Breast cancer is Canada’s second most common cancer and the leading cancer among women, with 1 in 8 women diagnosed with this condition in their lifetime.^1,2 The incidence rate of breast cancer among women in Canada increased annually by 1.9% from 1984 to 1991.³ Since then, it has slightly declined by an average of 0.1% per year, due to enhanced screening and treatment advancements, resulting in a stable trend for almost three decades.^1,3 However, within Ontario, breast cancer rates among First Nations women, initially lower, have gradually increased, now closely aligning with the incidence rates observed in other women in Ontario.⁴

Despite similar incidence rates, significant survival disparities persist between First Nations and non-First Nations women. Studies show that First Nations women are more likely to be diagnosed at a later stage and have higher mortality rates compared to other populations.^5–7 These disparities are often attributed to limited access to early detection and screening programs, cultural barriers, and socioeconomic factors. Additionally, comorbidities, particularly diabetes, contribute to poorer outcomes, with diabetes increasing the risk of cancer in Indigenous populations.^6,8 Treatment disparities, particularly in the use of chemotherapy and radiotherapy, have also been shown to influence survival outcomes.^9,10 These findings highlight the necessity for further analysis to better understand the disparities, while emphasizing the need for a holistic healthcare approach that addresses both cancer and prevalent comorbidities, alongside the unique cultural and geographic challenges faced by First Nations women.

The present study builds upon earlier work that compared cohorts of First Nations and non-First Nations women who were diagnosed with breast cancer between 1995 and 2004 in Ontario and explored the determinants of breast cancer survival.^7,11 Previous research found that survival was more than three times poorer for First Nations women diagnosed at stage I, and the risk of death after a stage I diagnosis was about five times higher for those with a comorbidity other than diabetes.^7,11,12 For First Nations women with diabetes, the hazard of death was more than five times greater compared to those without comorbidities.⁷ The current analysis utilizes more contemporary outcome data and an extended follow-up period to assess if breast cancer survival rates have changed over time, while exploring the influence of factors like prognosis, treatment and socio-economic conditions on breast cancer survival.

The primary objectives of this study are to compare the 10-year survival distribution by stage at breast cancer diagnosis between First Nations and non-First Nations women in Ontario, and to examine the potential influence of other factors on survival by stage within First Nations women. By examining a more recent time period of breast cancer survival among First Nations women, this study aims to assess the effectiveness of the cancer care system in Ontario and identify areas where disparities persist or improvements have been made.

This selection process resulted in a final cohort comprising 282 First Nations women and 670 non-First Nations women, all of whom were diagnosed with an invasive breast cancer and had attended one of the designated RCPs in Ontario (Figure 1). The overall follow-up time for First Nations women was significantly shorter compared to that of non-First Nations women (12.5 and 13.9 years respectively, P=0.0091.

There was a significant difference in the method of detection, with 22% of First Nations women’s breast cancers being screen detected, compared to 29% among non-First Nations women (P=0.0187). Additionally, First Nations women were more frequently diagnosed at later stages of breast cancer (stage II-IV) than non-First Nations women (P=0.0065).

First Nations women had a significantly longer time to diagnosis for subsequent cancers compared to non-First Nations women, with a mean of 10 years versus 7.6 years for non-breast cancers (P=0.0256) and 12 years versus 9.8 years for any cancer (P=0.0278).

Treatment differences were apparent, with First Nations women significantly more likely to undergo intensive surgery, such as mastectomies (38% vs. 27%, P=0.0008), and less likely to receive radiotherapy (67% vs. 75%, p=0.024), compared to non-First Nations women. However, the rates of stage- and age-appropriate treatments were similar across both groups (76% vs. 75%, P=0.516) (Table 1).

Among First Nations women diagnosed with a stage I breast cancer, comorbidities other than diabetes (HR = 3.95, 95% CI = 1.20-12.97) and diabetes (HR = 3.10, 95% CI = 1.09-8.81) significantly increased mortality hazard (Table 4). Chemotherapy was also associated with increased mortality in this group (HR = 4.05, 95% CI = 1.46-11.20), while hormonal therapy was associated with reduced mortality (HR = 0.38, 95% CI = 0.14-0.996). Among First Nations women diagnosed with advanced breast cancer (stages II+), 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.

