Disparities In Cancer Incidence Between Indigenous And Non-Indigenous Adults In Canada: Results From Linkage Of The 1991 Census Mortality Cohort And The Canadian Cancer Registry

Maegan PRUMMEL, Cancer Care Ontario, Canada
PRUMMEL M. 1 , MARRETT L. 1,2 , WITHROW D. 1,2 , NISHRI D. 1 , TJEPKEMA M. 3

1 Cancer Care Ontario, Aboriginal Cancer Control Unit
2 University of Toronto, Dalla Lana School of Public Health
3 Statistics Canada, Health Analysis Division

Purpose: Canada has three constitutionally recognized Aboriginal groups: First Nations (FN), Inuit, and Métis, comprising 4.3% of the population. Ethnicity is not routinely collected in Canadian cancer registries so periodic studies using different methodologies are needed. This linkage provided an opportunity to examine cancer incidence in Canada’s two largest indigenous groups, FN and Métis.
Methods: Respondents aged 25+ to the 1991 Long Form Census were matched with national cancer registry and mortality databases and followed from 1992-2009. Three cohorts were identified: FN (N~=62,000; 5,000 cancers), Métis (N~=11,000; 1,000 cancers) and non-Aboriginal (N~=2,653,000; 336,000 cancers). Incidence rates were estimated for common cancers, age-standardized to the World Standard population. Relative risk (RR) of cancer in FN or Métis was assessed compared to non-Aboriginal adults, adjusting for age, income and rurality.
Results: Compared to non-Aboriginal adults, FN had significantly lower incidence of prostate (RR=0.79, 95%CI=0.73-0.86), male lung (RR=0.79, 95%CI=0.72-0.87) and female breast cancers (RR=0.92, 95%CI=0.86-0.99), yet significantly higher incidence of colorectal (men:RR=1.15, 95%CI=1.04-1.26; women:RR=1.29, 95%CI=1.17-1.42), kidney (men:RR=1.65, 95%CI=1.41-1.93; women:RR=1.99, 95%CI=1.67-2.36), and cervical cancers RR=2.00, 95%CI=1.70-2.36). Métis had significantly higher incidence than non-Aboriginal adults for female breast (RR=1.18, 95%CI=1.02-1.37), lung (men:RR=1.22, 95%CI=1.03-1.43; women:RR=1.56, 95%CI=1.28-1.89), and cervical cancers (RR=1.84, 95%CI=1.23-2.76), and significantly lower incidence of female colorectal cancer (RR=0.69, 95%CI=0.50-0.95).  
Conclusions: Indigenous people in Canada experience higher incidence of several cancers, supporting the need for: 1. additional research to understand why; 2. additional investment in prevention to reduce current and future burden in a wholistic and culturally appropriate manner; and 3. creation of databases for ongoing monitoring of cancer burden. Doing so will require application of novel methodologies and appropriate data sharing, collaboration and capacity-building arrangements with Indigenous organizations.
Funding source: Canadian Institutes of Health Research