SAT-339 Predictors and Prognostic Significance of Post-operative Anti-thyroglobulin Antibody Positivity in Patients With Differentiated Thyroid Cancer: A Retrospective Cohort Study

Abstract Disclosure: M. Leeder: None. A. Krishnan: None. A. Day: None. S.F. Awad: None. J.M. Lakoff: None. Background: Serum thyroglobulin (Tg) is a key prognostic marker in differentiated thyroid cancer (DTC). Twenty-five percent of DTC patients have positive serum anti-thyroglobulin antibodies (TgAb), which directly interfere with Tg measurement, thus impacting prognostication. Growing evidence suggests that TgAb-positivity is associated with an increased risk of persistent/recurrent disease (PRD). Little is known about what risk factors are associated with TgAb-positivity in DTC patients. Methods: We retrospectively studied 329 DTC patients aged ≥18 who underwent total thyroidectomy and had at least one documented TgAb on follow-up seen at Kingston Health Sciences Centre between January 1, 2000, and September 1, 2023. Using a proportional hazards model, we examined the association between nine potential risk factors and TgAb-positivity. Using the Cox model for time-dependent covariates, we examined the association between “current” TgAb status and risk of PRD. We investigated TgAb status alone and in combination with Tg status. Results: Of 329 DTC patients aged ≥ 18 who underwent total thyroidectomy with documented TgAb on follow-up, 38.9% had at least one positive TgAb. Lymphocytic thyroiditis (LT) was the strongest predictor of TgAb-positivity (HR=2.28, 95% CI 1.55-3.33, p<0.0001). Other associated risk factors were stage > 1 (p=0.009), family history of thyroid cancer (HR = 2.27, 95% CI, 1.02-5.05, p=0.044), and age at diagnosis (HR = 0.98, 95% CI 0.97-1.00, p = 0.028). TgAb-positivity was associated with increased PRD risk (HR=2.8, 95% CI, 1.5-5.3, p=0.0015). Combined positive TgAb and detectable Tg were associated with increased PRD risk compared to combined TgAb-negativity and undetectable Tg (HR = 29.6, 95% CI, 6.3-138.1). LT was associated with decreased PRD risk (HR = 0.39, 95% CI, 0.17 to 0.92, p=0.031). Conclusions: Longer follow-up periods and high-sensitivity assays may account for an increased prevalence of TgAb-positivity among DTC patients. LT was the most significant predictor of TgAb-positivity. Higher cancer stage, family history of thyroid cancer, and younger age at diagnosis were also associated with TgAb-positivity. TgAb-positivity is associated with increased PRD risk. This risk may be higher in patients with combined positive TgAb and detectable Tg. While LT is associated with TgAb-positivity, these patients have a lower risk of PRD. Presentation: Saturday, July 12, 2025