Thyroglobulin levels measured at the time of remnant ablation to predict response to treatment in differentiated thyroid cancer after thyroid hormone withdrawal or recombinant human TSH.

The objective of our study was to evaluate the prognostic value of stimulated thyroglobulin levels at the moment of remnant ablation for predicting an initial excellent or a structural incomplete response to treatment according to the risk of recurrence in patients with differentiated thyroid cancer. Patients were divided into two groups according to the preparation mode for remnant ablation (thyroid hormone withdrawal or recombinant human TSH). We included 219 patients followed-up for at least for 24 months after remnant ablation. The primary endpoint was the best response to initial therapy assessed in the first 9-18 months of follow-up. An excellent response was observed in 45.1 % of patients prepared after recombinant human TSH compared to 44.6 % of patients prepared after thyroid hormone withdrawal (P = NS). The cutoff value of thyroglobulin level after recombinant human TSH for predicting an excellent response was 8 ng/ml (n = 51), with a sensitivity of 73.9 %, and a positive predictive value of 61 %. It was similar for patients with low vs. intermediate to high risk of recurrence. This cutoff value for thyroglobulin level after thyroid hormone withdrawal was 22 ng/ml (n = 168), with a sensitivity of 94.7 % and a positive predictive value of 61.7 %. In the thyroid hormone withdrawal group the thyroglobulin cutoff level was 12 ng/ml for low-risk patients compared to 16 ng/ml for those with intermediate to high risk of recurrence (P = 0.003). The cutoff value of the thyroglobulin level for predicting a structural incomplete response to initial treatment was 20 ng/ml after rhTSH, with a negative predictive value of 91.4 %. This level was higher in thyroid hormone withdrawal group, and it was established at 25 ng/ml, with a negative predictive value of 97.7 %. The stimulated Tg level seems to be different depending on the preparation mode (rhTSH or THW) for RA. It has a high NPV to predict the absence of a structural incomplete response and it is also a good predictor of the initial excellent response and the NED status at the end of follow-up.