Harms of Pediatric Thyroid Cancer Overdiagnosis

In Reply In our study,¹ we reported that the incidence rate of pediatric thyroid cancer increased more rapidly during 2006 to 2013 than during 1973 to 2006. We proposed that this is likely owing to a combination of enhanced detection and a concurrent true increase in pediatric thyroid cancer incidence based on increased incidences of large tumors and regionally advanced disease. We have read the comments of Murakami et al and wish to address their concerns regarding the interpretation of the later finding.

Overdiagnosis refers to the phenomenon whereby the increased ability to detect and diagnose small indolent tumors that would never otherwise be symptomatic or require treatment causes an apparent increase in thyroid cancer incidence. It is very difficult to argue that overdiagnosis explains the increased incidence of large tumors, given that these are not generally features of indolent tumors. Murakami et al referenced an article by Midorikawa et al,² which suggests that many pediatric thyroid tumors do not exhibit significant growth after an initial proliferation period. However, this conclusion was based on 2 ultrasonographic examinations over a mean interval of less than 0.5 years. Although important, this observation period is too short to make definitive conclusions about the natural history of thyroid cancer, which is typically slow growing but potentially devastating, especially in the pediatric population. Further information about the natural history of large tumors in children would be necessary to exclude the possibility of a true increase in pediatric thyroid cancer incidence. Murakami et al also reference an article by Milano³ that reports a similar prognosis in adolescents and young adults treated for regionally extended thyroid cancer. This finding is not evidence to suggest that regionally advanced pediatric thyroid cancer is indolent in nature. Instead, this may be interpreted as an argument for treatment of thyroid tumors in these populations to continue achieving low mortality. Without high-quality evidence to the contrary, we believe that regionally advanced disease warrants treatment. Therefore, although the increased incidence of large tumors and advanced disease reported in our study may be explained in part by overdiagnosis, there is insufficient evidence to rule out the possibility of a true increase in thyroid cancer incidence. We agree that avoidance of overdiagnosis is important; however, underdiagnosis and undertreatment can also potentially lead to increased morbidity.