Abstract
In North America, the incidence of thyroid cancer is increasing by over 6% per year. We studied the trends and factors influencing thyroid cancer incidence, its clinical presentation, and treatment outcome during 1970–2010 in a population-based cohort of 2306 consecutive thyroid cancers in Canada, that was followed up for a median period of 10.5 years. Disease-specific survival (DSS) and disease-free survival were estimated by the Kaplan–Meier method and the independent influence of various prognostic factors was evaluated by Cox proportional hazard models. Cumulative incidence of deaths resulting from thyroid cancer was calculated by competing risk analysis. A P-value <0.05 was considered to indicate statistical significance. The age standardized incidence of thyroid cancer by direct method increased from 2.52/100,000 (1970) to 9.37/100,000 (2010). Age at diagnosis, gender distribution, tumor size, and initial tumor stage did not change significantly during this period. The proportion of papillary thyroid cancers increased significantly (P < 0.001) from 58% (1970–1980) to 85.9% (2000–2010) while that of anaplastic cancer fell from 5.7% to 2.1% (P < 0.001). Ten-year DSS improved from 85.4% to 95.6%, and was adversely influenced by anaplastic histology (hazard ratio [HR] = 8.7; P < 0.001), male gender (HR = 1.8; P = 0.001), TNM stage IV (HR = 8.4; P = 0.001), incomplete surgical resection (HR = 2.4; P = 0.002), and age at diagnosis (HR = 1.05 per year; P < 0.001). There was a 373% increase in the incidence of thyroid cancer in Manitoba with a marked improvement in the thyroid cancer-specific survival that was independent of changes in patient demographics, tumor stage, or treatment practices, and is largely attributed to the declining proportion of anaplastic thyroid cancers.This article shows there is an increase in the incidence of thyroid cancers of all sizes in a population cohort in Canada. The improvement in thyroid cancer survival is due to reduced proportion of anaplastic thyroid cancer.
Highlights
Thyroid cancer is the most common malignant endocrine tumor and is the seventh most common cancer seen in Canadians with an estimated 5650 new thyroid cancers diagnosed in 2012 [1]
Cancer Medicine published by John Wiley & Sons Ltd
The age standardized incidence rate (ASIR) per 100,000 for anaplastic thyroid cancers fell from 0.11 during 1970–1980 to 0.05 in 2001–2010 for both sexes and the respective rates for papillary thyroid cancer went up from 0.93 to 6.64
Summary
Thyroid cancer is the most common malignant endocrine tumor and is the seventh most common cancer seen in Canadians with an estimated 5650 new thyroid cancers diagnosed in 2012 [1]. In Canada, the incidence of thyroid cancer is increasing more rapidly than any other cancer; by 6.8% per year in Canadian males (1998–2007) and by 6.9% per year in Canadian females (2002–2007) [1]. The age standardized incidence rate (ASIR) of thyroid cancer per 100,000 Canadians has increased from 1.1 in 1970–1972 to 6.1 in 2012 for males, and from. The trends in the United States (US) mirror that of Canada with a threefold increase in the incidence of thyroid cancer from 4.85/100,000 in 1975 to 14.25/100,000 in 2009 and an annual percent increase (2000–2009) of 6.0% for the US males and 6.9% for the US females [15]. The age and delay adjusted incidence rate of thyroid cancer between 2006 and 2010 was 6.1/100,000 for the US males and 18.2/100,000 for the US females using joint point regression program.
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