologic outcomes for tumors in this area . If surgery is optimized , preventing intraoperative perforation and involvement of the circumferential resection margin , the prognosis for cancers of the lower rectum seems not to be inherently different from that for tumors at higher levels . In that case , the level of the tumor or the type of resection will not be indicators for selecting patients for radiotherapy Aim Conventional outcomes such as survival , tumour recurrence and complication rates after surgery for rectal cancer have been rigorously assessed , but the importance of maintaining quality of life ( QOL ) after surgery for rectal cancer has received less attention . The aim of the current study was to analyse QOL and the occurrence of pelvic dysfunction after the surgical treatment of rectal cancer BACKGROUND Minimum numbers of cases required for certification by the American Board of Colon and Rectal Surgery ( ABCRS ) have been determined from a prospect i ve data base of all applicants applying for examination since 1989 . These data represent the longitudinal evolution of practice patterns in tertiary colorectal training programs . STUDY DESIGN After obtaining permission from the ABCRS , access to the data base was obtained and data from the 12-year period 1994 to 2005 were analyzed . RESULTS The data base contains the operative and endoscopic case numbers of 673 residents . The number of training programs increased from 28 to 39 ( 28 % ) and the number of residency positions from 50 to 66 ( 24 % ) . Median numbers of anorectal patients per resident remained remarkably constant over the period of study . Both  rigid sigmoidoscopy  ( 67 to 44 per resident ) and  flexible sigmoidoscopy  ( 135.5 to 39 per resident ) decreased substantially ; colonoscopy volume increased ( 209 to 264 per resident ) . Perineal procedures for rectal prolapse consistently comprise 50 % to 60 % of the total procedures for prolapse . Low anterior resection for rectal cancer outnumber abdominoperineal resections by a 3/1 ratio . Coloanal anastomoses have steadily increased . Laparoscopic approaches for all abdominal operations have increased substantially , with the greatest increase being in diverticular resections ( 6.5 % to 44.7 % ) . CONCLUSIONS Prospect i ve data collection by ABCRS has permitted calculation of minimum numbers of operative cases for training colorectal surgeons , with the advantage of a rolling average that reflects evolving practice patterns in teaching programs . Analysis of these data allows planning of needs-based educational programs and may ultimately be involved in design ing the maintenance of certification process Purpose Local recurrence and cure rates following abdominoperineal resections have been reported to be much worse than sphincter-preserving anterior resections . We compared the oncologic outcomes of patients treated by abdominoperineal resections with those following sphincter-preserving anterior resections . Methods The medical records of patients who underwent radical rectal resection for rectal carcinoma at the Colorectal Surgery Department , Singapore General Hospital , during the period from April 1989 to April 2002 were review ed . A total of 791 cases were studied . Operative procedures were classified as either abdominoperineal resections or anterior resections with either straight or pouch anastomosis . Total mesorectal excision was routinely performed for carcinomas of the lower middle and lower third of the rectum . Sentinel events , including local and systemic recurrences or morbidity and mortality , were tracked prospect ively . Results There were a total of 93 abdominoperineal resections ( 12.1 percent ) , 547 anterior resections with straight anastomoses ( 71 percent ) , and 130 anterior resections with pouch anastomoses ( 16.9 percent ) . Postoperative mortality was 2.6 percent and postoperative morbidity was 13.6 percent with an overall anastomotic leakage rate of 2.5 percent . The cumulative five-year local recurrence rate was 5.4 percent for abdominoperineal resections , 3.6 percent for anterior resections with straight anastomoses , and 3.8 percent for anterior resections with pouch anastomoses ( P = 0.73 by log-rank test ) . The median time to local recurrence also did not differ significantly between the different procedures ( abdominoperineal resections , 17 months , anterior resections with straight anastomoses , 18 months , anterior resections with pouch anastomoses , 13 months ) . Independent predictors for local recurrence included advanced