title: Survival after breast cancer treatment: the impact of provider volume.
abstract: BACKGROUND
  Research has not paid sufficient attention to the need for adequate case-mix adjustment in studies of the relationship between provider volume and performance. This study attempted to address this limitation by capturing and including 5-year survival outcomes and a wide range of case-mix variables in multivariate analyses of the volume-outcome relationship relating to breast cancer treatments.
  
  
  METHODS
  All patients diagnosed with invasive primary breast cancer during 1996 (n = 809) were included. Patient, disease and treatment data were extracted from medical records; survival data were corroborated using official death registrations. A Cox proportional hazards approach was used to model relationships between patient, disease and service variables and risk of death.
  
  
  RESULTS
  There were 262 deaths among 807 patients followed up; overall 5-year survival was 70%. Advancing age, higher levels of co-morbidity, late-stage disease, more positive nodes, and high-grade tumour were independently associated with lower survival (P < 0.05). Patients who received hormonal therapy (HR 0.50, 95% CI 0.28-0.89) and radiotherapy (HR 0.73, 95% CI 0.53-1.03) had a survival advantage. Using a cut-off point of > or =30 cases per annum, survival was lower for patients treated in low volume settings (HR 1.47, 95% CI 1.09-1.96) after adjustment for case mix.
  
  
  CONCLUSIONS
  There was some evidence to support treatment in high volume settings although patient and disease variables were the major determinants of survival for patients with breast cancer.
authors.affiliation: Clinical Research Support Centre, Education & Research Centre, Royal Hospitals, Belfast, Northern Ireland, UK. karen.bailie@crsc.n-i.nhs.uk
authors.forename: Karen
authors.initials: K
authors.lastname: Bailie
authors.forename: Iain
authors.initials: I
authors.lastname: Dobie
authors.forename: Stephen
authors.initials: S
authors.lastname: Kirk
authors.forename: Michael
authors.initials: M
authors.lastname: Donnelly
mesh_terms: D000367:Age Factors; D000368:Aged; D000369:Aged, 80 and over; D018931:Antineoplastic Agents, Hormonal / Q000627:therapeutic use; D001943:Breast Neoplasms / Q000401:mortality* / Q000473:pathology / Q000628:therapy*; D003131:Combined Modality Therapy; D005260:Female; D006801:Humans; D008593:Menopause / Q000502:physiology; D008875:Middle Aged; D010818:Practice Patterns, Physicians' / Q000706:statistics & numerical data*; D016016:Proportional Hazards Models; D020379:Risk Adjustment; D012720:Severity of Illness Index; D012959:Socioeconomic Factors; D015996:Survival Rate