Abstract
Introduction: Income, a component of socioeconomic status, influences cancer risk as a social determinant of health. We evaluated the independent effects of individual- and area-level income on site-specific cancer incidence in Canada.
Methods: We used data from the 2006 and 2011 Canadian Census Health and Environment Cohorts (CanCHECs) which are probabilistically linked datasets constituted by 5.9 million and 6.5 million respondents of the 2006 Canadian long-form census and 2011 National Household Survey, respectively. Individuals were linked to the Canadian Cancer Registry through 2015. Individual-level income was derived using after-tax household income adjusted for household size. Annual tax return postal codes were used to assign area-level household income quintiles to individuals for each year of follow-up. We calculated age-standardized incidence rates (ASIR) and rate ratios for cancers overall and by site. We conducted multivariable negative binomial regression to adjust these rates for other demographic and socioeconomic variables.
Results: Individuals of lower individual- and area-level income had higher ASIRs compared to those in the wealthiest income quintile for head and neck, oropharyngeal, esophageal, stomach, colorectal, anal, liver, pancreas, lung, cervical, and kidney and renal pelvis cancers. Conversely, higher individual- and area-level income individuals had higher ASIRs for melanoma, leukemia, Hodgkin’s lymphoma, and non-Hodgkin’s lymphoma, breast, uterine, prostate, and testicular cancers. Differences in site-specific incidence by income quintile remained after adjustment for other socioeconomic variables.
Conclusions: Although Canada’s publicly funded healthcare system provides universal coverage, inequalities in cancer incidence persist across individual- and area-level income gradients. Individual- and area-level income affect cancer incidence through independent mechanisms.