Key Points
Question
What are the incidence, mortality, and survival trends in screening program cancers (breast, cervical, and colon) in First Nations people in Ontario, Canada, compared with other Ontario residents?
Findings
This cohort study of more than 12 million people (representing the largest of multiple annual cohorts) found that although trends improved over time for both First Nations people and other Ontario residents, cervical and colon cancer incidence and mortality were higher among First Nations people, while breast cancer incidence and mortality were lower. Survival after cancer diagnosis was lower for First Nations people.
Meaning
These findings suggest that despite progress over time, disparities persist for First Nations people, highlighting the need for better prevention and postdiagnostic care to improve outcomes.
This cohort study examines the incidence, mortality, and survival trends in screening program cancers (breast, cervical, and colon) among First Nations people in Ontario, Canada, compared with other Ontario residents.
Abstract
Importance
Understanding trends among screening program cancers (breast, cervical, and colon) equips researchers, policymakers, and First Nations communities with evidence to inform cancer system improvements.
Objective
To examine cancer incidence, mortality, and survival trends for screening program cancers among First Nations people in Ontario, Canada, compared with other Ontario residents.
Design, Setting, and Participants
This retrospective cohort study examined incidence (1994-2018), mortality (1994-2017), and survival (2007-2019) of breast, cervical, and colon cancers among First Nations people identified from the Indian Registry System linked to the Registered Persons Database and other Ontario residents identified from the Registered Persons Database. The data were analyzed between July 2020 and March 2022.
Main Outcomes and Measures
Baseline characteristics between the First Nations and other Ontario cohorts were compared. Negative binomial regression adjusting for age and sex was used to model annual incidence and mortality. Crude rates were plotted using 3-year moving averages. Cox proportional hazards regression, adjusting for age, sex, comorbidity, and cancer stage, was used to model survival. Interactions were tested for all models.
Results
The largest annual cohort included 146 498 First Nations people (median [IQR] age, 41 [28-55] years; 50.7% male) and 11 840 783 other Ontario residents (median [IQR] age, 48 [33-62] years; 51.1% female). Compared with other Ontario females, First Nations females had lower breast cancer incidence (rate ratio [RR], 0.77 [95% CI, 0.73-0.82]) and mortality (RR, 0.79 [95% CI, 0.70-0.90]). Cervical cancer incidence and mortality were higher in First Nations females (RR, 1.47 [95% CI, 1.23-1.70] and 2.26 [95% CI, 1.78-2.88], respectively); however, over time, both rates declined more rapidly among First Nations females. Colon cancer incidence was higher for First Nations people; those aged 40 to 49 years had a similar elevated risk to those aged 50 to 74 years (incidence RR, 1.27 [95% CI, 1.06-1.51] and 1.29 [95% CI, 1.20-1.40], respectively). First Nations people had higher colon cancer mortality (RR, 1.18 [95% CI, 1.07-1.31]). Once diagnosed, First Nations people were more likely to die compared with other Ontario residents (breast cancer: hazard ratio, 1.51 [95% CI, 1.28-1.76]; cervical cancer: hazard ratio, 1.60 [95% CI, 1.12-2.27]; colon cancer: hazard ratio, 1.19 [95% CI, 1.07-1.32]).
Conclusions
This cohort study of First Nations people in Ontario and other Ontario residents suggests that clear disparities persist despite progress over time. Cancer prevention, screening programs, and care systems for Indigenous peoples in Ontario need optimization.
Introduction
There are 3 constitutionally recognized Indigenous populations in Canada: the First Nations, Métis, and Inuit peoples. Each population is distinct based on unique histories, geographies, knowledge, and experiences. More than 70 distinct languages have been reported among 1 807 250 Indigenous peoples in the country.1 Indigenous populations in Canada are young and growing, with the largest populations residing in the province of Ontario.1 This project included only First Nations people in Ontario who have registered status under the Indian Act2 due to data limitations that preclude identifying Métis and Inuit peoples, as well as First Nations people without status. First Nations status is a colonial construct determined and maintained by the Canadian government and does not necessarily align with First Nations community self-identification or self-determination. Colonial mechanisms of determining First Nations status have been described elsewhere (eg, denial of status to descendants of communities that refused to sign treaties, forced enfranchisement, loss of status for First Nations females who married men without status, onerous application process for status).3
Ontario Health oversees the operation of Ontario’s population-based cancer screening programs. The Ontario Breast Screening Program, the Ontario Cervical Screening Program, and ColonCancerCheck, were launched in 1990, 2000, and 2008, respectively. Each program has established screening guidelines.4,5,6 The Ontario Lung Screening Program is the newest program that started provincial rollout in 2021. As such, lung cancer findings will be reported separately.
