title: Switching between endocrine therapies for primary breast cancer: Frequency and timing in Australian clinical practice.
abstract: OBJECTIVE
  To determine the frequency, timing and patterns of endocrine therapy switching in Australian practice for postmenopausal women with primary breast cancer.
  
  
  METHODS
  We identified postmenopausal women in a population-based cohort commencing endocrine therapy for invasive primary breast cancer between December 2005 and December 2008 (n = 645). Individual-level administrative health records and self-report data were used to determine women's demographic and clinical characteristics, including preexisting and newly-treated comorbidities, and switches in endocrine therapy. Time to therapy switching was calculated. Chi-square tests compared the characteristics of women who did and did not switch, and those switching within 2 years or after 2 years of commencing therapy.
  
  
  RESULTS
  Twenty-eight percent of women switched from their initial endocrine therapy, most commonly from tamoxifen to anastrozole, or the converse. A small number of anastrozole-to-exemestane and letrozole-to-exemestane switches were observed (n = 19). Most women (>80%) who switched therapies did not have newly-treated comorbidities. Few women (<5%) switched before completing 2 years of therapy, but these women were significantly more likely to have preexisting antidepressant use than women switching later (43% vs 23%, P = 0.048) and remained on the subsequent therapy for less time (6 months vs 2.7 years, P < 0.001).
  
  
  CONCLUSIONS
  Approximately one-quarter of postmenopausal women with primary breast cancer switched endocrine therapies. The findings suggest that the majority of switching in Australian practice was planned; occurring after 2-3 years of, not precipitated by comorbidity, and in a sequence supported by trial evidence. Early switching, however, was associated with preexisting depression and appeared to be a marker of poor persistence.
authors.affiliation: University of Western Australia, 35 Stirling Hwy, Crawley, WA, 6009, Australia.|Quality Use of Medicines and Pharmacy Research Centre, School of Pharmacy and Medical Sciences, University of South Australia, GPO Box 2471, Adelaide, SA, 5001, Australia.
authors.forename: Anna
authors.initials: A
authors.lastname: Kemp-Casey
authors.affiliation: Quality Use of Medicines and Pharmacy Research Centre, School of Pharmacy and Medical Sciences, University of South Australia, GPO Box 2471, Adelaide, SA, 5001, Australia.
authors.forename: Elizabeth E
authors.initials: EE
authors.lastname: Roughead
authors.affiliation: University of Western Australia, 35 Stirling Hwy, Crawley, WA, 6009, Australia.
authors.forename: Christobel
authors.initials: C
authors.lastname: Saunders
authors.affiliation: Patricia Richie Centre for Cancer Care and Research, The Mater Hospital and University of Sydney, Rocklands Road, Sydney, NSW, 2060, Australia.
authors.forename: Frances
authors.initials: F
authors.lastname: Boyle
authors.affiliation: Institute of Health Research, University of Notre Dame, PO Box 1225, Fremantle, WA, 6959, Australia.
authors.forename: Max
authors.initials: M
authors.lastname: Bulsara
authors.affiliation: University of Western Australia, 35 Stirling Hwy, Crawley, WA, 6009, Australia.
authors.forename: David B
authors.initials: DB
authors.lastname: Preen
mesh_terms: D018931:Antineoplastic Agents, Hormonal / Q000008:administration & dosage / Q000627:therapeutic use*; D001315:Australia; D001943:Breast Neoplasms / Q000188:drug therapy*; D017024:Chemotherapy, Adjuvant; D015331:Cohort Studies; D005260:Female; D006801:Humans; D008875:Middle Aged
chemical_list: D018931:Antineoplastic Agents, Hormonal
keywords: 45 and Up Study; breast cancer; clinical guidelines; clinical practice; duration of therapy; endocrine therapy; switch