Abstract

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Background

Thyroid cancer incidence in Canada has increased rapidly over the past 25 years. This study examines thyroid cancer incidence and relative risk according to individual-level sociodemographic characteristics in two population-based cohorts.

Methods

The analysis uses data from the 1991 and 2001 Canadian Census Health and Environment Cohorts (CanCHECs). Using nine years of cancer follow-up for both time periods, age-standardized incidence rates of thyroid cancer were estimated by sex—with sex-specific estimates produced by immigrant status, ethnicity, educational attainment and family income—and by histology type. All characteristics were included in sex-specific standard Cox proportional hazard models to examine the relative risk of thyroid cancer and the relative risk of papillary versus non-papillary thyroid cancer.

Results

A significant increase over time in thyroid cancer incidence was observed for both sexes, and across all characteristics. Immigrant status and ethnicity were each independently associated with the risk of thyroid cancer, with immigrant men and women and East and Southeast Asian women at higher risk. Men and women who had a postsecondary diploma or higher or who were in the highest income quintile were at increased risk of being diagnosed with papillary thyroid cancer, but not with non-papillary thyroid cancer.

Interpretation

While increased detection has played a role in the rising incidence of thyroid cancer in Canada, it does not fully account for the greater relative risk among the immigrant population and certain ethnic groups. More research is needed to better understand the determinants of the increased risk in these populations.

Keywords

thyroid cancer; incidence; risk; cohort studies; sociodemographic

Findings

Thyroid cancer incidence in Canada has increased rapidly over the past 25 years. The age-standardized incidence rate for women has increased five-fold to a projected 29.1 per 100,000 in 2017. At the same time, there has been a four-fold projected increase for men to 8.8 per 100,000.1 Although the increased risk in women has been widely reported, studies in the United States and England have also found variations in risk according to sociodemographic characteristics such as ethnicity, education and income. In Canada, the examination of these associations has been limited to provincial-level data only or area-based measures, as little information on these characteristics has been available at the national level. [Full Text]

Authors

Tracey Bushnik (tracey.bushnik@canada.ca) is with the Health Analysis Division at Statistics Canada, Ottawa, Ontario. William K. Evans is Professor Emeritus in the Department of Oncology, McMaster University, Hamilton, Ontario.

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