Background: The incidence of thyroid cancer has increased worldwide. We investigated nationwide trends in the incidence and treatment course of pediatric thyroid cancer in South Korea. Methods: Using the National Health Information Database, we analyzed 1580 patients (324 males) <20 years of age diagnosed with thyroid cancer during 2004-2016 in South Korea. The annual percentage change (APC) in the age-standardized incidence rate (ASR) was calculated by joinpoint regression analysis. The initial treatment modality was categorized as either surgery only or surgery with radioactive-iodine treatment (surgery+RAIT), and we defined new treatment events as reoperations or additional RAITs among 1464 patients followed up for ≥12 months. Results: During 2004-2016, the mean ASR per 100,000 person-years increased from 0.6 [confidence interval; CI 0.5-0.8] to 0.9 [CI 0.8-1.1], with a mean APC of 4.0% [CI 1.8-6.2]. The ASRs (APCs) among 0-9-, 10-14-, 15-17-, and 18-19-year olds were 0.07 (9.9% [CI 0.08-20.7]), 0.6 (4.6% [CI 0.2-9.2]), 2.2 (3.9 [CI 1.7-6.0]), and 4.2 (3.5% [CI 0.9-6.2]), respectively. The lobectomy and lymph-node-dissection rates increased (from 18.5% to 33.6%, p = 0.0014; and from 29.6% to 84.5%, p < 0.001; respectively), but the RAIT rate decreased (67.9-39.7%, p < 0.001) during the study period. During a median 6.3-year follow-up, two patients died. New treatment events occurred in 56 (10.7%) of patients in the initial surgery-only group (n = 523). In the initial surgery+RAIT group (n = 941), 316 patients received two or more RAITs within 2 years, and 80 (12.8%) of the remaining 625 patients underwent new treatment events. In the surgery+RAIT subgroup, the event-free survival rate was lower in 0-14-year olds than in 18-19-year olds (hazard ratio 2.5 [CI 1.4-4.4]). Conclusions: The pediatric thyroid cancer incidence increased from 2004 to 2012 in South Korea. The lobectomy and lymph-node-dissection rates increased, but the RAIT rate decreased. The higher risk for new treatment events in patients younger than 15 years requiring initial RAIT may be linked to advanced stage at diagnosis, and it needs to be further evaluated.

Hyo Ri Yun

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