Abstract:

Background and purpose: The prognosis of differentiated thyroid cancer (DTC) patients with suspicious high thyroglobulin (Tg) concentration and without explicit structural lesions varies from each other, hence the clinical treatment decisions including ¹³¹I therapy remain controversial. This study aimed to explore the effects of ¹³¹I treatment and the therapeutic dose on the clinical outcome of these patients. Methods: The study included 138 DTC patients treated in Department of Nuclear Medicine, Peking Union Medical College Hospital from 2007 to 2021, who had undergone total thyroidectomy and subsequent ¹³¹I therapy. All patients were divided into 3 groups as low dose (dose=1.11 GBq), medium dose (1.11 GBq<dose≤3.70 GBq) and high dose (3.70 GBq<dose≤7.40 GBq) according to the dose of ¹³¹I therapy. We compared the short-term and end-of period response to therapy among these three groups, and further observed the clinical outcome of patients with biochemical incomplete response (BIR) after initial treatment. The receiver operating characteristic (ROC) curve was employed to evaluate the predictive value of stimulated Tg (sTg) levels in patients with structural incomplete response (SIR) and distant metastasis. Results: For the short-term response, the rate of excellent response (ER) was 6.7%, 13.5% and 7.0% in low, medium and high dose group, respectively. The short-term response showed no statistically significant difference among three groups (H=1.02, P=0.60). The end-of-period response among the three groups under routine follow-up also showed no significant difference (H=2.94, P=0.23). No significant difference was observed in the clinical outcome of patients with BIR after routine follow-up and second ¹³¹I treatment (U=324.5, P=0.15). The diagnostic critical point (DCP) of sTg to predict SIR and distant metastasis was 27.5 and 61.7 ng/mL, respectively. Conclusion: DTC patients with suspicious high Tg concentration has high recurrence risk, taking 27.5 ng/mL as the cut-off of sTg is helpful to identify the patients with high recurrence risk early. ¹³¹I treatment is helpful for these patients to achieve ER as soon as possible. However, high-dose ¹³¹I did not have greater benefits on the prognosis of these patients. Second ¹³¹I treatment showed no further benefit for BIR patients.

Key words: Differentiated thyroid cancer, Thyroglobulin, ¹³¹I therapy, Biochemical incomplete response