The present study builds upon the foundational work of Sheppard et al., by utilizing an updated cohort with more recent data, providing a contemporary perspective to assess how survival outcomes have evolved over a longer period.⁷ The results of the current study align with and extend previous research by revealing a positive trend in long-term survival for First Nations women, but highlight gaps that still need attention within the breast cancer community.

After adjusting for age, period of diagnosis, and RCP location, we observed persistent survival differences between First Nations and non-First Nations women. The results of our analyses suggest that these disparities could be influenced by factors such as the higher prevalence of comorbidities, particularly diabetes, among First Nations women, as well as differences in treatment modalities received. Socioeconomic challenges, including income disparities and geographic barriers, may further exacerbate these survival differences by limiting access to timely and comprehensive cancer care. Additionally, cultural and systemic factors could play a role in treatment adherence and healthcare experiences. The findings reinforce the complexity of breast cancer survival among First Nations women, emphasizing that disparities are rooted in factors such as healthcare access, comorbidity prevalence, socioeconomic status, and treatment differences.

These findings highlight the need for culturally tailored healthcare strategies and policies that address both medical and social determinants of health to reduce disparities and improve outcomes for First Nations women.

Our results mark a significant shift in the survival outcomes for First Nations women with breast cancer, particularly in early-stage disease.

In contrast, our earlier findings indicated a significant threefold higher risk of death after a stage I breast cancer 5 years after diagnosis (the current 10-year analysis presents a more encouraging scenario).⁷ The absence of a significant rise in mortality for stage I breast cancer among First Nations women over a decade indicates a favorable change in the survival trends, reflecting improvements in treatment and healthcare access for First Nations women

However, while these results are a positive indication of progress, it is crucial to recognize that the journey towards completely bridging the survival gap between First Nations and non-First Nations women is ongoing.

The existing literature has shown that there are stage-specific breast cancer survival disparities between First Nations and non-First Nations women.

One study reported a significant disparity in breast cancer stage at diagnosis for First Nations women in Manitoba, with a higher likelihood of being diagnosed at later stages compared to other people in this province.⁵ Similarly, another study reported that First Nations people in Canada are more likely to be diagnosed with cancer at later stages compared to non-Indigenous people in Canada, leading to significantly lower survival rates.¹⁸ Advanced-stage cancers often require more aggressive treatments, which may not be as effective as early-stage interventions, thereby influencing overall survival rates negatively. This late-stage diagnosis can be attributed to various factors including limited access to early detection and screening programs, cultural barriers, and socioeconomic factors.⁵

The current findings that comorbidities, particularly diabetes, significantly increase the mortality hazard among First Nations women with breast cancer is consistent with the results observed in the original and subsequent analyses.^7,19 Furthermore, a study focusing on indigenous cancer patients in Australia demonstrated that those with diabetes faced a significant survival disadvantage compared to their non-diabetic counterparts.⁸ This was attributed to a higher incidence of non-cancer deaths, more advanced cancer stages at diagnosis, reduced access to cancer treatment, and a greater prevalence of other comorbidities. These observations align with situations in Manitoba, where diabetes has been shown to increase the risk of several cancers in Indigenous populations.⁶

To address these challenges, strategies such as improved diabetes screening, management, and access to culturally appropriate care are essential.^20,21 Community-based, culturally-tailored interventions, including the use of tools like the FORGE AHEAD clinical readiness consultation, can help ensure that diabetes care is integrated effectively within local First Nations communities.²² These initiatives, combined with efforts to address social determinants of health such as food insecurity and limited access to care,^23,24 are critical to improving survival outcomes for First Nations women with breast cancer and diabetes.

The differences in breast cancer mortality hazard associated with chemotherapy, radiotherapy, and hormonal therapy in our study echo the findings of previous studies that emphasized disparities in breast cancer treatment and subsequent cancer death among Indigenous and non-Indigenous women.⁹ Specifically, the increased mortality hazard associated with radiotherapy in First Nations women with advanced-stage breast cancer and chemotherapy for those with stage I warrants further investigation. It is crucial to note that our study did not assess treatment compliance or factors influencing treatment choice, which could differ between First Nations and non-First Nations women due to geographic disparities and other factors. Given that radiotherapy services are predominantly located in urban centers, First Nations women living in remote or rural areas face additional barriers to accessing these treatments, potentially influencing the observed disparities in survival outcomes.

