Global patterns of the incidence of thyroid cancer in children and adolescents closely correspond to the increases seen in recent decades in adults. The patterns point to the same culprit in both groups – overdiagnosis. The finding underscores recommendations to limit screening.
“Our findings suggest that recommendations against screening for thyroid cancer in the asymptomatic adult population who are free from risk factors should be extended to explicitly recommend against screening for thyroid cancer in similar populations of children and adolescents,” say the authors, led by Salvatore Vaccarella, PhD, of the International Agency for Research on Cancer, in Lyon, France.
The study was published online Jan. 19 in The Lancet Diabetes and Endocrinology.
In an accompanying comment, Livia Lamartina and colleagues from the department of nuclear medicine and endocrine oncology, Institut Gustave Roussy and the University Paris-Saclay, Villejuif, France, emphasize that unnecessary screening of thyroid cancer in children can have substantial implications.
“Overdiagnosis might transform a child into a thyroid cancer patient for the rest of their life, and overtreatment might induce complications and possibly lead to the requirement of lifelong thyroid hormone treatment,” they write.
“Therefore, screening with ultrasonography should not be recommended in asymptomatic children and adolescents,” they conclude.
Study findings
For the study, Dr. Vaccarella and colleagues evaluated the incidence of thyroid cancer in 49 countries and territories and mortality in 27 countries, using the most up-to-date data from the International Incidence of Childhood Cancer Volume 3 study, the Cancer in Five Continents database, and the World Health Organization mortality database.
Although there was considerable variability between countries, the incidence of thyroid cancer in children and adolescents aged 0-19 years increased rapidly between 1998 and 2002 and again between 2008 and 2012 in nearly all countries.
Country-specific incidence rates strongly correlated with rates in adults (r > 0.8), including the temporal aspects of the incidence rates (r > .0.6).
Of the 8049 thyroid cancers that were detected, 6935 (86.2%) were papillary carcinomas, 682 (8.5%) were follicular carcinomas, and 307 (3.8%) were medullary carcinomas, as determined on the basis of the WHO classification of thyroid carcinomas. Sixty-four tumors (0.8%) were of unspecified subtype. As is commonly observed in adults, rates were higher in girls than in boys and increased with older age for both sexes.
The strong correlation between children and adults in the timing of the increases in incidence was especially notable in countries where overdiagnosis has been identified as having a major role in the increasing thyroid cancer rates. Those countries are South Korea, the United States, Italy, France, and Australia, where 60%-90% of thyroid cancer diagnoses are attributable to overdiagnosis. Overall, the incidence of thyroid cancer was less than 1.5 per one million person-years in children younger than 10 years. There were small variations by country and sex.
Thyroid cancer mortalities remain low
Overall, the rate of thyroid cancer mortality among those younger than 20 years in each country was less than 0.1 per 10 million person-years, “corresponding to less than 10 deaths per year in all of the included countries collectively,” note Dr. Vaccarella and colleagues.
“The epidemiological pattern seen in children and adolescents mirrored that seen in adults. These findings suggest that, in affected countries and territories, there might be overdiagnosis in children and adolescents, as has been observed in adults,” they write.
The incidence of thyroid cancer in children and adolescents between 2008 and 2012 ranged from 0.4 per one million person-years in Uganda and Kenya and 13.4 per 1 million person-years in Belarus, where the increase is believed to be related to the Chernobyl nuclear power plant accident and to increased screening in the years following the accident.
Subclinical discoveries may lead to unnecessary measures
Thyroid cancer was once a rare condition. Rates began to increase steadily in the 1990s, corresponding with rapid advances in noninvasive diagnostic imaging. Currently, thyroid cancer is the fifth most diagnosed cancer worldwide in adult women and the third most common in women aged 50 years and younger.
Diagnostic measures ranging from ultrasound and MRI to fine-needle aspiration biopsy have played a large role in the increase in diagnoses. The diagnostic techniques are revealing subclinical cancers in thyroid glands that previously went undetected and that usually do not cause harm over a person’s lifetime. According to Dr. Vaccarella and colleagues, such discoveries can open the door to a wide range of unnecessary measures.
The possible consequences of overdiagnosis include unnecessary treatments, the need to undergo lifelong medical care, and potential adverse effects, which could negatively affect quality of life.
Recent research from the International Agency for Research on Cancer has indicated that there has been an “epidemic of overdiagnosis” of thyroid cancer. The pattern has even reached less affluent regions as diagnostic technologies have become widely available.
“What is surprising is the magnitude of this,” Dr. Vaccarella said in an interview.
“Without overdiagnosis, thyroid cancer would probably still be a relatively rare cancer,” he said.
The study authors have disclosed no relevant financial relationships. Dr. Lamartina has received personal, advisory board, and clinical trial principal investigator fees from Bayer, personal fees from Eisai, and clinical trial principal investigator fees from AstraZeneca. The other editorialists’ financial relationships are listed in the original article.
A version of this article first appeared on Medscape.com.