Temporal Trends for Thyroid Carcinoma in Australia: An Increasing Incidence of Papillary Thyroid Carcinoma (1982–1997)

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Abstract
The incidence of papillary thyroid carcinoma (PTC) has increased in many countries over the past 60 years. In Tasmania (an island state of the Australian Commonwealth with a well-documented history of iodine deficiency, subsequent supplementation and more recently a return to deficiency), there has been a fourfold rise in PTC incidence over the past two decades. The aim of this study was to evaluate thyroid carcinoma (TC) incidence trends in Australia, with particular reference to the roles of iodine nutrition, ionizing radiation, and ascertainment bias. Data from Australia's regional cancer registries were used to determine national TC incidence and mortality trends for the period 1982-1997. There were 9,053 new diagnoses of TC. Papillary, follicular, medullary, anaplastic, and "other diagnoses," accounted for 65.8%, 17.8%, 4.6%, 1.3%, and 10.5% of registered cases, respectively. TC incidence rates increased by 6.7% per year for females and 4.4% per year for males between 1982-1997 (p < 0.001). The increase was primarily because of a 10.7% per year and 8.3% per year rise in PTC incidence for females and males respectively (p < 0.001). The increase in PTC incidence was most significant for the population residing on Australia's eastern seaboard. The greatest relative and absolute increase in PTC (24.7% per year) occurred in Tasmania. These findings are consistent with a true increase in underlying PTC incidence rates. A link between current incidence trends and past iodine deficiency/radioiodine exposure during the 1950s and early 1960s is possible.