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Cancer incidence and survival among Métis adults in Canada: Results from the Canadian census follow-up cohort (1992-2009)

TitleCancer incidence and survival among Métis adults in Canada: Results from the Canadian census follow-up cohort (1992-2009)
Year of Publication2018
AuthorsMazereeuw, M. V., Withrow D. R., E. Nishri D., Tjepkema M., Vides E., and Marrett L. D.
PagesE320 - E326

BACKGROUND: Métis people are 1 of 3 Aboriginal groups recognized by the Canadian constitution. We estimated site-specific incidence rates and survival for the most common cancers among Métis adults in Canada and compared these with rates among non-Aboriginal adults in Canada. METHODS: We examined responses to the 1991 long-form census, including self-reported Métis ancestry linked to national mortality and cancer databases for followup from 1992 to 2009. We estimated age-standardized incidence rates and 5-year relative survival. We determined relative risk (RR) of cancer among Métis and non-Aboriginal adults using Poisson regression, and estimated excess mortality rate ratios using ethnicity-specific life tables. RESULTS: For all cancers and both sexes combined, cancer incidence was similar for Métis and non-Aboriginal adults. However, incidence was significantly higher among Métis adults than among non-Aboriginal adults for the following cancers: female breast (RR 1.18, 95% confidence interval [CI] 1.02-1.37), lung (RR 1.34, 95% CI 1.18-1.52), liver (RR 2.09, 95% CI 1.30-3.38), larynx (RR 1.60, 95% CI 1.03-2.48), gallbladder (RR 2.35, 95% CI 1.12-4.96) and cervix (RR 1.84, 95% CI 1.23-2.76). Métis people had poorer survival for prostate cancer (excess mortality rate ratio 2.60, 95% CI 1.52-4.46). INTERPRETATION: We found higher incidence for several cancers and poorer survival after prostate cancer among Métis adults. Several of these disparities may be related to lifestyle factors (including tobacco use, obesity and lack of cancer screening), providing evidence to support development of public health policy and health care to address cancer burden in the Métis people of Canada. Métis people are 1 of the 3 distinct groups named in the Constitution Act of 1982 as the "aboriginal peoples of Canada," explicitly defined as "Indian [now referred to as 'First Nations'], Inuit, and Métis peoples of Canada." Aboriginal peoples in Canada experience greater poverty and unemployment, lower levels of education and higher prevalence of several known risk factors for chronic disease (tobacco smoking, obesity and unhealthy diet) relative to non-Aboriginal Canadians. These diverse influences and disadvantages have ultimately resulted in poorer health outcomes, such as lower life expectancy and higher prevalences of chronic conditions. The lack of racial or ethnic identifiers in Canadian health databases, including cancer registries, has limited our ability to accurately determine and effectively address priorities for chronic disease prevention in these populations. The Métis people of Canada are descendants of the offspring of early unions between First Nations women and European fur traders. Subsequent intermarriage of these mixed-ancestry individuals led to the genesis of a new Aboriginal people - the Métis people - with their own unique culture, traditions, language (Michif), way of life, collective consciousness and nationhood (the Métis Nation). Métis constitute 1.4% of the Canadian population, numbering over 450 000 individuals who are dispersed across the country, with particular concentrations in Ontario and the Prairie provinces. The paucity of formal national registration systems for Métis, coupled with the fact that Métis people tend not to cluster in specific geographic areas (unlike many Inuit and First Nation communities), has contributed to underrepresentation of Métis in the health literature relative to their share of the population. Furthermore, no single definition of Métis exists, which often makes comparisons between studies and generalization of results challenging. National data about cancer incidence among Métis are lacking, and Métis-specific cancer survival has never been estimated. Three provincial-level studies of cancer incidence among Métis in Canada had too few cases to produce precise estimates of differences between Métis people and the general population. We examined patterns of site-specific cancer incidence and survival among Métis people in Canada from 1992 to 2009 and evaluated their risk relative to the non-Aboriginal population.

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