Changes of thyroglobulin antibody after 131I ablation in patients with papillary thyroid carcinoma and its relationship with efficacy

Objective To investigate the changes in thyroglobulin antibody (TgAb) after 131I ablation and its relationship with 131I ablation efficacy in papillary thyroid carcinoma (PTC) patients. Methods A total of 223 PTC patients (67 males, 156 females, average age: (38.9±11.7) years) with no distant metastasis from June 2012 to June 2016 were included and classified into G1 group(≥40 kU/L, n=48) and G2 group(<40 kU/L, n=175) according to TgAb level 6 months after 131I ablation (TgAb2). G1 group was further divided into 2 subgroups according to the changes of TgAb: S1 group (n=25) with TgAb decreased more than or equal to 50%TgAb at the baseline (TgAb1), S2 group (n=23) with TgAb decreased less than 50%TgAb1 or increased TgAb. The efficacy in terms of 131I ablation success rate (IBR) between G1 and G2 was compared. The difference of IBR between S1 and S2 was also analyzed. χ2 test and Mann-Whitney u test were used to analyze the data. Results There were 39.5%(88/223) patients with high TgAb (≥40 kU/L) before 131I ablation, and the rate decreased to 21.5%(48/223) 6 months after 131I ablation (χ2=16.926, P<0.05). IBR of G1 group was lower than that of G2 group (52.1%(25/48) vs 83.4%(146/175), χ2=20.698, P<0.05), but the radioiodine dose of group 1 was higher (1 110(1 110, 3 700) vs 1 110(1 110, 1 110) MBq; u=3 616.000, P=0.035). S2 group showed lower IBR (34.8%(8/23) vs 68.0%(17/25); χ2=5.296, P=0.021) than S1 group. After being followed up for 24 months (median), the persistence or recurrence rates in S1 and S2 groups were 16.0%(4/25) and 43.5%(10/23; χ2=4.378, P=0.036). Conclusions The change of TgAb is associated with 131I ablation efficacy. Dynamically monitoring the changes could provide evidence for predicting clinical outcome of PTC patients. Key words: Thyroid neoplasms; Radiotherapy; Iodine radioisotopes; Thyroglobulin; Antibodies