Incidence and Temporal Patterns of Differentiated Thyroid Carcinoma in Children and Adolescents in Germany: A Pooled Analysis Based on Data from the German Malignant Endocrine Tumor Registry and the German Childhood Cancer Registry.

Introduction: The increasing incidence of differentiated thyroid carcinoma (DTC) in children and adolescents has become a growing concern. This study provides the first extensive assessment of incidence patterns and temporal trends of pediatric DTC in Germany, using the best available data from the German Malignant Endocrine Tumor (MET) Registry and the German Childhood Cancer Registry (GCCR) covering a period of 25 years. Patients and Methods: We conducted a register-based incidence and time series analysis, identifying all children and adolescents diagnosed with DTC at ages 0-17 years between 1997 and 2021 in Germany, as recorded in the German MET Registry and/or the GCCR. Age-specific and age-standardized incidence rates (ASR) over time, average annual percentage changes (AAPC), and cross-tabulations were used to evaluate incidence and temporal patterns. Results: We identified 469 DTC cases, including 85.7% papillary thyroid cancer and 9.4% follicular thyroid cancer. The average ASR for the period 1997-2021 was 1.16 per million, with higher rates in females compared with males (1.64 vs. 0.72 per million, respectively). Incidence rates increased with increasing age. The overall ASR increased from 0.84 per million in 1997-2001 to 1.48 per million in 2017-2021, with an AAPC of 3.46% [confidence interval or CI: 2.12-4.83]. The increase was most pronounced in adolescents aged 15-17 years (AAPC: 6.79% [CI: 4.43-9.19]). The proportion of incidentalomas rose from 5% in 1997-2001 to 26% in 2017-2021, yet we observed no marked shift in tumor size between symptomatic and incidental cases. Conclusions: Our study revealed a significant increase in pediatric DTC incidence in Germany, most pronounced among adolescents. The observation of an increasing incidence mirrors global trends and presents a complex public health challenge. While improved detection likely contributes to this trend, the stable tumor size distribution suggests that other factors are also in play. The rising detection of incidentalomas suggests enhanced diagnostic practices unrelated to symptoms of thyroid neoplasia. These findings highlight the need to carefully evaluate diagnostic and screening practices in pediatric populations.