title: High-volume versus low-volume for esophageal resections for cancer: the essential role of case-mix adjustments based on clinical data.
abstract: BACKGROUND
  Most studies addressing the volume-outcome relationship in complex surgical procedures use hospital mortality as the sole outcome measure and are rarely based on detailed clinical data. The lack of reliable information about comorbidities and tumor stages makes the conclusions of these studies debatable. The purpose of this study was to compare outcomes for esophageal resections for cancer in low- versus high-volume hospitals, using an extensive set of variables concerning case-mix and outcome measures, including long-term survival.
  
  
  METHODS
  Clinical data, from 903 esophageal resections performed between January 1990 and December 1999, were retrieved from the original patients' files. Three hundred and forty-two patients were operated on in 11 low-volume hospitals (<7 resections/year) and 561 in a single high-volume center.
  
  
  RESULTS
  Mortality and morbidity rates were significantly lower in the high-volume center, which had an in-hospital mortality of 5 vs 13% (P < .001). On multivariate analysis, hospital volume, but also the presence of comorbidity proved to be strong prognostic factors predicting in-hospital mortality (ORs 3.05 and 2.34). For stage I and II disease, there was a significantly better 5-year survival in the high-volume center. (P = .04).
  
  
  CONCLUSIONS
  Hospital volume and comorbidity patterns are important determinants of outcome in esophageal cancer surgery. Strong clinical endpoints such as in-hospital mortality and survival can be used as performance indicators, only if they are joined by reliable case-mix information.
authors.affiliation: Surgical Oncology, Leiden University Medical Center, Leiden, The Netherlands. M.W.J.M.Wouters@lumc.nl
authors.forename: Michael W
authors.initials: MW
authors.lastname: Wouters
authors.forename: Bas P
authors.initials: BP
authors.lastname: Wijnhoven
authors.forename: Henrieke E
authors.initials: HE
authors.lastname: Karim-Kos
authors.forename: Harriet G
authors.initials: HG
authors.lastname: Blaauwgeers
authors.forename: Laurents P
authors.initials: LP
authors.lastname: Stassen
authors.forename: Willem-Hans
authors.initials: WH
authors.lastname: Steup
authors.forename: Huug W
authors.initials: HW
authors.lastname: Tilanus
authors.forename: Rob A
authors.initials: RA
authors.lastname: Tollenaar
mesh_terms: D000230:Adenocarcinoma / Q000401:mortality / Q000601:surgery; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D002294:Carcinoma, Squamous Cell / Q000401:mortality / Q000601:surgery; D004938:Esophageal Neoplasms / Q000401:mortality* / Q000601:surgery*; D016629:Esophagectomy / Q000706:statistics & numerical data*; D005260:Female; D017052:Hospital Mortality; D006761:Hospitals / Q000706:statistics & numerical data*; D006801:Humans; D007902:Length of Stay; D008297:Male; D008875:Middle Aged; D017063:Outcome Assessment, Health Care; D019984:Quality Indicators, Health Care; D012189:Retrospective Studies; D020379:Risk Adjustment; D015996:Survival Rate; D013997:Time Factors; D016896:Treatment Outcome