Study of TgAb levels dynamics and ¹³¹I therapeutic efficacy prediction value in postoperative papillary thyroid cancer patients

Objective To investigate the change trend of thyroglobulin antibody (TgAb) level after radioiodine therapy and its predictive value for the initial ¹³¹I remnant ablation efficacy in postoperative papillary thyroid carcinoma (PTC) patients with pre-ablation TgAb (pa-TgAb) positivity.

Methods Nine hundred and eighty PTC patients who received ¹³¹I therapy at Tianjin Medical University General Hospital from September 2019 to July 2022 were retrospective analyzed. Ultimately, 172 pa-TgAb positive (pa-TgAb level≥40 IU/ml) patients with Tg<0.2 ng/ml were enrolled (33 males, 139 females; age (44.2±12.1) years). Clinical data, serological results, and imaging findings were collected. Based on the TgAb levels six months after the ¹³¹I remnant ablation, the patients were divided into G1 group (TgAb level<40 IU/ml) and G2 group (TgAb level≥40 IU/ml). Successful ablation rates were compared between two groups. Based on the time it takes for pa-TgAb to turn negative after successful treatment with the last ¹³¹I remnant ablation, the patients were divided into ≤6 month group, 7–12 month group, >12 month group, and persistent positive group. Patients were categorized into response and non-response groups based on therapeutic efficacy evaluation at 6 months following the last ¹³¹I therapy for unresectable local or distant metastatic lesions (referred to as metastasis ablation) delta thyroglobulin antibodies (ΔTgAb) were compared between two groups. For continuous data, intergroup comparisons were performed using the t-test or Mann-Whitney U test. For categorical data, intergroup comparisons were performed using the χ² test. Multivariate Logistic regression analysis was employed to investigate the influencing factors of TgAb conversion to negative after ¹³¹I remnant ablation. Receiver operating characteristic (ROC) curves were used to evaluate the predictive value of factors related to ¹³¹I remnant ablation and ¹³¹I metastasis ablation for TgAb conversion to negative.

Results The follow-up duration ranged from 24 to 46 months, with a median follow-up time of 16.5 months. The proportion of patients with positive pa-TgAb was 17.6%(172/980). Of the 142 patients who underwent ¹³¹I remnant ablation, 10 were lost to follow-up (a loss rate of 7.0%). Six months after the ¹³¹I remnant ablation of 132 patients, the success rate reached 66.7%(88/132). A significant difference was observed between G1 group (75.0%, 57/76) and G2 group (55.4%, 31/56) (χ²=7.724, P<0.01). Among the 122 patients with successful ablation after the last ¹³¹I remnant ablation, 112 achieved pa-TgAb seroconversion during the follow-up period, with values reaching 72.1%(88/122) within 6 months, 11.5% (14/122) at 7–12 months, and 8.2% (10/122) after 12 months, achieved satisfactory therapeutic effect. The results of the multivariate Logistic regression analysis showed that, pa-TgAb level, Hashimoto′s thyroiditis, N stage, and the interval between surgery and the initial ¹³¹I remnant ablation were influencing factors for TgAb turning negative within 6 months after ¹³¹I remnant ablation (HR=0.998, 4.054, 0.414, 0.989; all P<0.05). Thirty patients with metastatic lesions underwent ¹³¹I therapy, two patients were lost to follow-up (a loss rate of 6.7%); among them, 20 patients were in the response group and 8 patients were in the nonresponse group. The difference in ΔTgAb between the response group (0.76(0.64, 0.89)%) and the nonresponse group (−0.03(−0.59, 0.21)%) was statistically significant (Z=−3.718, P<0.001). The results of the ROC curves analysis indicated that after successful initial ¹³¹I remnant ablation, pa-TgAb positive PTC patients with pa-TgAb levels<226 IU/ml and interval between surgery and the initial ¹³¹I remnant ablation<62 days had a higher likelihood of TgAb conversion to negative within 6 months; patients undergoing ¹³¹I therapy with pa-TgAb levels<473 IU/ml and ΔTgAb>62.0% indicated good therapeutic efficacy.

Conclusion The level of pa-TgAb, the interval between surgery were closely related to the efficacy of initial ¹³¹I remnant ablation, and ΔTgAb can provide a reference for predicting the therapeutic efficacy of ¹³¹I metastasis ablation in patients.