Although historically, Indigenous peoples in Canada were at lower risk for cancer compared with non-Indigenous people, this is no longer the case.7,8,9,10 Despite the generally effective provincial screening programs, Indigenous peoples continue to experience a high burden of cancer.7,8,9
From 1991 to 2010, the incidence of colon and cervical cancers was higher and survival was lower for First Nations people in Ontario compared with non-Indigenous people.11,12 First Nations females were reported as having a lower incidence of breast cancer; however, incidence was increasing and survival was worse compared with non-Indigenous females in the province.11,13 These studies were not able to account for stage at cancer diagnosis and the presence of comorbidity at diagnosis, both of which have been associated with poorer breast cancer survival among First Nations females in Ontario.12,14 In subsequent community-based research and ongoing engagement with First Nations communities and leadership across the province, communities validated the findings and called for new research, as they observed community members often being diagnosed with cancers at younger ages, specifically before they met the minimum age eligibility requirements for the provincial screening programs.15,16 The aim of this study was to address these concerns with updated and more comprehensive datasets. We report on age- and sex-adjusted incidence and mortality and age-, sex-, comorbidity-, and stage-adjusted survival for screening program cancers (breast, cervical, and colon) in a contemporary population of First Nations adults in Ontario.
Methods
This cohort study involved Indigenous partners in the project design and implementation through the Indigenous Cancer Care Unit (ICCU) at Ontario Health. The Joint Ontario Indigenous Health Committee (JOIHC) comprises members from political territorial organizations and Indigenous organizations. The JOIHC advises the ICCU and provided the directive for this study and guidance during the project. The project team consisted of 2 First Nations persons (A.K. and A.I.), 6 individuals with years of meaningful work in the field of Indigenous health (A.J.S., A.K, S.L., L.S., A.M.C., and J.T.), 3 trainees in Indigenous peoples health (L.S., A.I., and S.H.), 4 leaders in the cancer screening system (A.M.C., R.K., C.M.T., and J.T.), and 3 analytic experts (R.S., N.L., and C.M.T.). We followed First Nations research principles of ownership, control, access, and possession.17 Approval for use of the data was obtained from the Chiefs of Ontario First Nations Data Governance Committee, the Grand Council Treaty #3 Health Council, and the Kenora Chiefs Advisory. Finally, through the ICCU and JOIHC, Indigenous partners were included in the review and interpretation of results and knowledge translation products and assisted in reporting back to the community (eFigure 1 in Supplement 1). Institutional ethical approval of this research protocol was obtained from the Sunnybrook Health Sciences Centre and University of Toronto Research Ethics Boards. We used data securely housed at ICES (formerly known as the Institute for Clinical Evaluative Sciences), an independent, nonprofit research institute whose legal status under Ontario’s health information privacy law allows it to collect and analyze health care and demographic data, without consent, for health system evaluation and improvement. The ICES databases, linked by unique encoded identifiers, used for the analyses, are described in eTable 1 in Supplement 1. Parts of this material are based on data and/or information compiled and provided by the Ontario Ministry of Health. The study followed the Reporting of Studies Conducted Using Observational Routinely Collected Health Data (RECORD)18 and the Consolidated Criteria for Strengthening the Reporting of Health Research Involving Indigenous Peoples (CONSIDER)19 reporting guidelines.
