Limited Clinical Value of Periablative Changes of Serum Markers in the Prediction of Biochemical Remission in Patients with Papillary Thyroid Cancer

Remnant thyroid ablation and 1-year stimulated thyroglobulin (sTg) measurement are recommended for those who have undergone total thyroidectomy for differentiated thyroid cancer. The serum Tg kinetics in such patients are still unclear. This study was designed to evaluate whether the periablative change in serum markers can predict biochemical remission in papillary thyroid cancer (PTC) patients. We reviewed the medical records of 185 patients who were given high-dose radioactive iodine ablation therapy from January 2006 to December 2008. Serum Tg, TSH, and anti-Tg antibody (TgAb) were measured on the day and the following 10th day of radioactive iodine administration. We defined preablative sTg as Tg-1, postablative Tg measured on the 10th day of ablation as Tg-2, and the 1-year sTg as Tg-3. ΔTg means Tg2-Tg1. The same definition was applied to TgAb. A biochemical remission defined as Tg-3 < 2 ng/ml was achieved in 144 patients. Among the patients who achieved biochemical remission, PTC recurred in six during a median follow-up of 54 months. Tg-1<3.3 ng/ml (p<0.0001) predicted biochemical remission. Neither the ΔTg nor ΔTgAb was useful for predicting biochemical remission. On the evaluation of recurrence after biochemical remission, Tg-1 > 5.32 (p<0.0001) and Tg-3 > 2.9 (p=0.01) were proven to be statistically significant cutoff values for predicting recurrence. The ΔTg and ΔTgAb were not able to predict recurrence. For the prediction of biochemical remission or recurrence after biochemical remission, preablative sTg was demonstrated to be a statistically significant serum marker. However, short-term changes in biochemical markers including Tg and TgAb around the day of ablation could not provide useful clinical information about biochemical remission or disease recurrence. In conclusion, 1-year sTg measurement cannot be omitted with short-term change