title: Adherence to adjuvant endocrine therapy: is it a factor for ethnic differences in breast cancer outcomes in New Zealand?
abstract: OBJECTIVE
  Despite the benefits of adjuvant endocrine therapy for hormone receptor positive breast cancer, many women are non-adherent or discontinue endocrine treatment early. We studied differences in adherence to adjuvant endocrine therapy by ethnicity in a cohort of New Zealand women with breast cancer and its impact on breast cancer outcomes.
  
  
  METHODS
  We analysed data on women (n = 1149) with newly diagnosed hormone receptor positive, non-metastatic, invasive breast cancer who were treated with adjuvant endocrine therapy in the Waikato during 2005-2011. Linked data from the Waikato Breast Cancer Registry and National Pharmaceutical Database were examined to identify differences by ethnicity in adherence to adjuvant endocrine therapy and the effect of sub-optimal adherence on cancer recurrence and mortality.
  
  
  RESULTS
  Overall, a high level of adherence of ≥80% was observed among 70.4% of women, which declined from 76.8% to 59.3% from the first to fifth year of treatment. Māori women were significantly more likely to be sub-optimally adherent (<80%) compared with European women (crude rate 37% vs. 28%, p = 0.005, adjusted OR = 1.51, 95% CI 1.04-2.17). Sub-optimal adherence was associated with a significantly higher risk of breast cancer mortality (HR = 1.77, 95% CI 1.05-2.99) and recurrence (HR = 2.14, 95% CI 1.46-3.14).
  
  
  CONCLUSIONS
  Sub-optimal adherence to adjuvant endocrine therapy was a likely contributor for breast cancer mortality inequity between Māori and European women, and highlights the need for future research to identify effective ways to increase adherence in Māori women.
authors.affiliation: Waikato Clinical School, University of Auckland, New Zealand. Electronic address: Sanjeewa.Seneviratne@waikatodhb.health.nz.
authors.forename: Sanjeewa
authors.initials: S
authors.lastname: Seneviratne
authors.affiliation: Waikato Clinical School, University of Auckland, New Zealand.
authors.forename: Ian
authors.initials: I
authors.lastname: Campbell
authors.affiliation: Māori Health Services, Waikato District Health Board, Hamilton, New Zealand.
authors.forename: Nina
authors.initials: N
authors.lastname: Scott
authors.affiliation: Department of Oncology, Waikato District Health Board, Hamilton, New Zealand.
authors.forename: Marion
authors.initials: M
authors.lastname: Kuper-Hommel
authors.affiliation: Waikato Breast Cancer Trust, Waikato Hospital, Hamilton, New Zealand.
authors.forename: Boa
authors.initials: B
authors.lastname: Kim
authors.affiliation: Department of Statistics, University of Auckland, New Zealand.
authors.forename: Avinesh
authors.initials: A
authors.lastname: Pillai
authors.affiliation: Waikato Clinical School, University of Auckland, New Zealand.
authors.forename: Ross
authors.initials: R
authors.lastname: Lawrenson
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D018931:Antineoplastic Agents, Hormonal / Q000627:therapeutic use*; D047072:Aromatase Inhibitors / Q000627:therapeutic use*; D001943:Breast Neoplasms / Q000737:chemistry / Q000188:drug therapy* / Q000208:ethnology / Q000401:mortality*; D017024:Chemotherapy, Adjuvant; D005260:Female; D006801:Humans; D053208:Kaplan-Meier Estimate; D008207:Lymphatic Metastasis; D008875:Middle Aged; D009364:Neoplasm Recurrence, Local / Q000188:drug therapy*; D009520:New Zealand / Q000208:ethnology; D010349:Patient Compliance / Q000208:ethnology*; D011446:Prospective Studies; D012042:Registries; D013629:Tamoxifen / Q000627:therapeutic use; D016896:Treatment Outcome; D044465:White People / Q000706:statistics & numerical data
chemical_list: D018931:Antineoplastic Agents, Hormonal; D047072:Aromatase Inhibitors; D013629:Tamoxifen
keywords: Breast cancer; Endocrine therapy; Ethnicity; Inequity; Medication adherence