title: A competing risk analysis of hormone therapy interruption in Asian women with breast cancer.
abstract: OBJECTIVE
  This study aimed to use a competing risk approach to evaluate the probability of the occurrence of hormone therapy (HT) interruption and to assess its associated predictors in Asian women with breast cancer.
  
  
  METHODS
  This retrospective cohort study used the Taiwan Health Insurance Research Database from 2003 to 2011. Reimbursement data for women with newly diagnosed primary breast cancer were extracted. Interruption (gap ≥ 180 days) and time to first interruption of HT were identified. The probability of interruption was analysed by Kaplan-Meier (KM) method and cumulative incidence competing risk (CICR) method. Competing risk regressions were used to assess the predictors of interruption.
  
  
  RESULTS
  The 5-year cumulative incidence of first HT interruption was 14% versus 13% estimated by the KM and the CICR methods, respectively. The estimated incidences from CICR method tended to be around 11% lower than KM method in various HT utilization patterns. Younger (≤50 years) age at diagnosis, switching HT and the presence of HT-related adverse events were identified as predictors of interruption in competing risk regressions.
  
  
  CONCLUSIONS
  The competing risk approach provided lower probabilities and estimates when investigating the incidence of first interruption than the standard survival analysis. The competing risk method, which takes into account the competing risks from cancer recurrence and death, should be considered in future analysis. In terms of improving persistence of HT, it is important to focus on patients of younger age at diagnosis, HT switching and experiencing adverse events.
authors.affiliation: School of Pharmacy, College of Pharmacy, Kaohsiung Medical University, Kaohsiung, Taiwan; Department of Pharmacy, Kaohsiung Medical University Hospital, Kaohsiung, Taiwan.
authors.forename: Kun-Pin
authors.initials: KP
authors.lastname: Hsieh
authors.forename: Li-Chia
authors.initials: LC
authors.lastname: Chen
authors.forename: Kwok-Leung
authors.initials: KL
authors.lastname: Cheung
authors.forename: Yi-Hsin
authors.initials: YH
authors.lastname: Yang
mesh_terms: D000368:Aged; D018931:Antineoplastic Agents, Hormonal / Q000008:administration & dosage*; D047072:Aromatase Inhibitors / Q000008:administration & dosage*; D044466:Asian People; D001943:Breast Neoplasms / Q000175:diagnosis / Q000188:drug therapy* / Q000453:epidemiology*; D015331:Cohort Studies; D004334:Drug Administration Schedule; D005260:Female; D006305:Health Status Indicators; D006801:Humans; D008875:Middle Aged; D012189:Retrospective Studies
chemical_list: D018931:Antineoplastic Agents, Hormonal; D047072:Aromatase Inhibitors
keywords: breast cancer; competing risks; drug utilization; hormone therapy; interruption; persistence; pharmacoepidemiology