tumor stage , tumor depth , and poorly differentiated tumors . The five-year cancer-specific survival was 70 percent . The type of anastomosis did not influence disease-free survival with median disease-free survival for patients who underwent abdominoperineal resections being 100 months , survival of anterior resections with straight anastomoses being 135 months , and survival of anterior resections with pouch anastomoses being 121 months ( P = 0.33 by log-rank test ) . The independent factors for poor survival were age greater than 65 years , advanced tumor stage , tumor depth , and poorly differentiated tumors . Conclusion Both abdominoperineal resections and sphincter-preserving anterior resections can be performed safely with low morbidity and mortality in a specialized high-volume hospital unit without compromising oncologic outcomes . With appreciation of the anatomic relations in total mesorectal excision and st and ardized consistent surgical technique , the oncologic outcomes of patients treated by  abdominoperineal resections  are not worse than those treated by sphincter-preserving anterior resections PURPOSE Despite the major improvements that have been made due to total mesorectal excision ( TME ) , low rectal cancer still remains a challenge . METHODS By investigating a prospect i ve r and omized rectal cancer trial in which surgeons had undergone training in  TME  the factors responsible for the poor outcome were determined and a new method for assessing the quality of surgery was tested . RESULTS Survival differed greatly between abdominoperineal resection ( APR ) and anterior resection ( AR ; 38.5 % v 57.6 % , P = .008 ) . Low rectal carcinomas have a higher frequency of circumferential margin involvement ( 26.5 % v 12.6 % , P < .001 ) . More positive margins were present in the patients operated with APR ( 30.4 % ) compared to AR ( 10.7 % , P = .002 ) . Furthermore , more perforations were present in these specimens ( 13.7 % v 2.5 % , P < .001 ) . The plane of resection lies within the sphincteric muscle , the submucosa or lumen in more than 1/3 of the APR cases , and in the remainder lay on the sphincteric muscles . CONCLUSION We systematic ally described and investigated the pathologic properties of low rectal cancer in general , and APR in particular , in a prospect i ve r and omized trial including surgeons who had been trained in TME . The poor prognosis of the patients with an APR  is ascribed to the resection plane of the operation leading to a high frequency of margin involvement by tumor and perforation with this current surgical technique . The clinical results of this operation could be greatly improved by adopting different surgical techniques and possibly greater use of radiochemotherapy PURPOSE : Issues related to body image and a permanent stoma after abdominoperineal resection may decrease quality of life in rectal cancer patients . However , specific problems associated with a low anastomosis may similarly affect quality of life for patients undergoing low anterior resection .  The aim of this study was to compare quality of life of low rectal cancer patients after undergoing abdominoperineal resection versus low anterior resection .  METHODS : Demographics , tumor and treatment characteristics , and prospect ively collected preoperative quality -of-life data for patients undergoing low anterior resection or abdominoperineal resection for low rectal cancer between 1995 and 2009 were compared . Quality of life collected at specific time intervals was compared for the two groups , adjusting for age , body mass index , use of chemoradiation , and 30 days postoperative complications . The short-form-36 question naire was used to determine quality of life . RESULTS : The query returned 153 patients ( abdominoperineal resection = 68 , low anterior resection = 85 ) with a median follow-up of 24 ( 3 - 64 ) mo . The after abdominoperineal resection group had a higher mean age ( 63 ± 12 vs. 54 ± 12 , p < 0.001 ) and more American Society of Anesthesiologists classification 3/4 patients ( 65 percent vs. 43 percent , p = 0.03 ) than low anterior resection . Other demographics , tumor stage , use of chemoradiation , overall postoperative complication rates , and quality -of-life follow-up time were 
    Output:
    
Patients treated by APR  have a higher rate of CRM involvement , a higher local recurrence , and poorer prognosis than LAR .
And there is evidence that in selected low rectal cancer patients , LAR can be used safely with a better oncological outcome than APR .