Antithyroglobulin Antibody Variation During Follow-Up Has a Good Prognostic Value for Preoperative Antithyroglobulin Antibody-Positive Differentiated Thyroid Cancer Patients: A Retrospective Study in Southwest China

OBJECTIVE: Antithyroglobulin antibody (TgAb) is a potential tumour marker for detecting differentiated thyroid cancer (DTC) recurrence, but insufficient data have supported its clinical applications. Our study aimed to describe the changing trend of TgAb after surgery and identify the relationship between this trend and clinical outcomes. PATIENTS AND METHODS: We reviewed the electronic records of 1,686 DTC patients who had undergone total thyroidectomy (TT) and radioactive iodine ((131)I) therapy at West China Hospital of Sichuan University from January 2015 to December 2017. Finally, 289 preoperative TgAb-positive DTC patients were included and divided into four subgroups depending on the clinical outcome: Group A (tumour free), Group B (uncertain), Group C (incomplete biochemical response), and Group D (structural disease). The patient demographics, tumour characteristics, operations, pathology reports, and all serological biomarkers were reviewed and compared, and the prognostic efficacy of TgAb was evaluated. RESULTS: Among all 1,686 patients, 393 (23.65%) were TgAb positive (>40 IU/ml) preoperatively. The TgAb level in Group A decreased significantly after surgery and (131)I therapy and stabilised at a low level after 1–2 years of (131)I therapy. However, in the other three groups, the decrease in TgAb was not significant after treatment. Conversely, TgAb declined slowly and remained stable or increased. The variations in TgAb relative to the preoperative level of Group A were significantly larger than those of Groups B, C, and D at most time points of follow-up (p < 0.001). By receiver operating characteristic (ROC) analyses, the variations of TgAb > −77.9% at 6 months after (131)I therapy (area under the curve (AUC) = 0.862; p < 0.001) and TgAb > −88.6% at 2 years after (131)I therapy (AUC = 0.901; p < 0.001) had good prognostic efficacy in tumour-free survival. When the variation in TgAb > −88.6% at 2 years after (131)I therapy was incorporated as a variable in the American Thyroid Association (ATA) categories, both intermediate- and high-risk patients also had a significantly increased chance of being tumour free (from 75.68% to 93.88% and 42.0% to 82.61%, respectively). CONCLUSIONS: For preoperative TgAb-positive DTC patients, variations in TgAb > −77.9% at 6 months after (131)I therapy and TgAb > −88.6% at 2 years after (131)I therapy had good prognostic efficacy. Their incorporation as variables in the ATA risk stratification system could more accurately predict disease-free survival.