Abstract

Background

Age-standardized incidence rates (ASIRs) of thyroid cancer (TC) have increased in many parts of the world, primarily because of increased papillary TC detection. While rapid increases in TC incidence have also been reported in Canada, an analysis of incidence and survival by histologic subtype has been lacking. Moreover, recent data points in Canada suggest that the era of rapid annual increases may have ended.

Data and methods

Data are from the Canadian Cancer Registry, the Canadian Vital Statistics–Death Database and an analytic file linking the two. Annual percent changes (APCs) in incidence and mortality rates are estimated using Joinpoint regression. Net survival (NS) is derived using the Pohar Perme estimator.

Results

Among females, TC ASIRs decreased by 3.0% annually from 2012 to 2016, following years of rapid growth. Among males, a long period of rapid increase ended in 2012 with no subsequent decline. For both sexes the overall incidence trend was driven by changes over time in papillary TC and incidence trends in non-papillary TC varied significantly. From 1992 to 2016, TC mortality rates were stable among females and increased slightly among males (APC = 1.2). Five-year NS was higher among papillary cases (99%) than among non-papillary cases (80%) and among females (99%) than among males (94%). Overall, five-year NS increased by 2.1 percentage points from the period from 1992 to 1996 to the period from 2010 to 2014.

Interpretation

The results of this study confirm the central role of papillary TC cases in TC incidence and survival trends in Canada. Given recent changes in trend and TC management guidelines, projected increases in TC rates after 2016 could be re-examined.

Keywords

histology, incidence, mortality, net survival, registries, Joinpoint regression analysis, population-based study, survival analysis, thyroid neoplasms, trends

DOI: https://www.doi.org/10.25318/82-003-x202000100002-eng

Findings

In Canada, thyroid cancer (TC) was the fifth most frequently diagnosed cancer among females in 2016, behind breast, lung and bronchus, colorectal and uterine cancers. Among males, it was the 13th most commonly diagnosed cancer. However, TC mortality is only a small fraction of incidence because of the generally excellent prognosis for this disease. Until 2012, rapid increases in TC incidence in Canada had been observed and attributed to overdiagnosis of clinically unimportant lesions detected by modern imaging. Both short- and long-term projections indicate continued increases in incidence. [Full article]

Authors

Larry F. Ellison (larry.ellison@canada.ca) is with the Centre for Population Health Data at Statistics Canada, Ottawa, Ontario. Tracey Bushnik (tracey.bushnik@canada.ca) is with the Health Analysis Division at Statistics Canada, Ottawa, Ontario.

Start of text box

 

What is already known on this subject?

  • Age-standardized incidence rates (ASIRs) of thyroid cancer (TC) have increased in many parts of the world, primarily because of increased papillary TC detection.
  • Until 2012, rapid increases in TC ASIRs in Canada had been observed and attributed to overdiagnosis of clinically unimportant lesions detected by modern imaging.
  • The five-year survival prognosis for TC in Canada is generally excellent and results in mortality rates that are only a small fraction of corresponding incidence rates.

What does this study add?

  • Papillary TC cases constitute 93% of TC cases diagnosed in Canada.
  • In Canada, TC ASIRs declined for females and stabilized for males from 2012 to 2016.
  • The shift in trend is primarily due to changes in papillary TC incidence that were not observed for non-papillary TC cases. The sex-specific age groups most affected by the shift were those that previously experienced the largest increases in TC rates.
  • Overall, age-standardized mortality rates remained stable from 1992 to 2016, but increased slightly among males.
  • The prognosis after a TC diagnosis in Canada is considerably influenced by the histology of the cancer—prognosis for papillary TC is excellent, but it is very poor for the anaplastic subtype.
  • Five-year net survival for TC in Canada has increased slightly since the early 1990s.

End of text box

Date modified: