Appropriateness of 14-year cutoff in pediatric differentiated thyroid cancer: Comparison of clinical characteristics and long-term outcomes in 14 years and younger and 15-18 years age groups.

[BACKGROUND] Pediatric differentiated thyroid cancers (DTCs) differ in pathophysiology, presentation, and clinical outcomes from adult DTCs. However, the cutoff age for defining pediatric DTCs remains debatable, with the American Thyroid Association (ATA) and International Incidence of Childhood Cancer (IICC) report recommending different cutoffs of 18 and 14 years, respectively. In this study, we investigated the appropriateness of 14-year cutoff by comparing the clinical characteristics and long-term outcomes in the 14 years and younger and 15-18 years age groups.

[METHODS] Data of DTC patients, aged 18 years and older, from 1981 to 2016, were sequentially extracted and compared between two age groups: ≤14 and 15-18 years.

[RESULTS] Total of 176 pediatric DTC patients were included (age group ≤14 years: n = 75; age group 15-18 years: n = 101). None of the baseline clinical characteristics were significantly different between the two age groups. At 2-year follow-up, patients in the age group ≤14 years had significantly higher incomplete response rate compared to those in the age group 15-18 years (69% vs. 42%, respectively, p < .001). However, over a median follow-up of 10.6 years (interquartile range: 7.7-15.5), the 5- and 10-year Disease-free survival (DFS) probabilities were not significantly different (p = .406). On multivariate analysis, incomplete response at 2-year follow-up was the sole independent predictor of poor DFS (hazard ratio: 5.85, 95% confidence interval: 1.69-20.23).

[CONCLUSIONS] Subdivision of pediatric DTCs into less than or equal to 14 years and 15-18 years age groups did not have any long-term predictive value. The cutoff of 18 years as recommended by ATA is reasonable and should be uniformly followed to avoid inconsistencies and confusion.