Nucl Med Mol Imaging.  2021 Jun;55(3):116-122. 10.1007/s13139-021-00699-2.

Change of Therapeutic Response Classification According to Recombinant Human Thyrotropin‑Stimulated Thyroglobulin Measured at Different Time Points in Papillary Thyroid Carcinoma

• Moon J
• Jeon S
• Park K
• Yoo S
• Kang S
• Cho S
• Kim J
• Lee C
• Song H
• Min J
• Bom H
• Kwon S

• KMID: 2516689
• DOI: http://doi.org/10.1007/s13139-021-00699-2

Abstract

Purpose
We investigated whether response classification after total thyroidectomy and radioactive iodine (RAI) therapy could be affected by serum levels of recombinant human thyrotropin (rhTSH)-stimulated thyroglobulin (Tg) measured at different time points in a follow-up of patients with papillary thyroid carcinoma (PTC).
Methods
A total of 147 PTC patients underwent serum Tg measurement for response assessment 6 to 24 months after the first RAI therapy. Serum Tg levels were measured at 24 h (D1Tg) and 48–72 h (D2-3Tg) after the 2^nd injection of rhTSH. Responses were classified into three categories based on serum Tg corresponding to the excellent response (ER-Tg), indeterminate response (IR-Tg), and biochemical incomplete response (BIR-Tg). The distribution pattern of response classification based on serum Tg at different time points (D1Tg vs. D2-3Tg) was compared.
Results
Serum D2-3Tg level was higher than D1Tg level (0.339 ng/mL vs. 0.239 ng/mL, P < 0.001). The distribution of response categories was not significantly different between D1Tg-based and D2-3Tg-based classification. However, 8 of 103 (7.8%) patients and 3 of 40 (7.5%) patients initially categorized as ER-Tg and IR-Tg based on D1Tg, respectively, were reclassified to IR-Tg and BIR-Tg based on D2-3Tg, respectively. The optimal cutoff values of D1Tg for the change of response categories were 0.557 ng/mL (from ER-Tg to IR-Tg) and 6.845 ng/mL (from IR-Tg to BIR-Tg).
Conclusion
D1Tg measurement was sufficient to assess the therapeutic response in most patients with low level of D1Tg. Nevertheless, D2-3Tg measurement was still necessary in the patients with D1Tg higher than a certain level as response classification based on D2-3Tg could change.

Keyword

Recombinant human thyrotropin; Thyroglobulin; Papillary thyroid carcinoma ; Response classification; Radioactive iodine