Study Design and Cohorts
We examined all (not just screen-detected) breast, cervical, and colon cancers separately, reporting (1) annual cancer incidence and annual cancer mortality and (2) time from cancer diagnosis to death. Because of data availability, the study periods varied: cancer incidence, from January 1, 1994, to December 31, 2018; cancer mortality, January 1, 1994, to December 31, 2017; and time from cancer diagnosis to death of any cause, January 1, 2007, to March 31, 2019.
Annual Cancer Incidence and Cancer Mortality
We identified adults aged 18 years or older and alive as of January 1 of each year using the Registered Persons Database. From these overall population cohorts, we created First Nations (using the Indian Register Service) and other Ontario cohorts for each year of the study period. We excluded all identified First Nations and Métis persons (using the Métis Citizenship Registry) from the other Ontario cohorts. During the observation period, individual-level race- and ethnicity-based data were not collected in the datasets used in this study. An Ontario Health Insurance Plan (OHIP) number is required for linkages. For each annual cohort, other Ontario residents were required to be eligible for OHIP coverage as of January 1 of that year, while First Nations people, who may receive some of their health care outside of OHIP via federally funded nursing stations, were retained as long as they had OHIP coverage at any time prior to or on that same date. Cohorts were restricted to females for the breast and cervical cancer analyses. For the incidence trend analyses, persons diagnosed with the relevant screening program cancer prior to January 1 of each year were excluded (description of cohort creation provided in eTable 2 in Supplement 1).
Time From Cancer Diagnosis to Death
Cohorts were limited to persons diagnosed with the relevant screening program cancer from January 1, 2007, to December 31, 2018, due to limitations in the cancer stage data. From the diagnosis date, each individual in the cohort was followed up until March 31, 2019, for all-cause mortality (description of cohort creation provided in eTable 3 in Supplement 1).
Variable Definitions
The main comparison of interest was First Nations people compared with other Ontario residents. New screening program cancers were grouped according to the Surveillance, Epidemiology, and End Results Site Recode for International Classification of Diseases for Oncology, 3rd Edition; in situ breast cancer diagnoses were excluded.20 Age categorization varied depending on the analysis and the cancer, as described in the next section. We measured comorbidity using the number of major John Hopkins Aggregated Diagnosis Groups (0, 1, ≥2) based on a preliminary exploratory analysis. Stage was categorized as I, II, III, IV, or other (mostly due to missing stage).
Statistical Analysis
Annual Cancer Incidence and Cancer Mortality
Annual age-specific and sex-specific (colon cancer only) incidence rates among First Nations people and other Ontario residents, standardized to the 2001 Ontario census population, were calculated for each cancer from 1994 to 2018. Age was categorized as 18 to 39 years, 40 to 49 years, 50 to 74 years, and 75 years or older for the breast and colon cancer analyses and as 18 to 39 years, 40 to 49 years, 50 to 70 years, and 71 years or older for the cervical cancer analysis to align with eligibility ages for the relevant screening programs.4,21,22 To visualize trends over time, the 3-year moving average of age-adjusted and sex-adjusted incidence for each cancer was plotted and a line of best fit derived using linear regression. Using a similar approach, we investigated the annual age-specific and sex-specific (colon cancer only) cancer mortality among First Nations people and other Ontario residents from 1994 to 2017.
We used negative binomial regression models to compare the cancer incidence rate (or cancer mortality rate) between First Nations people and other Ontario residents, adjusting for year, sex, and age group for each cancer type. The dependent variable for the models was the number of incident cancer cases (or for the model of mortality rate, the number of cancer-specific deaths). The natural logarithm of the population size was used as an offset term. Rate ratios (RRs) comparing First Nations people with other Ontario residents were estimated. Variation in RRs by age or period were tested, using interactions between the main comparator and age group, then main comparator and observation period of diagnosis (1994-2000, 2001-2014, 2015-2018).
Time From Cancer Diagnosis to All-Cause Death
The index date was the diagnosis date. Baseline characteristics at index date for the First Nations and other Ontario cohorts were summarized. The cumulative incidence with 95% CIs was used to illustrate the crude probability of death over time in First Nations people vs other Ontario residents (log-rank test performed to compare the unadjusted risk of death). We modeled the hazard of all-cause death among First Nations people compared with other Ontario residents using multivariable Cox proportional hazards regression models, adjusting for age at diagnosis, sex (for colon cancer only), stage at diagnosis, comorbidity, and year of diagnosis (modeled as continuous). Age was categorized as 18 to 49 years, 50 to 59 years, 60 to 69 years, 70 to 79 years, 80 years or older. We performed sensitivity analyses by modeling the cumulative incidence of cancer death for the 2 groups, using noncancer death as a competing event.
