Purpose: We investigated the breast cancer survival disparity between Indigenous Māori and non-Indigenous European women in New Zealand, and quantified the relative contributions of patient, tumor and healthcare system factors toward this disparity.
Methods: All women diagnosed with breast cancer in Waikato, New Zealand, during 1999-2012 were identified from the Waikato Breast Cancer Register. Cancer-specific survivals were compared using Kaplan-Meier survival curves, while contributions of different factors toward the survival disparity were quantified with serial Cox proportional hazard modeling.
Results: Of the 2,679 women included in this study, 2,260 (84.4%) were NZ European and 419 (15.6%) were Māori. Compared with NZ European women, Māori women had a significantly higher age-adjusted cancer-specific mortality (HR 2.02, 95% CI 1.59-2.58) with significantly lower 5-year (86.8 vs. 76.1%, p < 0.001) and 10-year (79.9 vs. 66.9%, p < 0.001%) crude cancer-specific survivals. Stage at diagnosis made the greatest contribution (approximately 25-40%), while screening, treatment and patient factors (i.e., comorbidity, obesity and smoking) contributed by approximately 15% each toward the survival disparity. The final model accounted for almost all of the cancer survival disparity (HR 1.07, 95% CI 0.80-1.44).
Conclusions: Māori women experience an age-adjusted risk of death from breast cancer, which is more than twice that for NZ European women. Equity-focussed improvements in health care, including increasing mammographic screening coverage and providing equitable quality and timely cancer care, may improve the survival disparity between Māori and NZ European women.
Keywords: Breast cancer; Cancer survival; Ethnicity; Indigenous; Inequity.