Target journal: Lancet Oncology
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Abstract (semi-structured summary; 5 paragraphs; 333/300 words)
Background: Indigenous populations in Canada exhibit higher rates of cancer incidence and mortality compared to non-indigenous populations. Radiotherapy is an important component of cancer treatment, but little information exists on access to radiotherapy among this population.
Methods: We conducted a univariate analysis to explore the relationship between age-standardized all-cancer mortality-to-incidence ratios (MIRs) from 2010 to 2012, and proportion of self-identified Aboriginals per health region in Canada. High multicollinearity was observed between the proportion of Aboriginals variable and other sociodemographic factors; therefore, a multiple linear regression model was not possible. We stratified our two independent variables of interest (proportion of self-identified Aboriginals, and distance to radiotherapy centre) using an exploratory recursive partitioning approach, and conducted one-way analyses of variance and non-parametric Wilcoxon Method comparisons to explore differences between the created groups and their impact on MIR.
Findings: Health regions with a higher proportion of self-identified Aboriginals were significantly associated with higher all-cancer MIR in univariate analysis (r2 = 0.32, p < .0001). When stratified, health regions inhabited by < 23% versus ≥ 23% of Aboriginals had significantly lower MIR (0.42 vs. 0.53, respectively; p < .0001) and shorter Euclidean distance to nearest radiotherapy centre (121 kilometres vs. 799 kilometres, respectively; p < .0001). MIRs in health regions inhabited by ≥ 23% Aboriginals were not significantly different based on distance (greater versus less than 922 kilometres; p = .158); however, both groups had significantly higher MIRs compared to health regions with < 23% Aboriginals, regardless of whether they were greater or less than 37 kilometres away (all p < .01). Health regions with < 23% Aboriginals located ≥ 37 kilometres away from nearest radiotherapy centre also had significantly higher MIRs compared to those < 37 kilometres away (p < .01).
Interpretation: Regions inhabited by a larger proportion of indigenous populations are located further away from the nearest radiotherapy centre, but distance does not completely explain these regions’ poorer oncologic outcomes. Further exploration and identification of other contributing factors to this population’s high MIR is required.
Funding: None.
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INTRODUCTION
The cancer burden among indigenous populations worldwide is significant, with higher rates of cancer mortality reported across numerous countries including Australia \cite{Cunningham_2008}\cite{Condon_2014}, the United States \cite{White_2014} and the Polynesian islands \cite{Dachs_2008}, when compared to their non-indigenous counterparts. Cancer incidence is higher among indigenous populations for some cancer sites but not others \cite{Moore2015}; however, poorer survival appears to be consistent when considering all cancers combined, and for most sub-sites (\cite{Cunningham_2008}\cite{Condon_2014}\cite{White_2014}\cite{Dachs_2008}).
Such disparities in cancer mortality are reflected among the indigenous populations in Canada as well. In Canada, about 4% of the total population is made up of the indigenous people, who are recognised by the Canadian Constitution as "Aboriginal" and consists of three groups: First Nations (approximate population 850,000), Métis (about 450,000) and Inuit (about 59,000) \cite{inuit}. Poorer cancer outcomes have been reported among the Canadian Aboriginal population, including a recent national study demonstrating worse survival among First Nations people compared with non-Aboriginals for 14 of 15 of the most common cancers \cite{Withrow_2016}. Poorer survival was also reported among First Nations peoples in British Columbia compared to non-First Nations peoples, in 10 of 15 cancer sites studied in women, and 10 of 12 cancer sites studied in men \cite{McGahan_2017}. Similar findings have been reported for First Nations with head and neck cancers in Alberta \cite{Erickson_2015}, and across multiple cancer sites in Ontario \cite{Nishri_2014}, although in one Alberta study, survival outcomes were not significantly different among Métis versus non-Métis cancer patients \cite{Sanchez_Ramirez_2016}. In addition, all-cancer mortality rates in the Yukon territory were significantly higher compared to national and provincial rates from 1999 to 2013, and while the population in this study was not limited to Aboriginals, a considerably higher proportion of the Yukon population is Aboriginal (23%), compared to the national average (4%) \cite{Simkin_2017}.
Radiotherapy is an important component of cancer treatment. However, poorer access to, or uptake of cancer treatments once diagnosed, such as radiotherapy, has been reported as a significant reason underpinning the disparities in cancer outcomes seen between Aboriginal and non-Aboriginal populations (\cite{Ahmed_2015},\cite{Coory2008},\cite{Gibberd_2016}). Indeed, in one Australian study, a difference of 46% versus 72% uptake in active treatment (including chemotherapy, radiotherapy or surgery) was found for Aboriginal versus non-Aboriginal lung cancer patients, which was thought to explain most of the observed survival deficit (a median survival of 4.3 versus 10.3 months, respectively)\cite{Coory2008}; similar findings were reported again within the Australian Aboriginal population, for all-cancers overall \cite{Valery_2006}. Even when patients choose to purse treatment, delays to receiving treatment exist and are not uniform among Aboriginals versus non-Aboriginals; for example, a study in New Zealand found a higher proportion of Māori women experienced delays longer than thresholds for adjuvant radiotherapy and chemotherapy compared to New Zealand European women, which may have contributed towards the higher breast cancer mortality observed among this population \cite{Seneviratne_2014}.
The barriers to accessing cancer services among indigenous populations are multi-factorial, and include mistrust of the health system, stigma, and a lack of cultural understanding within the health system \cite{McGrath2006}, likely stemming from a history of colonization. Among such barriers, distance and the resulting travel burden have been repeatedly shown to significantly impact access to cancer services, negatively influencing all aspects of a cancer patient's journey from stage at diagnosis to quality of life \cite{Ambroggi_2015}. Radiotherapy is no exception to this, and in fact, longer distance to radiotherapy centre has been cited as one of the most important barriers to accessing this treatment \cite{Gillan2012}, given the financial burden and expenses required to travel for treatment \cite{best}. Therefore, as Canadian Aboriginals are more likely to live in rural areas as compared to non-Aboriginals (\cite{survey}\cite{Withrow_2016}), distance to radiotherapy likely plays an important role in influencing access to cancer treatment, including radiotherapy, on top of the other disadvantages this population already faces. However, there is currently a lack of information with regards to the role of distance to radiotherapy centre on cancer outcomes, particularly in the context of indigenous populations. In this study, then, we sought to describe cancer outcomes among the indigenous populations in Canada on a national level, and explore the impact of potential associated variables, including distance to radiotherapy and other sociodemographic variables.