Our findings also highlight the observation that radiotherapy and hormonal therapy are linked to reduced mortality in stage I breast cancer, aligning with older studies which documented disparities in breast cancer treatment among various racial and ethnic groups.²⁵ For stages II-IV breast cancer, hormonal therapy showed a reduction in mortality risk, suggesting its potential effectiveness across more advanced stages of cancer. This differential impact of treatment modalities warrants the need for careful consideration of treatment approaches in First Nations women, as also discussed by other researchers¹⁰ who noted disparities in cancer treatment and comorbidity status among Indigenous and non-Indigenous populations.

Moreover, these findings emphasize the complexity of treating breast cancer within diverse populations. The effectiveness and risks associated with radiotherapy²⁶ demonstrate that long-term risks such as second cancers and cardiovascular diseases must be weighed against the immediate benefits of reduced recurrence and mortality. This decision-making process is further complicated in settings where access to comprehensive cancer care is limited by geographic and systemic barriers.

Given these complexities, future research should focus on examining the intersection of First Nations identity and treatment modalities to better understand and address the unique healthcare challenges faced by these groups. Such studies are crucial for developing tailored strategies that not only improve survival outcomes but also minimize long-term adverse effects, ensuring equitable and effective cancer care for all populations.

Although this study on breast cancer survival among First Nations women in Ontario offers important insights, there were a few limitations. Firstly, the study spans a decade, a period during which medical practices, diagnostic technologies, and treatment protocols likely evolved, potentially affecting the comparability and relevance of the survival outcomes over time. The statistical power of the study might also be limited, particularly in subgroup analyses, due to the sample size of First Nations women. Moreover, while the OCR had limited data on lifestyle factors and environmental exposures, additional risk factors and access to care variables were obtained from the RCP charts. However, the study may still not fully address other aspects of health behaviors or access to healthcare, which are significant in cancer diagnosis, treatment, and survival. Furthermore, there was a lack of detailed data on whether patients completed the prescribed breast cancer treatments, which is a crucial factor in evaluating treatment effectiveness and survival outcomes. This gap highlights a potential area for future research to better understand the impact of treatment adherence on breast cancer survival among First Nations women.

While differences in survival rates between First Nations and non-First Nations women are apparent, they may be influenced by factors such as age, comorbidity, detection method, and surgery type. However, the evolution from the initial examination of these cohorts marks a significant shift in understanding breast cancer survival among First Nations women. Firstly, it supports the persistence of certain challenges, such as the impact of comorbidities, especially diabetes, while also suggesting the need for stage-specific interventions, the specific effects of different treatments and the influence of geographic location on survival outcomes. Notably, our study brings to light an encouraging improvement in survival rates, particularly in early-stage breast cancer among First Nations women, suggesting positive changes in cancer care strategies and healthcare access over time.

In conclusion, these findings underline the importance of continuous surveillance and the need for adaptive cancer care strategies tailored for First Nations women. It is imperative to recognize the nuanced and evolving landscape of factors affecting breast cancer survival to develop effective, culturally sensitive, and holistic approaches that can further enhance outcomes.²⁷ While acknowledging the strides made, this study reaffirms the commitment to ongoing efforts in research and healthcare practices to sustain and amplify these positive trends in breast cancer survival among First Nations women.

This study has received ethical approval from the University of Toronto Research Ethics Board (REB) and was supported by the Joint Ontario Indigenous Health Committee.

Parts of the material underlying this article are based on data and information provided by Ontario Health (Cancer Care Ontario). Ontario Health is prohibited from making the data used in this research publicly accessible if it includes potentially identifiable personal health information and/or personal information as defined in Ontario law, specifically the Personal Health Information Protection Act (PHIPA) and the Freedom of Information and Protection of Privacy Act (FIPPA). Upon request and approval by the Joint Ontario Indigenous Health Committee, data de-identified to a level suitable for public release may be provided.