Prognostic Factors and Competing Risk Analysis in Early-Stage Follicular Thyroid Carcinoma: A Population-Based Study

Background Follicular thyroid carcinoma (FTC) behaves differently from papillary thyroid carcinoma. Although early-stage FTC generally has favorable outcomes, risk within AJCC stage I-II is not uniform, and robust evidence focusing exclusively on this group is limited. Methods We identified 4220 patients with AJCC stage I-II FTC in the SEER database (2010-2022). The primary endpoint was disease-specific survival (DSS). We estimated cumulative incidence functions (CIFs) for thyroid cancer–specific and other-cause mortality and evaluated prognostic factors using Fine-Gray competing-risk regression. Multivariable modeling and nomogram construction were not pursued because only one variable met significance in univariable analyses. Results Across follow-up, other-cause mortality exceeded thyroid cancer–specific mortality; at ∼10 years, other-cause death was ∼6% while thyroid cancer–specific death remained <1.5%. In competing-risk regression, AJCC stage II was the sole significant predictor of thyroid cancer–specific mortality vs stage I (SHR 7.76; 95% CI 2.09-28.8; P = 0.002). Other demographic, tumor, and treatment variables were not significant or were non-estimable due to sparsity. Conclusions Early-stage FTC shows low cancer-specific mortality overall, but risk is concentrated in stage II, underscoring clinically meaningful heterogeneity within “early stage.” These findings support stage-attuned counseling and follow-up and highlight the importance of competing-risk methods when interpreting outcomes in FTC.