Purpose: This study aimed to identify the predictive value of the low preablation-stimulated thyroglobulin (ps-Tg, <2 ng/ml) for excellent response to radioiodine remnant ablation in differentiated thyroid carcinoma.
Patients and methods: A total of 398 consecutive patients who underwent total thyroidectomy and radioactive iodine remnant ablation therapy were reviewed retrospectively. Each patient was risk-stratified using the American Joint Cancer Committee and risk staging systems and using response to the initial therapy reclassification system. ps-Tg was defined as less than 2 ng/ml with negative thyroglobulin antibody under thyroid-stimulating hormone stimulation. A multivariate analysis was carried out for ps-Tg, TNM stage, and other potential clinical and pathologic factors.
Results: We followed the patients for a median of 32.7 months. Overall, an excellent rate of response was achieved in 367 (92.2%) of the 398 patients. The only variable found to be associated with excellent response was ps-Tg (odds ratio=2.530, P=0.009) by multivariate analysis. The subgroups with 0<ps-Tg<1 ng/ml had a higher success ablation rate than the patients with 1≤ps-Tg<2 ng/ml. Overall, 31 patients were not achieving an excellent response, and most of them showed an indeterminate response. Only two patients who achieved an excellent response were confirmed to have developed recurrence in the follow-up, both in the local regional lymph nodes.
Conclusion: There is a good probability that most low ps-Tg (<2 ng/ml) patients can achieve an excellent response. ps-Tg is the essential and independent predictor for an excellent response in the patients with ps-Tg less than 2 ng/ml, which is better than TNM stage.