To analyze the relationship between serologically biochemical response and the disease progression trend and prognosis evaluated by traditional structural imaging in patients with radioactive iodine-refractory differentiated thyroid cancer (RAIR-DTC) treated by apatinib.

A retrospective study was performed on apatinib-treated (phase Ⅱ) patients (n=19; 9 males, 10 females; age 46.0 (41.0, 57.5) years) with locally advanced/metastatic RAIR-DTC in Peking Union Medical College Hospital from March 2016 to June 2022. The relationships between serum thyroglobulin (Tg) and response evaluation criteria in solid tumors (RECIST) 1.1 structural imaging efficacy evaluation and disease progression trend were analyzed. The relationships between change of Tg after dose adjustment and the change of maximum diameter of target lesions in structure imaging were also discussed. Mann-Whitney U test and Wilcoxon signed-rank test were used to analyze the data.

During the median 49.41 months follow-up, the baseline Tg was 363.20(13.08, 2 490.50) μg/L. The Tg time-to-response was 0.47(0.47, 0.98) months, which was 1.80 (1.30, 1.90) months for RECIST 1.1. After 2, 4 and 8 weeks of initial treatment, the median Tg of the whole cohort decreased by 38.68%, 64.70% and 78.94%, respectively. After 8 weeks, the reducing degree of maximum diameter of target lesions was 33.48%. According to the best response, patients were divided into two groups: partial response (PR) group (n=15) and stable disease (SD) group (n=4). The median decreasing degree of Tg in PR group and that in SD group were 87.00% and 28.79%, and the reducing degree of maximum diameter of target lesions in corresponding groups were 45.00% and 21.22%. According to the final efficacy evaluation, patients were further divided into two groups: progressive disease (PD) group (n=13) and non-PD (including PR and SD) group (n=5). The median increasing degree of Tg in PD group was higher than that in non-PD group (381.55% vs 175.43%; U=10.00, P=0.037). The increasing degree of Tg and that of the maximum diameter of target lesions were 167.31% and 2.14% after the 1st adjustment, which were 231.06% and 9.73% after the 2nd adjustment. The differences of changes in Tg and maximum diameter of target lesions before and after the 1st dose adjustment were statistically significant (z values: -3.06 and -2.23, P values: 0.002 and 0.026).

During the apatinib treatment of RAIR-DTC, Tg can reflect the therapeutic effect of apatinib earlier than traditional imaging (RECIST 1.1), indicating the disease progression trend more sensitively.

Thyroid neoplasms; Molecular targeted therapy; Drug therapy; Thyroglobulin; Response evaluation criteria in solid tumors; Prognosis