The rates of diagnosis of thyroid cancer varied up to 4 times across the geographic regions of Ontario: study

The dramatic increase in the incidence rates of thyroid cancer in women contributes to it being the fastest growing cancer type in North America today.  The differences in access to or use of medical diagnostic tests by more educated, urban and healthier patient populations is driving the increasing incidence of thyroid cancer according to research conducted at the Institute for Clinical Evaluative Sciences (ICES) Queen’s and Queen’s Cancer Research Institute.

The study, published in Cancer Medicine, found the regions with the highest use of discretionary medical tests (pelvic ultrasound, abdominal ultrasound, echocardiogram, resting electrocardiogram, cardiac nuclear perfusion tests and bone scan); highest population density and better education had the highest rates of thyroid cancer diagnoses.  

“Differences in the rates of the ordering of discretionary diagnostic medical tests, such as diagnostic ultrasound, in different geographic regions of Ontario lead to differences in the rates of thyroid cancer,”  says lead author Stephen Hall, adjunct scientist at ICES Queen’s, an Otolaryngologist/Head and Neck Surgeon at Queen’s University and a clinician scientist at the Queen’s Cancer Research Institute.  

The population-based, retrospective study of 12,959 patients with thyroid cancer between January 2000 and December 2008 in Ontario found:  

• An overall 112 per cent increase in the numbers of new cases (893 to 1890) over the nine years across Ontario.
• Eighty per cent of patients were female.
• The rate of diagnosis (cases/100,000/year) varied by LHIN from 21.56 to 5.22 (mean 11.49) over the nine years. 
• LHINs with the higher rates of diagnosis had highest use of diagnostic ultrasound of neck as well as pelvis and abdomen.
• LHINs with the higher rates of diagnosis were urban with higher rates of education and higher income.   

“Overdiagnosis occurs when a condition is diagnosed that would otherwise not go on to cause symptoms or death and includes non-progressive or very slow growing cancers. Thyroid cancer fulfills the criteria for overdiagnosis and, given the increasing caseload, thyroid oncologists ought to be considering the clinical relevance of some cases,” says Hall. Further research is required to identify reasons for variations in ordering of tests.  

The study “Access, excess and overdiagnosis: the increasing incidence of thyroid cancer,” was published in Cancer Medicine.  

Authors: Stephen F Hall, Jonathan Irish and Patti Groome.  

ICES is an independent, non-profit organization that uses population-based health information to produce knowledge on a broad range of healthcare issues. Our unbiased evidence provides measures of health system performance, a clearer understanding of the shifting healthcare needs of Ontarians, and a stimulus for discussion of practical solutions to optimize scarce resources. ICES knowledge is highly regarded in Canada and abroad, and is widely used by government, hospitals, planners, and practitioners to make decisions about care delivery and to develop policy.  

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