title: Relationship between number of breast cancer operations performed and 5-year survival after treatment for early-stage breast cancer.
abstract: OBJECTIVE
  We examined the association between number of breast cancer operations performed in a hospital (hospital volume) and all-cause and breast cancer-specific mortality using a national database and statistical methods appropriate for clustering and reducing confounding.
  
  
  METHODS
  In a retrospective cohort study, we linked Surveillance, Epidemiology, and End Results tumor registry data with Medicare claims data. The cohort included 11225 Medicare patients who had undergone surgery for early-stage breast cancer from 1994 to 1996 in 457 different hospitals. Primary outcomes were all-cause and breast cancer-specific survival rates at a mean follow-up time of 62.5 months.
  
  
  RESULTS
  In comparison with treatment in a low-volume hospital, treatment in a high-volume hospital was associated with hazard ratios of 0.83 (95% confidence interval [CI]=0.75, 0.92) for all-cause mortality and 0.80 (CI=0.66, 0.97) for breast cancer-specific mortality.
  
  
  CONCLUSIONS
  An association between the volume of breast cancer operations performed in a hospital and 5-year survival rates was observed for both all-cause and breast cancer-specific mortality. Further work investigating the aspects of hospital volume that contribute to increased survival is warranted.
authors.affiliation: Department of Medicine and Health Policy Institute, Medical College of Wisconsin, Milwaukee 53226, USA. gilligan@mcw.edu
authors.forename: Mary Ann
authors.initials: MA
authors.lastname: Gilligan
authors.forename: Joan
authors.initials: J
authors.lastname: Neuner
authors.forename: Xu
authors.initials: X
authors.lastname: Zhang
authors.forename: Rodney
authors.initials: R
authors.lastname: Sparapani
authors.forename: Purushottam W
authors.initials: PW
authors.lastname: Laud
authors.forename: Ann B
authors.initials: AB
authors.lastname: Nattinger
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D001943:Breast Neoplasms / Q000175:diagnosis / Q000401:mortality* / Q000601:surgery*; D002423:Cause of Death; D016000:Cluster Analysis; D005260:Female; D006801:Humans; D008408:Mastectomy / Q000706:statistics & numerical data; D015412:Mastectomy, Segmental / Q000706:statistics & numerical data; D006278:Medicare / Q000706:statistics & numerical data; D009367:Neoplasm Staging; D016016:Proportional Hazards Models; D018570:Risk Assessment; D018426:SEER Program; D013503:Surgery Department, Hospital / Q000592:standards* / Q000706:statistics & numerical data*; D016019:Survival Analysis; D014481:United States / Q000453:epidemiology