Thyroid cancer today: epidemiology and scenario

In the past 20-30 years, the epidemiology of thyroid nodular disease has changed remarkably owing to a striking increase in the number of thyroid nodules being diagnosed in the adult population.

In Italy, approximately 50% of all adults have one or more thyroid nodules, and the figure climbs as high as 75% in certain regions (1). The increasing prevalence of nodules is accompanied by a similar trend in thyroid cancer rates.

The increase is more marked in women than in men (8.1% versus 6.2% per year, respectively) (3). The same basic trend can be observed in other countries as well. (The exception is Sweden, where the incidence of thyroid cancer in both sexes has dropped by 18%). On the whole, however, is the exception: although in the geographic variability of the phenomenon with an average global increase of 58.1% with the exception of Sweden where a decrease of 18% is recorded for both genders (4).

The increase in thyroid cancer is due in large part to the diagnosis of localized, non-aggressive tumors. However, there are already signs of a parallel rise in the incidence of larger and more aggressive cancers, with local spread or even distant metastases at the time of diagnosis (5).

The incidence of tumours with diameters of > 6 cm has more than doubled (6). Thyroid cancer mortality rates are also showing a tendency to increase. In the past 15 years, rates in the United States have increased by about 0.8% per year (2). Today, thyroid cancer represents the fifth most frequent tumour in women in the United States. The increased incidence of thyroid cancer can be explained in part by the increasingly widespread use of modern diagnostic imaging technology and histopathological analysis (6).

The scenario in Italy
Italy is one of countries that have experienced the most marked increases in thyroid cancer incidence (7), with a predominance of papillary thyroid cancers and similar distributions in males and females (8). Incidence rates vary widely from region to region: between 2001 and 2005, the highest figures were recorded in Emilia-Romagna, in the province of Ferrara (37.5/100,000); the lowest were in Trentino Alto Adige (7.3/100,000) (8).

These differences have been attributed by some to regional differences in access to the health system, but roles have also been proposed for environmental factors (9).

The main environmental risk factor for thyroid cancer is exposure to ionizing radiation, especially during childhood (10). This exposure can be occupational or caused by atomic accidents. However, some studies suggest that the risk of thyroid cancer can also be increased by radiation exposure related to diagnostic tests (11) or to the natural radioactivity linked to peculiar geological factors (e.g., volcanic soil, geothermal areas) (9).

Iodine deficiency plays a major role in the pathogenesis of simple and nodular goitres, as shown by their decreased prevalence after the implementation of iodine supplementation campaigns (12). However, the relation between iodine deficiency and the incidence of thyroid cancer remains controversial.

The risk of thyroid cancer is more closely linked to genetic factors than that of any other tumour (13). Genetic and epigenetic factors and the iteration between these are involved in the carcinogenesis of benign nodules and carcinomas and influence tumoral aggressiveness (14). A different genetic substratum in the different populations (15) could contribute to the epidemiological heterogeneousness observed in the world. The genetic make-up could also represent the predisposing terrain on which environmental factors act.

Therefore, to provide “personalized therapy” for thyroid cancers, each patient has to be “profiled” from multiple points of view, identifying the diverse factors–environmental, genetic, epigenetic, nutritional, and socioeconomic to name a few—that may have contributed to the disease and/or are likely to affect its treatment.

Nonuniform distribution of resources and technology can also contribute to differences in the management of thyroid cancer, hindering widespread application of internationally recommended clinical protocols in daily practice.

The continuous interaction of all these elements yields a complex phenomenon, whose optimal management requires balanced collaboration by all parties involved (specialists and general practitioners, patients and their associations, the healthcare institutions). Diagnostic and therapeutic innovations can be an invaluable resource, but their indiscriminate use can increase healthcare costs without necessarily improving the quality of care.


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