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Overdiagnosis accounts for increased thyroid cancer incidence
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The incidence of thyroid cancer worldwide has consistently been increasing in recent decades and may be attributable to the use of new diagnostic techniques coupled with increased medical surveillance and access to health care services, according to a perspective published in The New England Journal of Medicine.
However, no substantial change in thyroid cancer-related mortality has been observed despite rising incidence, according to Salvatore Vaccarella, PhD, of the International Agency for Research on Cancer in Lyon, France, and colleagues.
Vaccarella and colleagues calculated the number of overdiagnosed cases of thyroid cancer in 12 countries — Australia, Denmark, England, Finland, France, Italy, Japan, Norway, South Korea, Scotland, Sweden and the United States — using data from the International Agency for Research on Cancer’s reference publication Cancer Incidence in Five Continents.
“Countries such as the [United States], Italy and France have been most severely affected by overdiagnosis of thyroid cancer since the 1980s, after the introduction of ultrasonography, but the most recent and striking example is the Republic of Korea,” Vaccarella said in a press release. “A few years after ultrasonography of the thyroid gland started being widely offered in the framework of a population-based multi-cancer screening, thyroid cancer has become the most commonly diagnosed cancer in women in the Republic of Korea, with approximately 90% of cases in 2003 to 2007 estimated to be due to overdiagnosis.”
Researchers conclude that overdiagnosed cases in women from 2003 to 2007 account for 70% to 80% of cases in the United States, Italy, France and Australia and 50% of cases in Japan, the Nordic countries, England and Scotland. Overdiagnosis in men for the same period accounted for 70% of cases in France, Italy and South Korea, 45% in the United States and Australia and less than 25% in the other countries evaluated.
“More than half a million people are estimated to have been overdiagnosed with thyroid cancer in the 12 countries studied,” Christopher P. Wild, PhD, director of the International Agency for Research on Cancer, said in the release. “The drastic increase in overdiagnosis and overtreatment of thyroid cancer is already a serious public health concern in many high-income countries, with worrying signs of the same trend in low- and middle-income countries. It is, therefore, critical to have more research evidence in order to evaluate the best approach to address the epidemic of thyroid cancer and to avoid unnecessary harm to patients.” – by Amber Cox
Disclosure: The researchers report no relevant financial disclosures.
Perspective
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Christian Nasr
This study provides yet another piece of evidence that screening for thyroid cancer in the general population is absolutely not justified. South Korean thyroid specialists discovered this after the national screening program led to a massive increase in finding asymptomatic thyroid cancer cases. Years later, that group figured out that patients with small tumors that would not have come to medical attention otherwise, when managed conservatively — either through monitoring without resection or less-aggressive treatment, such as partial thyroid surgery, no radioactive iodine treatment — were associated with normal survival and low recurrence rate, similar to more-aggressive modalities. Thus, those patients would have been better off not having the tumors discovered in the first place.
The increased incidence in other wealthy countries can be explained by the incidental discovery of clinically impalpable tumors through the increased use of more sophisticated imaging modalities. While this accounts for the majority of excess cases of thyroid cancer, there has been a real increase in large tumors that come to attention through neck examination. This latter increase has been more difficult to explain, and it may have to do with environmental factors.
It is important to realize that while papillary thyroid cancer accounts for the excess cases, the incidence of the other types of thyroid malignancy (follicular, medullary and anaplastic) has not seen a significant increase. Since one cannot definitely predict which cancer will be indolent and which will be aggressive, when a thyroid nodule is identified, guidelines put forth by thyroid experts should be considered for the work-up. No nodule, no matter the size, should be completely ignored, and the majority of nodules deserve to be followed to document stability either clinically or with imaging.
Disclosure: Nasr reports serving as a speaker for Sanofi USA.
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