title: Breast cancer recurrence following active treatment: determining its incidence in the NSW population.
abstract: OBJECTIVE
  It is important for consumers, clinicians and health service planners to know the risk of recurrence of primary breast cancer after initial treatment. At present, none of Australia's state or territory cancer registries routinely report this information. We aimed to determine the incidence of recurrence in New South Wales (NSW) clinical practice for the period 18 months to 6 years after diagnosis of primary breast cancer.
  
  
  METHODS
  Retrospective cohort study using population-based linked health data.
  
  
  METHODS
  We identified 2416 women in the 45 and Up Study who were diagnosed with primary invasive breast cancer between 2003 and 2008 in NSW, and who had not had a recurrence 18 months after diagnosis. Unit-level hospital, pharmacy and outpatient medical claims were used to identify treatment for recurrence. Incidence of recurrence was calculated using individual person-time at risk (18 months to 6 years postdiagnosis), with follow-up censored for death or end of study period (median follow-up 3 years). Time to recurrence was calculated, and Cox proportional regression was used to identify women's baseline and active treatment characteristics that were predictive of recurrence up to 6 years postdiagnosis.
  
  
  RESULTS
  217 women (9%) had a hospital, pharmacy or outpatient claim indicating breast cancer recurrence. Overall annual incidence of recurrence was 3.3%. Recurrence rates were significantly higher for women with node-positive (4.8% vs 2.5% annually; hazard ratio [HR] = 1.7; 95% confidence interval [95% CI] 1.3, 2.3) or hormone receptor-negative tumours (3.8% vs 3.1% annually; HR = 1.3; 95% CI 1.0, 1.7). Women with tumours >2 cm at diagnosis were more likely to experience recurrence than women with smaller/unknown tumours (4.8% vs 2.7% annually; HR = 1.5; 95% CI 1.1, 2.0).
  
  
  CONCLUSIONS
  A combination of routinely collected administrative health datasets can be used to determine recurrence rates, allowing future assessment of population-level changes over time and investigations of the real-world impact of specific treatments on outcomes.
authors: Centre for Health Services Research, School of Population Health, The University of Western Australia, Perth; Quality Use of Medicines and Pharmacy Research Centre, School of Pharmacy and Medical Sciences, University of South Australia, Adelaide, anna.kemp@uwa.edu.au.
authors: Anna
authors: A
authors: Kemp-Casey
authors: Quality Use of Medicines and Pharmacy Research Centre, School of Pharmacy and Medical Sciences, University of South Australia, Adelaide.
authors: Elizabeth R
authors: ER
authors: Roughead
authors: School of Surgery, The University of Western Australia, Perth.
authors: Christobel
authors: C
authors: Saunders
authors: Patricia Richie Centre for Cancer Care and Research, The Mater Hospital and The University of Sydney, NSW, Australia.
authors: Frances
authors: F
authors: Boyle
authors: Centre for Health Services Research, School of Population Health, The University of Western Australia, Perth.
authors: Derrick
authors: D
authors: Lopez
authors: Institute for Health Research, University of Notre Dame, Fremantle, Western Australia.
authors: Max
authors: M
authors: Bulsara
authors: Centre for Health Services Research, School of Population Health, The University of Western Australia, Perth.
authors: David B
authors: DB
authors: Preen
mesh_terms: D001943:Breast Neoplasms / Q000453:epidemiology*; D016208:Databases, Factual; D005260:Female; D006801:Humans; D015994:Incidence; D009364:Neoplasm Recurrence, Local / Q000453:epidemiology*; D009517:New South Wales / Q000453:epidemiology; D016016:Proportional Hazards Models; D012189:Retrospective Studies