The data analysis was performed between July 2020 and March 2022. The threshold for significance was set at a 2-sided P < .05. The statistical analysis was performed using SAS, version 9.4 (SAS Institute Inc).
Results
Annual Cancer Incidence and Cancer Mortality
Separate cohorts were created for each year of the study (eTable 2 in Supplement 1). The largest annual cohort included 146 498 First Nations people (median [IQR] age, 41 [28-55] years; 49.3% female and 50.7% male) and 11 840 783 other Ontario residents (median [IQR] age, 48 [33-62] years; 51.1% female and 48.9% male). Table 1 presents the number of First Nations people and other Ontario residents in the baseline population and who experienced new screening program cancer events and cancer-related death at 3 time points during the study period. The sample sizes for the First Nations cohorts were small compared with other Ontario residents in each annual cohort, for example, new cancers ranged from 6 persons (cervical cancer in 1994) to 91 persons (colon cancer at the end of the observation period) across the different First Nations cancer cohorts.
Table 1. Population at Risk, New Cancers, and Cancer Deaths in First Nations People in Ontario and Other Ontario Residents at the Beginning, Middle, and End-of-Study Observation Periods.
| Cohort and years | Incidence | Mortality | ||||||
|---|---|---|---|---|---|---|---|---|
| First Nations people | Other Ontario residents | First Nations people | Other Ontario residents | |||||
| Population at risk, No. | New cancers, No. | Population at risk, No. | New cancers, No. | Population at risk, No. | Cancer deaths, No. | Population at risk, No. | Cancer deaths, No. | |
| Breast cancer | ||||||||
| 1994 | 40 484 | 33 | 4 174 939 | 5870 | 40 654 | 6 | 4 225 084 | 1822 |
| 2006 | 56 607 | 52 | 5 145 407 | 7720 | 57 078 | 13 | 5 234 456 | 1784 |
| End of observation perioda | 70 725 | 88 | 5 932 240 | 10 055 | 72 172 | 18 | 6 049 784 | 2005 |
| Cervical cancer | ||||||||
| 1994 | 40 542 | 6 | 4 218 127 | 534 | 40 654 | ≤5b | 4 225 084 | 154 |
| 2006 | 56 933 | 10 | 5 225 436 | 494 | 57 078 | ≤5b | 5 234 456 | 156 |
| End of observation perioda | 71 403 | 11 | 6 058 336 | 621 | 72 172 | 0 | 6 049 784 | 151 |
| Colon cancer | ||||||||
| 1994 | 82 006 | 31 | 8 204 635 | 5509 | 82 137 | 8 | 8 235 208 | 2073 |
| 2006 | 115 660 | 45 | 10 197 375 | 7088 | 116 006 | 23 | 10 247 596 | 2556 |
| End of observation perioda | 144 609 | 91 | 11 804 839 | 7109 | 146 498 | 30 | 11 840 783 | 2756 |
End of study observation period was 2018 for incidence and 2017 for mortality.
Range reported to maintain concealment of small cells.
