title: Breast cancer biology and ethnic disparities in breast cancer mortality in new zealand: a cohort study.
abstract: BACKGROUND
  Indigenous Māori women have a 60% higher breast cancer mortality rate compared with European women in New Zealand. We investigated differences in cancer biological characteristics and their impact on breast cancer mortality disparity between Māori and NZ European women.
  
  
  METHODS
  Data on 2849 women with primary invasive breast cancers diagnosed between 1999 and 2012 were extracted from the Waikato Breast Cancer Register. Differences in distribution of cancer biological characteristics between Māori and NZ European women were explored adjusting for age and socioeconomic deprivation in logistic regression models. Impacts of socioeconomic deprivation, stage and cancer biological characteristics on breast cancer mortality disparity between Māori and NZ European women were explored in Cox regression models.
  
  
  RESULTS
  Compared with NZ European women (n=2304), Māori women (n=429) had significantly higher rates of advanced and higher grade cancers. Māori women also had non-significantly higher rates of ER/PR negative and HER-2 positive breast cancers. Higher odds of advanced stage and higher grade remained significant for Māori after adjusting for age and deprivation. Māori women had almost a 100% higher age and deprivation adjusted breast cancer mortality hazard compared with NZ European women (HR=1.98, 1.55-2.54). Advanced stage and lower proportion of screen detected cancer in Māori explained a greater portion of the excess breast cancer mortality (HR reduction from 1.98 to 1.38), while the additional contribution through biological differences were minimal (HR reduction from 1.38 to 1.35).
  
  
  CONCLUSIONS
  More advanced cancer stage at diagnosis has the greatest impact while differences in biological characteristics appear to be a minor contributor for inequities in breast cancer mortality between Māori and NZ European women. Strategies aimed at reducing breast cancer mortality in Māori should focus on earlier diagnosis, which will likely have a greater impact on reducing breast cancer mortality inequity between Māori and NZ European women.
authors: Waikato Clinical School, University of Auckland, Hamilton, New Zealand.
authors: Sanjeewa
authors: S
authors: Seneviratne
authors: Waikato Clinical School, University of Auckland, Hamilton, New Zealand.
authors: Ross
authors: R
authors: Lawrenson
authors: Māori Health Services, Waikato District Health Board, Hamilton, New Zealand.
authors: Nina
authors: N
authors: Scott
authors: Waikato Breast Cancer Trust, Waikato Hospital, Hamilton, New Zealand.
authors: Boa
authors: B
authors: Kim
authors: Waikato Breast Cancer Trust, Waikato Hospital, Hamilton, New Zealand.
authors: Rachel
authors: R
authors: Shirley
authors: Waikato Clinical School, University of Auckland, Hamilton, New Zealand.
authors: Ian
authors: I
authors: Campbell
mesh_terms: D014408:Biomarkers, Tumor / Q000378:metabolism; D001943:Breast Neoplasms / Q000453:epidemiology / Q000378:metabolism / Q000401:mortality* / Q000473:pathology; D018270:Carcinoma, Ductal, Breast / Q000453:epidemiology / Q000378:metabolism / Q000401:mortality* / Q000473:pathology; D018275:Carcinoma, Lobular / Q000453:epidemiology / Q000378:metabolism / Q000401:mortality* / Q000473:pathology; D015331:Cohort Studies; D055088:Early Detection of Cancer; D005006:Ethnicity / Q000706:statistics & numerical data*; D005260:Female; D054625:Healthcare Disparities; D006801:Humans; D007124:Immunoenzyme Techniques; D008875:Middle Aged; D060787:Neoplasm Grading; D009361:Neoplasm Invasiveness; D009367:Neoplasm Staging; D009520:New Zealand / Q000453:epidemiology; D011379:Prognosis; D018719:Erb-b2 Receptor Tyrosine Kinases / Q000378:metabolism; D011960:Receptors, Estrogen / Q000378:metabolism; D011980:Receptors, Progesterone / Q000378:metabolism; D012042:Registries; D012307:Risk Factors; D015996:Survival Rate
chemical_list: D014408:Biomarkers, Tumor; D018719:Erb-b2 Receptor Tyrosine Kinases; D011960:Receptors, Estrogen; D011980:Receptors, Progesterone; C508053:ERBB2 protein, human