A Decade of Breast Cancer in Ontario: Survival Differences Between First Nations and Non-First Nations Women

Background: Breast cancer is the most common cancer among women in Canada, with rising incidence in First Nations (FN) women. This study confirms persistent survival disparities between FN and non-FN women, with updated findings over an extended follow-up period. Methods: Data from the Ontario Cancer Registry, linked to the Indian Registration System, included 282 FN and 670 frequency matched non-FN women diagnosed with invasive breast cancer from 1995-2004. Survival outcomes were assessed up to 2019, analyzing 10-year survival rates by cancer stage and other factors. Results: Unadjusted Kaplan-Meier curves showed lower 10-year survival for FN women (76%) compared to non-FN women (87%) for stage I breast cancer. After adjusting for age, comorbidity, detection method, and surgery severity, no significant difference in mortality hazard was found. Among FN women diagnosed with stage I breast cancer, diabetes (HR = 3.10, 95% CI = 1.09-8.81) and chemotherapy (HR = 4.05, 95% CI = 1.46-11.20) were associated with increased mortality hazard, while hormonal therapy was associated with reduced mortality hazard (HR = 0.38, 95% CI = 0.14-0.996). Among FN women with advanced-stage breast cancer (stages II-IV), diabetes (HR = 1.74, 95% CI = 1.02-2.98) and radiotherapy (HR = 1.88, 95% CI = 1.07-3.29) were associated with increased mortality hazard. Conclusion: Disparities in survival rates between FN and non-FN women may be influenced by factors such as age, comorbidity, detection method, and surgery type. This study shows encouraging improvement over time and advocates for actionable changes to close the survival gap and enhance treatment outcomes for FN women.