Predictive Value of Serum Thyroglobulin for Structural Recurrence Following Lobectomy for Papillary Thyroid Carcinoma

Background: The value of serum thyroglobulin/antithyroglobulin (Tg/antithyroglobulin antibody [ATg]) for papillary thyroid carcinoma (PTC) surveillance after lobectomy was investigated. We aimed to examine the association between postlobectomy serum Tg/ATg and PTC structural recurrence and define applicable values for stratification. Methods: PTC patients who underwent lobectomy with adequate serum Tg/ATg data during 2000-2014 were selected. Predictive classifiers of recurrence using random forest were established combining different variables related to serum Tg (ATg-negative patients) or ATg (ATg-positive patients). Cutoff values were determined with receiver operating characteristic curves when applicable. Kaplan-Meier curve and Cox regression were performed to examine the predictive value of elevated Tg/ATg. Results: Of 1451 patients enrolled, 66 (6.3%) and 26 (6.5%) patients in the ATg-negative group (n = 1050) and ATg-positive group (n = 401) developed recurrence. The established classifier of serum Tg (n = 1050) showed a favorable association with recurrence (AUC = 0.81), while serum ATg did not (AUC = 0.72). The optimal cutoff values of the first Tg (FTg, measured 6-12 months after lobectomy) and last Tg (LTg, measured most recently) were 5.3 and 11.0 ng/mL, respectively. Elevated LTg patients had significantly higher recurrence rates than normal LTg patients (23.5% vs. 4.4%, p < 0.05). Patients with elevated FTg had significantly lower recurrence-free survival rates than patients with normal FTg in all ATg-negative patients, low-risk patients, and intermediate- to high-risk patients (according to the American Thyroid Association initial risk stratification) (n = 1050, 583, and 467, all p < 0.05). Multivariate analysis indicated patients with elevated FTg had twice the recurrent risk compared with those with normal FTg (hazard ratio = 2.052). Conclusions: Postlobectomy serum Tg has favorable value for predicting recurrence in PTC patients, and reasonable thresholds could identify patients at higher risk for recurrence during follow-up.