Thyroid cancer rates are on the rise in U.S. pediatric patients, a large epidemiologic study shows, and researchers say the trend can’t be explained away purely as overdiagnosis.
However, the extent of a real increase in clinically significant cancers and what might be causing that increase remains unclear, according to authors of the study and two related editorials appearing in the journal Cancer.
Cases of pediatric differentiated thyroid cancer (DTC) cases increased by 4.43% per year in the study, which was based on data from 39 U.S. cancer registries. Increases were seen in both smaller early-stage and larger late-stage tumors, leading study authors to assert that the trend was “unlikely to be explained solely by increased medical surveillance or improved detection.”
“Environmental and individual factors may also have affected rising trends,” said Meredith S. Shiels, PhD, of the National Cancer Institute and coauthors in a report on the study.
A true increase in pediatric thyroid cancer incidence is a possibility, authors of a related editorial said; however, they also expressed concern that inferences drawn from this U.S. cancer epidemiology data may be “artifactual.”
“We believe that first it is most important to closely examine the reasons for the increase that could be attributable to overdiagnosis, given this appears to be a likely explanation,” said authors of one editorial, including Amy Y. Chen, MD, MPH, of Emory University, Atlanta, and Louise Davies, MD, MS, of the Dartmouth Institute for Health Policy and Clinical Practice in Lebanon, N.H.
Overdiagnosis does occur, but the “real component” of the rise in thyroid cancer incidence cannot be ignored, according to a second editorial by David Goldenberg, MD, of Penn State University, Hershey.
“Although many authors are quick to explain the rise in thyroid cancer as an artifact of the overdiagnosis of clinically insignificant thyroid cancers, multiple groups all over the world have shown that this is not sufficient to explain the rise in thyroid cancer,” Dr. Goldenberg said in his editorial.
New data in pediatric patients
Pediatric DTCs are rare, representing just 2%-4% of pediatric malignancies, and they’re particularly rare in relation to adult cases, comprising about 2.3% of thyroid cancer diagnoses overall, according to Dr. Shiels and coauthors of the current study.
“The rarity of pediatric DTC, the lack of information on histologic features, or both have prevented prior studies from analyzing trends by tumor size or cancer stage at diagnosis,” they said.
To address this knowledge gap, Dr. Shiels and colleagues analyzed a total of 7,296 primary DTCs in children aged 0-19 years in data obtained from the North American Association of Central Cancer Registries. Ninety-one percent of these pediatric patients had papillary thyroid cancer, 83% were female, and 76% were between the ages of 15 to 19 years.
The rate of pediatric DTCs increased from 4.77 per million in 1998 to 8.82 per million in 2013, representing an increase of 4.43% per year, they found.
Both localized and more aggressive tumors increased in incidence over that time period, they also found. The annual increase was 4.06% for local stage at diagnosis, 5.68% for regional, and 8.55% for distant disease.
Similarly, increases were seen in small and large tumors alike. The annual percentage increase was 9.46% for tumors smaller than 1 cm, and 4.69% for tumors greater than 2 cm, according to the report.
Looking at age, investigators found that the increases in incidence were significant only for 10- to 19-year-olds, while significant increases were consistently observed for both sexes and for all races and ethnicities.