Changing Clinical Presentation of Pediatric Differentiated Thyroid Cancer in Poland: A Retrospective Cohort Study Spanning 45 Years.

Background: Differentiated thyroid carcinoma (DTC) in children is uncommon; clinical presentation over recent decades is incompletely characterized. Methods: This retrospective cohort study analyzed demographic and disease characteristics of consecutive juveniles with DTC treated from 1970 to 2015 at Poland's largest pediatric DTC referral center, Maria Sklodowska-Curie National Research Institute of Oncology, Gliwice, who had available records. Sex, age, histopathological characteristics, and DTC stage were documented. We aimed to identify changes in these variables over time and independent risk factors for lymph node or distant metastases. Trends in these variables were assessed using the Cochran-Armitage test and Spearman correlation. Multivariable logistic regression was performed to identify risk factors associated with lymph node or distant metastases. Results: 475 of 479 patients (99.2%) were included in the analysis; roughly half were age ≥15 years, 10%, <10 years. Papillary thyroid carcinoma (PTC) represented 88% of cases and follicular thyroid carcinoma (FTC) 11%. Tumors ≤2 cm constituted 56% of cases with relevant data; those >4 cm accounted for 12%. Multifocality was observed in 37% and extrathyroidal invasion in 22%. Lymph node metastases were noted in 59% and distant metastases in 16%. Over the observation period, significant trends among new cases included: increased proportion of adolescents >15 years; increased frequency of tumors ≤2 cm, decreased multifocality rates, and increased proportion of PTC versus FTC. Extrathyroidal invasion rates remained appreciable throughout, ranging from 17 to 28% during the 5-year study subperiods after 1990. Lymph node metastases significantly increased in frequency in the central neck, remaining consistently common in lateral sites; presence of distant metastases significantly decreased. In multivariable analysis, multifocality, extrathyroidal invasion, and tumor size were independently associated with lateral lymph node metastases and multifocality, larger tumor size, and N1b metastases with distant spread. Conclusions: Our observations of a rising proportion of diagnoses in adolescence, reductions in primary tumor size, and decreased frequency of multifocality and distant metastases may reflect increased detection of patients with less aggressive DTC at earlier disease stages. Nonetheless, we found persistently substantial rates of locoregionally advanced disease features (multifocality, extrathyroidal invasion, and lymph node metastases), which multivariable analyses suggested have significant associations with lateral lymph node and/or distant metastases.