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Ontario Cancer Facts

Female thyroid cancer incidence varies across geographic regions in Ontario

Jul 2018

Highlights

 

  • There is substantial geographic variation in female thyroid cancer incidence across Ontario, with the highest rates in and around the Greater Toronto Area.
  • Thyroid cancer incidence has been increasing in Ontario over the past two decades.
  • Increases may be partially due to better diagnostic technology, which may allow for the detection of sub-clinical tumours.

 

A recent analysis found that thyroid cancer incidence rates in females varied greatly among census divisions (CDs) in Ontario from 1999 to 2013. Overall, the CDs surrounding and including Toronto (Peel, Halton, Toronto and York) had the highest rates during this time period, and rapidly increasing rates were observed in northeastern and southwestern Ontario, especially in Algoma, Cochrane, Chatham-Kent and Essex.

In 1999–2003, the age-standardized incidence rate (ASIR) for females ranged across CDs from 7.4 per 100,000 in the combined Lennox and Addington, Frontenac and Renfrew to 32.1 per 100,000 in York. For the 5 most recent years of the analysis, 2009 to 2013, ASIRs ranged from a high of 68.1 per 100,000 in Algoma to a low of 13.2 per 100,00 in the combined Prescott and Russell, Stormont, Dundas and Glengarry CDs.

Age-standardized incidence rates (ASIR) for thyroid cancer in Ontario women age 20 and older, by census division

Female thyroid cancer ASIR (1999 to 2003) Map
Female thyroid cancer ASIR (2009 to 2013) Map

 

 

Data source: Ontario Cancer Registry (November 2016), CCO

 

Notes:

  1. Rates are per 100,000 and age-standardized to the 2011 Canadian population.
  2. Thyroid cancer (ICD-O-3 C73.9 excluding histologies 9050-9055, 9140, 9590-9992).
  3. Multiple primaries were excluded from this analysis.
  4. For CDs with small cell counts, their counts were combined with neighbouring CDs so that rates could be displayed.

 

Age-standardized thyroid cancer incidence in Ontario women age 20 and older, by census division (CD)

Census division (CD) ASIR for 1999 to 2003 ASIR for 2009 to 2013
Algoma 17.9 68.1
Brant 9.3 17.5
Bruce and Huron combined 27.4 30.4
Chatham-Kent 10.8 38.2
Cochrane 21.4 55.7
Durham 22.8 51.8
Elgin and Oxford combined 19.6 25.1
Essex 10.9 43.7
Grey and Dufferin combined 17.8 29.6
Haldimand-Norfolk 13.8 24.4
Haliburton and Kawartha Lakes combined 20.4 24.9
Halton 20.4 55.2
Hamilton 10.6 20.7
Hastings 15.1 15.8
Kenora, Rainy River, and Thunder Bay combined 13.2 34.8
Lambton 18.0 26.2
Leeds and Grenville, and Lanark combined 9.8 13.4
Lennox and Addington, Frontenac, and Renfrew combined 7.4 15.2
Middlesex 20.8 33.0
Niagara 14.3 22.4
Northumberland and Prince Edward combined 11.9 29.1
Ottawa 13.8 22.4
Parry Sound and Muskoka combined 20.0 35.7
Peel 25.4 49.6
Perth 21.0 30.7
Peterborough 22.7 32.1
Prescott and Russell, Stormont, Dundas and Glengarry combined 9.2 13.2
Simcoe 19.6 34.0
Sudbury and Manitoulin combined 14.9 20.6
Timiskaming and Nipissing combined 11.0 22.8
Toronto 32.0 64.3
Waterloo 21.8 35.4
Wellington 17.5 34.0
York 32.1 63.6

Data source: Ontario Cancer Registry (November 2016), CCO

Notes:

  1. Rates are per 100,000 and age-standardized to the 2011 Canadian population.
  2. Thyroid cancer (ICD-O-3 C73.9 excluding histologies 9050-9055, 9140, 9590-9992).
  3. Multiple primaries were excluded from this analysis.
  4. For CDs with small cell counts, their counts were combined with neighbouring CDs so that rates could be displayed.

Similar to the pattern observed for all-stage thyroid cancer incidence, the CDs surrounding and including Toronto (Peel, Durham, Halton, York and Toronto) had the highest ASIR for early-stage thyroid cancer. Thyroid cancer was more likely to be diagnosed at stage 1 with approximately three-quarters of cases in 2013 diagnosed at this early stage. Only 5% of thyroid cancer cases were diagnosed at stage 4.

There was a rapid increase in thyroid cancer incidence throughout the province, between 1999–2003 and 2009–2013, with increases in incidence observed in every CD in Ontario. The rising incidence rate of thyroid cancer has been linked to improved diagnostic technology, including the use of ultrasound and fine-needle aspiration, which may have allowed for the detection of subclinical tumours. This association has been observed in Ontario, where there are large differences across the province in the use of discretionary medical tests, including diagnostic ultrasound, and the CDs corresponding to the regions with the highest test use were also the CDs with the highest incidence.

Unlike most common cancers, thyroid cancer incidence is higher in females than in males. A number of possible reasons for this higher incidence in females have been proposed in the literature. Males and females have biological differences in their hormone levels, including thyroid stimulated hormone and sex steroids, so females are more likely to have thyroid disease due to higher hormone levels. Additionally, females seek medical attention more often than males and participate more actively in medical visits, which means they are more likely to get diagnosed.

 

Healthcare providers and policy-makers must consider the treatment implications and possible long-terms effects of the rising burden of thyroid cancer as they engage in planning for the healthcare system and patients, especially for people diagnosed at an early stage.

References

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