The annual age-standardized and sex-standardized incidence and mortality for breast, cervical, and colon cancers (plotted using 3-year moving averages) declined over the study period for both First Nations people and other Ontario residents. Incidence and mortality rates were lower among First Nations females for breast cancer but higher for the other cancers (Figure 1; eTable 4 in Supplement 1). The adjusted incidence and mortality RRs over the entire study period are presented in Table 2. Compared with other Ontario females, First Nations females had a lower incidence rate of breast cancer (RR, 0.77 [95% CI, 0.73-0.82]) and a lower mortality rate for breast cancer (RR, 0.79 [95% CI, 0.70-0.90]) (Figure 1A and B). The incidence and mortality rates for cervical cancer were higher in First Nations compared with other Ontario females (RR, 1.47 [95% CI, 1.23-1.70] and 2.26 [95% CI, 1.78-2.88], respectively) (Figure 1C and D). Despite sharper declines in rates for First Nations females during the study period (Figure 1C and D), the interaction between main comparator and observation period was not significant for incidence (P = .43) or mortality (P = .05). First Nations people had a higher diagnosis rate of colon cancer (Figure 1E), with a significant interaction between the main comparator and age group (P = .001). First Nations people had a higher incidence of colon cancer than other Ontario residents in both the 40- to 49-year age group (RR, 1.27 [95% CI, 1.06-1.51]) and 50- to 74-year age group (RR, 1.29 [95% CI, 1.20-1.40]), with a similar RR observed among those who were not eligible for screening (ie, aged 40-49 years) and those who were (ie, aged 50-74 years). First Nations people had a higher rate of dying of colon cancer than other Ontario residents (RR, 1.18 [95% CI, 1.07-1.31]) (Figure 1F; Table 2). There was no significant interaction between the main comparator and age group or observation period for colon cancer death.
Figure 1. Scatter Plots of 3-Year Moving Average of Annual Age-Standardized and Sex-Standardized (Colon Cancer Only) Incidence and Mortality of Screening Cancers.
Lines indicate the best fit (using linear regression) in First Nations people in Ontario and other Ontario residents over the study period. Standardization was performed using the 2001 Ontario population.
Table 2. Incidence and Mortality of Breast, Cervical, and Colon Cancer in Ontario During the Study Period in First Nations People in Ontario Compared With Other Ontario Residentsa.
| Variable | RR (95% CI)b | ||
|---|---|---|---|
| Breast cancer | Cervical cancer | Colon cancer | |
| Incidence of new cancers | |||
| First Nations people compared with other Ontario residents | 0.77 (0.73-0.82) | 1.47 (1.23-1.70) | NRc |
| First Nations people compared with other Ontario residents by age group, y | |||
| 18-39 | NR | NR | 0.82 (0.58-1.15) |
| 40-49 | NR | NR | 1.27 (1.06-1.51) |
| 50-74 | NR | NR | 1.29 (1.20-1.40) |
| ≥75 | NR | NR | 1.01 (0.89-1.15) |
| Mortality | |||
| First Nations people compared with other Ontario residents | 0.79 (0.70-0.90) | 2.26 (1.78-2.88) | 1.18 (1.07-1.31) |
Abbreviations: NR, not reported; RR, rate ratio.
Study period was 1994 to 2018 for incidence and 1994 to 2017 for mortality.
Adjusted for year, age group, and sex (for colon cancer only).
P = .001 for the interaction between main comparator and age group.
Time From Cancer Diagnosis to All-Cause Death
Between 2007 and 2018, 713 breast, 101 cervical, and 794 colon cancers were diagnosed among First Nations people in Ontario (eTable 3 in Supplement 1). Table 3 shows the baseline characteristics of the First Nations people and other Ontario cohorts. At the time of diagnosis, First Nations people were significantly younger than other Ontario residents (breast cancer: median [IQR], 59 [50-67] vs 61 [50-71] years; P < .001; cervical cancer: median [IQR], 42 [35-51] vs 47 [38-59] years; P = .001; colon cancer: median [IQR], 63 [55-71] vs 69 [60-79] years; P < .001) and in the breast cancer cohort only, had significantly more comorbidities (145 with ≥2 comorbidities [20.3%] vs 18 690 [18.7%]; P = .02), while the distribution of sex and stage were similar for First Nations people and other Ontario residents. Figure 2 displays the crude cumulative probability of all-cause death for each cancer among First Nations people and other Ontario residents during the follow-up period. After adjustment for age group, year of diagnosis, comorbidity, and stage at diagnosis (eTable 5 in Supplement 1), First Nations females had a significantly higher rate of dying after a breast and cervical cancer diagnosis compared with other Ontario females (hazard ratio, 1.51 [95% CI, 1.28-1.76] and 1.60 [95% CI, 1.12-2.27], respectively). Similarly, First Nations people had a higher rate of dying after a colon cancer diagnosis compared with other Ontario residents (hazard ratio, 1.19 [95% CI, 1.07-1.32]). Findings were consistent in analyses accounting for the competing event of noncancer death (eFigure 2 in Supplement 1). A sensitivity analysis that included First Nations people who did not have an OHIP record prior to January 1 of each year found either no or very few incident cancer cases each year among those who were excluded (eTable 6 in Supplement 1).
