Recurrence detection in differentiated thyroid cancer patients with elevated serum level of antithyroglobulin antibody: special emphasis on using 18F‐FDG PET/CT

Objective A clinical challenge is presented by differentiated thyroid cancer (DTC) patients who show increased serum antithyroglobulin antibody (TgAb) level with undetectable thyroglobulin (Tg) and negative radioiodine whole body scan (I‐WBS). The aim of this study is to investigate the recurrence in DTC patients with elevated TgAb by using ¹⁸F‐FDG PET/CT (PET/CT) in addition to I‐WBS and neck ultrasonography (USG). Subjects and design A total of 276 TgAb+ patients were enrolled. Recurrence was assessed and compared between TgAb+ and TgAb‐ patients. TgAb+ patients were further categorized into two groups of 35–140 U/ml (Group A) and 140 U/ml or greater (Group B), according to receiver operating characteristic (ROC) curve analysis. Tumoural status was evaluated regarding the TgAb positivity and the degree of increase of TgAb. Results Thirty‐seven (13·4%) of 276 TgAb+ patients were finally diagnosed with recurrence, compared with 21 (13·5%) of 156 TgAb‐ patients (P = 0·987). There was a correlation between TgAb level and recurrence (P = 0·032). Recurrence was more common in Group B than Group A (27·8% and 9·9%, respectively, P = 0·001). Recurrence was found in 37·5% of 24 TgAb+/Tg‐ patients who showed a gradually increasing tendency in serial measurements of TgAb. Sixteen cervical foci (21·1%) missed on neck USG and 17 lesions (22·4%) located outside the neck were additionally detected with PET/CT in TgAb+ patients. Conclusions TgAb plays a complementary role to Tg in the detection of recurrence of DTC. Tumour recurrence was more frequent in patients with elevated TgAb level over 140 U/ml or a trend toward increasing levels. PET/CT could provide additional information to I‐WBS and neck USG in detecting tumour recurrence in patients with elevated TgAb.