Trends in pediatric thyroid cancer incidence in the United States, 1998‐2013

Background Pediatric differentiated thyroid cancer (DTC) rates have increased over time in the United States and worldwide. Improvements in imaging for the diagnosis of DTC have been hypothesized as a potential driver of these increases. This study stratifies temporal trends in pediatric DTC by stage and tumor size to assess whether rates of large, late‐stage cancers, which are likely to be clinically meaningful, are increasing over time. Methods Age‐standardized incidence rates (ASRs) of DTC and annual percent changes (APCs) in primary DTC rates were estimated for 0‐ to 19‐year‐olds with data from 39 US cancer registries during 1998‐2013. Results During 1998‐2013, 7296 cases of DTC were diagnosed (6652 papillary cases and 644 follicular cases). APCs of pediatric DTCs significantly increased by 4.43%/y [95% CI, 3.74%/y‐5.13%/y], primarily because of increases in papillary histologies. Increasing trends were observed for children aged 10 to 19 years for both sexes and for non‐Hispanic whites, non‐Hispanic blacks, and Hispanics. Rates increased significantly over the time period for all tumor stages (APClocalized, +4.06%/y [95% CI, 2.84%/y‐5.29%/y]; APCregional, +5.68%/y [95% CI, 4.64%/y‐6.73%/y]; APCdistant, +8.55%/y [95% CI, 5.03%/y‐12.19%/y]) and across tumor sizes (APC2 cm, +4.69%/y [95% CI, 2.75%/y‐6.67%/y]). Conclusions Significantly increasing rates of DTC over time among 10‐ to 19‐year‐olds in the United States are unlikely to be entirely explained by increases in medical surveillance during childhood because rates of large and late‐stage DTC are increasing over time. Future studies should examine environmental and other factors that may be contributing to rising DTC rates. Significantly increasing rates of pediatric differentiated thyroid cancer between 1998 and 2013 have been reported in the United States. They are unlikely to be entirely explained by increases in medical surveillance during childhood because rates of large and late‐stage differentiated thyroid cancer are increasing over time.