Table 3. Characteristics of Breast, Cervical, and Colon Cancer Cohorts for First Nations People in Ontario and Other Ontario Residents, 2007-2018.
| Characteristic | Breast cancer | Cervical cancer | Colon cancer | ||||||
|---|---|---|---|---|---|---|---|---|---|
| First Nations people, No. (%) | Other Ontario residents, No. (%) | P value | First Nations people, No. (%) | Other Ontario residents, No. (%) | P value | First Nations people, No. (%) | Other Ontario residents, No. (%) | P value | |
| No. of cancers | 713 | 99 697 | NA | 101 | 6069 | NA | 794 | 76 616 | NA |
| Age, median (IQR), y | 59 (50-67) | 61 (50-71) | <.001 | 42 (35-51) | 47 (38-59) | .001 | 63 (55-71) | 69 (60-79) | <.001 |
| Age group, y | |||||||||
| 18-49 | 164 (23.0) | 20 713 (20.8) | <.001 | 73 (72.3) | 3429 (56.5) | .03 | 98 (12.3) | 6246 (8.2) | <.001 |
| 50-59 | 208 (29.2) | 24 763 (24.8) | 12 (11.9) | 1154 (19.0) | 209 (26.3) | 12 895 (16.8) | |||
| 60-69 | 218 (30.6) | 25 511 (25.6) | 9 (8.9) | 788 (13.0) | 243 (30.6) | 19 191 (25.0) | |||
| 70-79 | 97 (13.6) | 17 375 (17.4) | ≤5 (5.0) | 401 (6.6) | 179 (22.5) | 20 247 (26.4) | |||
| ≥80 | 26 (3.6) | 11 335 (11.4) | ≤5 (2.0) | 297 (4.9) | 65 (8.2) | 18 037 (23.5) | |||
| Sex | |||||||||
| Female | 713 (100) | 99 687 (100) | NA | 101 (100) | 6069 (100) | NA | 345 (44.6) | 34 941 (45.6) | .57 |
| Male | 0 | 0 | 0 | 0 | 449 (55.4) | 41 675 (54.4) | |||
| Major comorbiditiesa | |||||||||
| ≥2 | 145 (20.3) | 18 690 (18.7) | .02 | 12 (11.9) | 880 (14.5) | .49 | 207 (26.1) | 21 283 (27.8) | .14 |
| 1 | 249 (34.9) | 31 030 (31.1) | 34 (33.7) | 1740 (28.7) | 244 (30.7) | 24 909 (32.5) | |||
| 0 | 319 (44.7) | 49 977 (50.1) | 55 (54.5) | 3449 (56.8) | 343 (43.2) | 30 424 (39.7) | |||
| Cancer stage | |||||||||
| I | 277 (38.8) | 41 242 (41.4) | .07 | 45 (44.6) | 2940 (48.4) | .96 | 134 (16.9) | 15 373 (20.1) | .23 |
| II | 254 (35.6) | 34 744 (34.8) | 17 (16.8) | 933 (15.4) | 196 (24.7) | 17 657 (23.0) | |||
| III | 113 (15.8) | 12 665 (12.7) | 16 (15.8) | 886 (14.6) | 218 (27.5) | 20 508 (26.8) | |||
| IV | 33 (4.6) | 4730 (4.7) | 10 (9.9) | 561 (9.2) | 137 (17.3) | 13 331 (17.4) | |||
| Otherb | 36 (5.0) | 6316 (6.3) | 13 (12.9) | 749 (12.3) | 109 (13.7) | 9747 (12.7) | |||
Abbreviation: NA, not applicable.
