Long-term oncological outcomes of follicular thyroid cancer in adolescents and young adults: A nationwide population-based study

Background: Follicular thyroid carcinoma (FTC) in adolescents and young adults (AYAs) is rare and data on long-term oncological outcomes are scarce. This study aimed to describe the long-term recurrence and survival rates of AYAs with FTC, and identify risk factors for recurrence. Methods: This is a retrospective cohort study combining two national databases, including all patients aged 15–39 years, diagnosed with FTC in The Netherlands between 2000 and 2016. Age, sex, tumor size, focality, positive margins, angioinvasion, pT-stage, and pN-stage were included in a Cox proportional hazard model to identify risk factors for recurrence. Results: We included 192 patients. Median age was 31.0 years (IQR 24.7–36.3) and the male to female ratio was 1:4.1. Most patients presented with a minimally invasive FTC (MI-FTC) (95%). Five patients presented with synchronous metastases (2.6%), including two with locoregional metastases (1%) and three with distant metastases (1.6%). During a median follow-up of 12.0 years, three patients developed a recurrence (1.6%), of which one patient developed a local recurrence (33%), and two patients a distant recurrence (67%). Five patients died during follow-up (2.6%). Cause of death was not captured. A Cox proportional hazard model could not be performed due to the low number of recurrences. Conclusions: FTC in AYAs is generally characterized as a low-risk tumor, as it exhibits a very low recurrence rate, a high overall survival, and it typically presents as MI-FTC without synchronous metastases. These findings underscore the favorable long-term oncological prognosis of FTC in AYAs.