Practical initial risk stratification based on lymph node metastases in pediatric and adolescent differentiated thyroid cancer

Background: Data on the risk stratification of pediatric differentiated thyroid cancer (DTC) remain scarce. This study aimed to evaluate the predictors of structural persistent/recurrent disease and revise an initial risk-stratification system in pediatric DTC patients. Methods: This retrospective cohort study included 203 patients (aged <20 years) from two tertiary referral centers in Korea. The extent of cervical lymph node (LN) metastasis was classified based on the location or number of metastatic LNs. Results: During a median follow-up duration of 5.5 years, structural persistent/recurrent disease was observed in 51 (25%) patients, including 22 (11%) with distant metastases. The presence of extrathyroidal extension (ETE) and lateral cervical LN metastases or more than five metastatic LNs were independent predictors for structural persistent/recurrent disease. The presence of bilateral lateral cervical LN metastases or >10 metastatic LNs were independent predictors for distant metastasis. A total of 67 (33%), 72 (35%), and 64 (32%) patients were classified into the low-, intermediate-, and high-risk groups, respectively, based on the presence of ETE and the extent of cervical LN metastases. Compared to the low-risk group, the intermediate- and high-risk groups had a significantly greater risk of structural persistent/recurrent disease (hazard ratio = 7.32, p = 0.008, and hazard ratio = 24.28, p < 0.001, respectively). Conclusions: This revised initial risk-stratification system based on the presence of ETE and the extent of cervical LN metastasis is useful for predicting the clinical outcomes of pediatric DTC patients. The findings could facilitate the practical use of a risk-stratification system.