Number of major Johns Hopkins Aggregated Diagnosis Group comorbidities, excluding cancer, prevention, dental, and pregnancy categories.
Included missing or unknown.
Figure 2. Survival Curves of Crude Probability and Adjusted Hazard of All-Cause Death Among First Nations People in Ontario Compared With Other Ontario Residents, 2007-2018.
Analyses were adjusted for age group, sex (colon cancer only), year of diagnosis, comorbidity, and stage at diagnosis. Shading indicates the 95% CI. HR indicates hazard ratio.
Discussion
This cohort study found that overall, the incidence and mortality of cervical, breast, and colon cancers improved for First Nations people; however, cancer survival remained significantly lower compared with other Ontario residents, even after adjustment for important prognostic factors, such as stage and comorbidity at diagnosis. Compared with other Ontario residents, First Nations people were at elevated risk of diagnosis and dying of these cancers with the notable exception of breast cancer. The cervical cancer trends were particularly encouraging given the significantly elevated risks in First Nations females at the start of the study period. We hypothesize that these trends may reflect communities’ advocacy efforts to increase participation with screening and human papillomavirus prevention through initiatives such as short, animated educational video series in Ojibwe and Cree23; hosting screening events24; and screening at mobile centers,25 since human papillomavirus vaccination did not begin recently enough in Ontario to benefit individuals in our study (8th-grade girls in 2007-2008 and boys in 2016). The risk of colon cancer in First Nations people was significantly elevated compared with other Ontario residents not only among screen-eligible persons but also in those aged 40 to 49 years, who were not yet eligible for screening according to provincial guidelines.
First Nations people in Ontario and Indigenous populations elsewhere experience poorer cancer survival compared with their non-Indigenous counterparts; however, trends in cancer incidence and mortality are different across the different jurisdictions.26,27,28,29,30,31,32 Systemic and environmental factors, the effects of colonialism, and inequities in social determinants of health may contribute to First Nations people experiencing a higher prevalence of cancer risk factors, which may partly explain these trends. These risk factors, which are shaped by inequities in social determinants of health, include tobacco use, alcohol consumption, obesity, inadequate physical activity, and inadequate consumption of healthy foods.33,34,35 The presence of comorbidities such as diabetes, which disproportionally affects First Nations people in Ontario, may also contribute to the increased cancer burden and decreased cancer survival in this population.12,36 While we used the best measure of comorbidity based on exploratory analyses, we may have undercounted the true frequency, severity, and scope of conditions. Furthermore, the presence of social and systemic barriers to accessing health care for Indigenous peoples may decrease uptake of screening tests among First Nations people,37,38,39 an issue that has been reported in Ontario.33,40 We found that First Nations people aged 40 to 49 years were at elevated risk of colon cancer compared with other Ontario residents in the same age group. A younger age at diagnosis for colon cancer among Indigenous populations in Australia and the US has also been described.41,42 In the US, recommendations have been made to lower the start age for colon cancer screening to 40 years for Alaska Native people,41 while the screening start age was lowered to 45 years for all Australians in 2023.43 While there are risks associated with reducing the age of eligibility44 (eg, screening procedure–related complications, burden to the health care system), lowering the age to 45 years for all Canadians could result in overall cost savings and improved long-term outcomes.45
Despite some improvement in screening program cancer incidence and mortality among First Nations people, the observed poorer survival is highly concerning and warrants further investigation. Across Canada, as noted elsewhere, Indigenous peoples experience significant health disparities and inequities,46,47 which may have contributed to our findings. These health inequities may be partly due to the transgenerational effects of historic and contemporary colonial structures, resulting in Indigenous peoples experiencing racism, social exclusion, and lack of equity and self-determination in the Canadian context.37,46,47 Furthermore, many Indigenous peoples in Ontario live in rural and remote parts of the province, resulting in substantial geographic barriers to accessing health care services. Future analyses should examine cancer outcomes based on place of residence (urban or rural and inside or outside a First Nations community); having a primary care practitioner; and access, wait time, and ability to complete treatment to further elucidate causes for the observed survival inequality, with the goal of informing policy and creating systems to minimize health disparities.
