***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 diagnosis of a lymph node-negative colorectal carcinoma should imply a good prognosis ; however , the outcomes for TNM stage II patients remain variable . Few studies have examined the relationship of the number of lymph nodes examined to the prognosis of this stage . The aim of this study was to determine whether the number of lymph nodes examined has an effect on prognosis of a relatively large sample of patients undergoing curative surgery for stage II colorectal cancer at a single institution . Data on patients who underwent surgery for colorectal cancer between January 1980 and April 2000 were prospect ively collected in a data base . Patients with TNM stage II or stage III tumours who were treated with curative intent were removed . Patients over 80 years of age were excluded from the survival analysis .  Survival comparisons were made using Kaplan-Meier curves and the log-rank test . Multivariate analysis was performed using a Cox regression model . A total of 625 cases of TNM stage II cases and , for comparison purpose s , 415 stage III cases , were analysed .  Lymph node retrieval in stage II cases was affected by the patient 's age ( P=0.04 ) and gender ( P=0.02 ) , tumour grade ( P<0.0001 ) , tumour site ( P<0.0001 ) , and necessity to carry out extended resection ( P<0.0001 ) . In stage III cases , lymph node retrieval was affected by patient age ( P<0.0001 ) , tumour grade ( P=0.02 ) , and tumour site ( P=0.002 ) . Decreased lymph node detection was associated with increasing hazard ratios among the 480 TNM stage II patients under 80 years of age , but not among the 345 patients with TNM stage III tumours .  Five year survival rate for patients with stage III tumours with only 1 - 3 positive lymph nodes ( 52.6 % ) was similar to that of patients with stage II tumour who had nine or fewer lymph nodes examined ( 51.3 % ) . These results demonstrate that the prognosis of TNM stage II colorectal cancer is dependent on the number of lymph nodes examined . Patients with few nodes examined have a poorer prognosis . It is possible that a smaller number of lymph nodes examined reflects a diminished immune response . It can be presumed that those patients with stage II tumour with only a few nodes examined should be offered postoperative chemotherapy on a routine basis The purpose of tumour staging for colorectal cancer ( CRC ) is to help define clinical management , facilitate communication between physicians , provide a basis for stratification and analysis of treatment results in prospect i ve studies , and provide some prognostic information for patients and their families . The World Congresses of Gastroenterology , Digestive Endoscopy , and Coloproctology , Working Party on staging for CRC studied six commonly used systems to review their strengths and weaknesses . Although it was concluded that defining a new staging system was unnecessary , it was recognized that there is a need to define a terminology to describe the full anatomic extent of spread of CRC . Furthermore , we note that there are several additional features , derived from both clinical and pathology information , which have had prognostic significance shown by appropriately constructed multivariate analyses and which can be used to formulate a more accurate prognostic index than that provided by a description of anatomical tumour spread . Thus the Working Party came to two principal conclusions . First , a st and ard format should be adopted for the collection of the essential data required for prospect i ve studies , and we recommend the ' International Documentation System ( IDS ) for CRC ' for this purpose . Second , a nomenclature which describes the full anatomical extent of tumour spread and residual tumour status in CRC has been defined and should be adopted , from which all currently used staging systems can be derived . We have called this nomenclature the '  International Comprehensive Anatomical Terminology  ( ICAT ) for CRC ' . In the event that these recommendations are adopted , we envision that there will be improved clarity in the documentation of treatment outcome for patients with CRC and improved communication of results derived from prospect i ve studies . Furthermore , an acceptance of IDS and ICAT would set the scene to develop a prognostic index for individual patients with CRC by the expansion of anatomical clinicopathology staging information to include additional factors which have independent prognostic significance Abstract Background : T3N0 colon cancer is the target of many adjuvant studies . Very few studies have examined the relationship of the number of lymph nodes examined to the prognosis of this stage . We examined data from the National Cancer Data Base ( NCDB ) to determine whether the number of examined lymph nodes is prognostic for T3N0 colon cancer . Methods : A total of 35,787 prospect ively collected cases of T3N0 colon cancer that were surgically treated and pathologically reported from 1985 to 1991 to the NCDB as T3N0M0 were analyzed . Results : The 5-year relative survival rate for T3N0M0 colon cancer varied from 64 % if 1 or 2 lymph nodes were examined to 86 % if > 25 lymph nodes were examined . Three strata of lymph nodes ( 1–7 , 8–12 , and ≥13 ) distinguished significantly different observed 5-year survival rates . Conclusions : These results demonstrate that the prognosis of T3N0 colon cancer is dependent on the number of lymph nodes examined . A minimum of 13 lymph nodes should be examined to label a T3 colon cancer as node negative . These data suggest that adjuvant trials for T3N0 colon cancer should stratify according to the number of lymph nodes examined PURPOSE : This study was developed to compare median and actuarial survival after left hemicolectomyvs.left segmental colectomy . METHODS : Between January 1980 and January 1985 , 270 consecutive patients ( 133 males and 137 females ; mean age , 64±12 ( range , 18–91 ) years with left colonic carcinoma located between the left third of the transverse colon and ( but not , including ) the colorectal juncture were r and omly allotted to undergo either left hemicolectomy or left segmental colectomy . Left hemicolectomy removed the entire left colon along with the origin of the inferior mesenteric artery and the dependent lymphatic territory . Left segmentai colectomy removed a more restricted segment of the colon and left the origin of the inferior mesenteric artery unmolested . RESULTS : After elimination of 10 patients for protocol violation , 131 patients with left hemicolectomy and 129 with left segmental colectomy were analyzed . Both groups were similar with regard to preoperative risk factors ( age , sex , obesity , weight loss , anemia , diabetes , cirrhosis , kidney failure , steroid therapy or radiation therapy performed for any cause other than cancer ) , pathology findings ( size , degree of differentiation , Dukes stage , invasion of lymph nodes at the origin of the inferior mesenteric artery ) , and associated lesions . Only the length of tumor-free margins of colon removed was significantly longer in left hemicolectomy . The number of early postoperative abdominal and extra-abdominal complications was similar in both groups . Overall , early postoperative mortality was 4 percent higher , but not significantly in left hemicolectomy ( eight deaths , 6 percent ) than in left segmental colectomy ( three deaths , 2 percent ) . Median survival was 10 years and nearly equivalent in both groups . The two actuarial survivai curves were similar . Bowel movement frequency was significantly increased after left hemicolectomy during the first postoperative year . Our results suggest that survival after left segmental colectomy is equivalent to that of left hemicolectomy . Notwithst and ing the observation of other carcinologic rules , left segmental colectomy rather than left hemicolectomy may theoretically be performed under laparoscopy without compromising the carcinologic outcome AIMS Population -based cancer registries can provide excellent data for insight in disease management practice . This study examines the extent to which the consensus-based national clinical guidelines ( version 2000 - 2001 ) for colorectal cancer ( CRC ) had been implemented in the diagnostic and treatment approach in the Southern Netherl and s in 2002 . METHODS Data were gathered from the medical records for a r and om sample from the Eindhoven Cancer Registry of 308 patients with colorectal cancer . Adherence to clinical guidelines was determined for diagnostic assessment , pathology , and treatment during the first year after diagnosis . RESULTS Surgical procedures and referral for pre-operative radiotherapy were carried out largely conform the recommendations . The number of performed colonoscopies  among colon cancer patients amounted to 60 % ; contrast enemas after incomplete colonoscopy  were performed in only 27 % of patients . The median number of examined lymph nodes was only six for patients with colon and five for patients with rectal cancer ; the administration of adjuvant chemotherapy  for patients with stage III colon cancer decreased from 95 % of patients younger than 70 years to 48 % of patients over 70 . CONCLUSIONS Adherence to clinical guidelines was not optimal . Feedback to surgeons and pathologists should improve adherence , especially with respect to nodal retrieval and assessment PURPOSE To determine the relationship , in patients with adenocarcinoma of the colon , between survival and the number of lymph nodes analyzed from surgical specimens . PATIENTS AND METHODS Intergroup Trial INT-0089 is a mature trial of adjuvant chemotherapy for high-risk patients with stage II and stage III colon cancer . We performed a secondary analysis of this group with overall survival ( OS ) as the main end point . Cause-specific survival ( CSS ) and disease-free survival were secondary end points . Rates for these outcome measures were estimated using Kaplan-Meier methodology . Log-rank test was used to compare overall curves , and Cox proportional hazards regression was used to multivariately assess predictors of outcome . RESULTS The median number of lymph nodes removed at colectomy was 11 ( range , one to 87 ) . Of the 3411 assessable patients , 648 had no evidence of lymph node metastasis . Multivariate analyses were performed on the node-positive and node-negative groups separately to ascertain the effect of lymph node removal . Survival decreased with increasing number of lymph node involvement ( P = .0001 for all three survival end points ) . After controlling for the number of nodes involved , survival increased as more nodes were analyzed ( P = .0001 for all three end points ) . Even when no nodes were involved , OS and CSS improved as more lymph nodes were analyzed ( P = .0005 and P = .007 , respectively ) . CONCLUSION The number of lymph nodes analyzed for staging colon cancers is , itself , a prognostic variable on outcome . The impact of this variable is such that it may be an important variable to include in evaluating future trials Context While studies suggest that surgical patients fare best with providers ( hospitals and surgeons ) that perform a high volume of procedures , most have not accounted for the tendency of patients of 1 provider to have similar outcomes ( clustering ) . When outcomes of individual patients are clustered , more patients are required to prove that providers ' outcomes differ from one another . Contribution This re analysis of data from 3 previously published volume outcome studies of surgery  accounted for clustering within provider . Statistical significance of volume outcome relationships of morbidity end points was attenuated substantially after adjustment for the effects of clustering . Implication s Planners considering regionalizing surgery should remember that volume outcome studies that have not accounted for clustering exaggerate differences in outcomes by provider . The Editors In an attempt to evaluate the degree to which the choice of provider affects outcomes of major medical procedures , numerous investigators have used procedure volume as a proxy for expertise and have conducted studies correlating volume with outcomes . However , volume is a crude , easily calculated measure , and its use may overlook large variations in quality among providers that are independent of the number of procedures performed . If there are such large variations in outcomes among providers , the outcomes of patients treated by the same provider are necessarily correlated , or clustered . Clustering of this nature invali date s conventional statistical analyses . Patients treated at the same hospital or by the same surgeon may be more likely to experience similar outcomes if surgical technique or supportive care practice s vary among providers and if these factors affect outcomes . It is well established that statistical methods must correct for the effect of clustering of this nature if it exists ( 1 - 3 ) . In general , correction for clustering attenuates the statistical significance of observed trends . In this article , we describe measures that characterize the degree of clustering of outcomes and methods that permit the calculation of tests of statistical significance that are adjusted for the impact of clustering . We reanalyzed 3 large studies of major cancer surgery ( 4 - 7 ) and found examples that illustrate varying degrees of clustering . This re analysis focused on the relationship of  surgeon volume to outcome . We explored the effect of correction for clustering on the statistical significance of tests for association between surgeon volume and outcome . Graphical methods that visually characterize the degree of between-surgeon variation in quality after adjustment for volume and case mix are described . We also explored analyses that attempt to distinguish between the effects of surgeon volume and those of hospital volume . Methods Data Sources All 3 data sets were obtained by using the linkage of the Surveillance , Epidemiology , and End Results registries with Medicare cl aims from the Centers for Medicare & Medicaid Services ( formerly Health Care Financing Administration ) ( 8) . These linkages permit evaluation of the outcomes of surgery for all patients who received a diagnosis of cancer in the geographical regions defined by the registries . Patients were enrolled in Part A and Part B Medicare but were not enrolled in a health maintenance organization , and each had a diagnosis of colon , prostate , or rectal cancer made at age 65 years or older in a region covered by one of the Surveillance , Epidemiology , and End Results registries . All tumors were primary 
    Output:
    
CONCLUSIONS The number of lymph nodes evaluated after surgical resection was positively associated with survival of patients with stage II and stage III colon cancer .