Population-Based Differences in Cancer Incidence between Immigrants and Non-Immigrants in Canada from 1992-2015

Abstract

The purpose of this study was to investigate if there are differences in cancer incidence between immigrants and non-immigrants in Canada. We hypothesized that immigrants have lower cancer incidence compared to non-immigrants. In this retrospective study, a linked-database approach was employed using Statistics Canada data. The Canadian Cancer Registry and Canadian Vital Statistics Database were linked with the 1991 Census cohort and the cohort was followed from 1992-2015 for cancer incidence. Excluded persons included Census non-respondents, institutional residents, those living on reserves and those less than 25 years of age. Sampling and bootstrap weights were used to ensure the sample represented the Canadian population and for statistical analyses. Total unweighted and weighted sample was 2,585,160 and 17,002,560, respectively which provided adequate power to answer the research question. Multivariate logistic regression and cox regression models included age, sex, household income, marital status, highest degree of education, knowledge of Canada's official languages (English or French), immigrant status and region of birth. Subcategories of immigrants were created based on time spent in Canada (0-4, 5-9, 10-19, 20+ years). Raw data showed that 16.8% of immigrants and 15.9% of non-immigrants had cancer. After adjusting, logistic regression analyses showed that immigrants had lower odds of any cancer diagnoses in comparison with non-immigrants (OR = 0.92, 95% CI [0.92,0.93], p<.001), as well as lung (OR = 0.74, 95% CI [0.72-0.75], p<.001); breast (OR = 0.96, 95% CI [0.94-0.98], p = .001); colorectal (OR = 0.93, 95% CI [0.91-0.95], p<.001) and head and neck cancer (OR = 0.85, 95% CI [0.81-0.90], p<.001). However, immigrants had higher odds of stomach cancer and non-cervix gynecological cancers (OR = 1.39, 95% CI [1.32-1.46]; OR = 1.06, 95% CI [1.02-1.10]), respectively. Hazard ratios were lower for immigrants in comparison to the Canadian-born but increased based on time spent in Canada (0-4 years: 0.77, 95% CI [0.71-0.84], p<.001; 5-9 years: 0.82, 95% CI [0.75-0.89], p<.001; 10-19 years: 0.90, 95% CI [0.82-0.98], p = .011). This study demonstrates a significant difference in cancer incidence between immigrants and non-immigrants. These results support current research in the observation of a 'healthy immigrant effect' (HIE) which convey that immigrants have better health outcomes than their native-born counterparts, with the effect decreasing over time spent in the host country. Since we controlled for demographic and socio-economic factors, we propose other factors to be contributing to the HIE such as individual-level health behaviors including smoking, diet and access to screening services. While it points to a HIE, we propose this phenomenon to be more complex due to the possibility of under-reporting of cases or differences in health behaviors, warranting further studies in this area.