Limitations
Our study had some limitations. Age was standardized to the 2001 Ontario population and not to the 1960 World population13 to apply findings more easily to cancer programing in the province; however, it may limit comparisons to past work. The lack of ethnic, racial, and Indigenous identifiers in Canadian health databases, including most used here, present challenges to this type of work. For this study, we used the Indian Register Service to identify First Nations people who were then linked to other Ontario Health data sources. While the Indian Register Service provides the most comprehensive, currently available way to identify First Nations people in Ontario, there are important limitations. As a registry of only First Nations people with status, which is a colonial construct, the Indian Register Service excludes at least 36% of First Nations people in Ontario who do not have status; therefore, the Indian Register Service provides an incomplete measure of First Nations people in the province (eTable 1 in Supplement 1).3,48 Any resulting misclassification would bias toward the null and would not affect findings, with the possible exception of breast cancer incidence and mortality. Since we excluded First Nations people who had never had an OHIP record, a sensitivity analysis was conducted and found either no or very few incident cancer cases each year among those who were excluded (eTable 6 in Supplement 1).
Conclusions
This cohort study suggested that some outcomes for cancer screening program cancers are improving for First Nations people in Ontario; however, there are clear and persistent disparities that require attention. Further work is needed to understand cancer prognostic factors, to optimize cancer prevention strategies and cancer screening programs (including the start age for colon cancer screening), to understand how Indigenous peoples in Ontario experience the cancer care system, and where barriers to equitable care exist. These data, as well as global trends in early-onset colon cancer, support careful review of the start age for colon cancer screening. Our findings validate community concerns and will be explored further in future work already under way. The ultimate goal of this work is to reduce cancer burden and cancer care inequities for Indigenous peoples. The approach taken and lessons learned in Ontario are expected to be relevant to other countries with distinct Indigenous populations, such as the US, Australia, and New Zealand.
eFigure 1. Aim 1 Community-Facing Infographic
eFigure 2. Crude Probability and Adjusted Hazard of Cancer Death
eTable 1. Description of Databases Used in the Study
eReferences.
eTable 2. Cohort Creation for the Incidence and Mortality Analyses for First Nations People and Other Ontario Residents
eTable 3. Cohort Creation for the Survival Analyses (Breast, Cervical, and Colon Cancers) for First Nations People and Other Ontario Residents, 2007-2018
eTable 4. Crude and 3-Year Moving Average Age- and Sex-Standardized Breast, Cervical, and Colorectal Cancer Incidence Rates in Ontario First Nations People and Other Ontario Residents
eTable 5. Adjusted Hazard Ratios for All-Cause Death in First Nations People vs Other Ontario Residents Among Patients Diagnosed With Breast, Cervical, and Colon Cancer, 2007-2018
eTable 6. Incident Cancer Cases in Each Specific Year Among First Nations People Who Were Excluded Due to No OHIP Eligibility on or Before January 1 of That Year
Data Sharing Statement
References
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Associated Data
This section collects any data citations, data availability statements, or supplementary materials included in this article.
Supplementary Materials
eFigure 1. Aim 1 Community-Facing Infographic
eFigure 2. Crude Probability and Adjusted Hazard of Cancer Death
eTable 1. Description of Databases Used in the Study
eReferences.
eTable 2. Cohort Creation for the Incidence and Mortality Analyses for First Nations People and Other Ontario Residents
eTable 3. Cohort Creation for the Survival Analyses (Breast, Cervical, and Colon Cancers) for First Nations People and Other Ontario Residents, 2007-2018
eTable 4. Crude and 3-Year Moving Average Age- and Sex-Standardized Breast, Cervical, and Colorectal Cancer Incidence Rates in Ontario First Nations People and Other Ontario Residents
eTable 5. Adjusted Hazard Ratios for All-Cause Death in First Nations People vs Other Ontario Residents Among Patients Diagnosed With Breast, Cervical, and Colon Cancer, 2007-2018
eTable 6. Incident Cancer Cases in Each Specific Year Among First Nations People Who Were Excluded Due to No OHIP Eligibility on or Before January 1 of That Year
Data Sharing Statement
