Increase in the incidence of differentiated thyroid carcinoma in children, adolescents, and young adults (AYA): A population-based study.

Abstract

9523 Background: Studies have shown an increase in thyroid cancer incidence among adults since the 1990s. However, few studies have evaluated this occurrence among children and AYA. Increases resulting from enhanced detection are most likely to involve small tumors. The objective of this study is to investigate trends in incidence of differentiated thyroid carcinomas in children and AYA by size and sex. Methods: This is an ecological time-trend study. Cases of differentiated thyroid cancer (1984-2008) in patients younger than 30 years old were selected from SEER 9 cancer registries using International Classification of Diseases for Oncology 3rd edition (ICD-O-3) codes for papillary and follicular cancers (codes 8050/3, 8052/3, 8130/3, 8260/3, 8290/3, 8330-8332/3, 8335/3, 8340-8344/3, 8450/3 and 8452/3). Patients who had multiple primary tumors were excluded from the study. SEER*Stat software was used to calculate age-standardized rates (estimated per 1,000,000 persons; World Standard Population) and annual percentage changes (APC) were calculated using Joinpoint model. Results: Rates ranged from 2.77 (1990) to 7.45 (2002) for males and from 17.19 (1987) to 41.3 (2008) for females. Overall, a significant increasing trend in incidence was observed for females (APC=3.20, 95%CI 2.80, 3.60). When a stratified analysis based on tumor size was performed, significant increasing trends were noted for the following categories: 0.5-0.9 cm (Males: APC=3.50, 95%CI 1.50, 5.40; Females: APC=7.30, 95%CI 5.90, 8.80), 1.0-1.9 cm (Males: APC=3.20, 95%CI 1.00, 5.40; Females: APC=2.90, 95%CI 2.20, 3.70), and ≥ 2cm (Males: APC=1.30, 95%CI 0.30, 2.40; Females: APC=2.50, 95%CI 1.70, 3.20). However, no statistically significant trends were noted for tumors <0.5 cm (Males: APC=2.50, 95%CI -0.30, 5.40; Females: APC=2.0, 95%CI -6.90, 11.80). Conclusions: Incidence rates for differentiated thyroid carcinoma are also increasing among children and AYA in the United States. The absence of increasing trends for small tumors (< 0.5cm) rules out diagnostic scrutiny as the only explanation for the observed results. Environmental, dietary and genetic factors should be investigated.