Undetectable pre-ablation thyroglobulin levels in patients with differentiated thyroid cancer: it is not always what it seems

Value of stimulated pre-ablation thyroglobulin as a prognostic marker in patients with differentiated thyroid carcinoma treated with radioiodine

OBJECTIVE

To determine which Thyroglobulin (Tg) level after levothyroxine (LT₄) withdrawal (stimulated thyroglobulin - sTg) measured before radioiodine therapy (RAIT) is able to predict incomplete response to treatment of differentiated thyroid carcinoma (DTC) with greater sensitivity and specificity one year after initial treatment with I¹³¹.

METHODS

A chart review was performed in which 375 patients with DTC treated with RAIT were included. The sTg was measured in all patients prior to treatment with I¹³¹. Follow up were then performed one year later. Initial sTg levels were associated to DTC outcomes. A receiver operating characteristic (ROC) curve was performed to achieve a sTg level able to predict which patients would have a greater chance of having an incomplete response to RAIT.

RESULTS

Incomplete response to treatment was found in 122 patients (32.5%), this group had a mean sTg of 23.2 ng/mL. ROC curve showed that the optimal cut-off sTg level was 4.4 ng/mL. (sensitivity: 72.1%; specificity: 72.3%; accuracy: 72.2%; positive predictive value of 55.7%; and negative predictive value: 84.3%).

CONCLUSION

sTg pre-ablation is a valuable predictor of DTC incomplete response to treatment one year after RAIT. Levels of 4.4 ng/ml or more showed higher accuracy to predict this outcome.

Recombinant human thyroid-stimulating hormone-aided remnant ablation achieves a response to treatment comparable to that with thyroid hormone withdrawal in patients with clinically relevant lymph node metastases

It has already been shown that remnant ablation in patients with thyroid cancer and lymph node (LN) metastases has similar results when patients are prepared after recombinant human thyroid-stimulating hormone (rhTSH) therapy or thyroid hormone withdrawal (THW). Due to the current changes in the risk-of-recurrence classifications, we decided to evaluate the initial response to treatment and the outcome at medium-term follow-up in 40 consecutive patients with clinically relevant lymph nodes who received radioiodine remnant ablation after rhTSH therapy (n = 20) or THW (n = 20). Each patient received either 100 or 150 mCi 131-I for ablation based on TNM status, and the mean amounts of 131-I used in the 2 groups were not significantly different. An excellent response to treatment was observed in 45% of the patients prepared after rhTSH therapy compared to 20% of those prepared after THW (p = 0.08). Three patients (2 in the THW group and 1 in the rhTSH group) who had N1a in the initial surgery presented with structural persistence as an initial response to treatment. One patient in the THW group had a follow-up of the persistent disease with no surgical treatment, and 2 others received a lateral LN dissection. When the status at final follow-up was considered (median follow-up 3.3 years, range 3-4.2), 60% of the patients ablated after rhTSH therapy were considered with no evidence of disease, compared to 30% of those who underwent THW. The frequency of structural persistence (metastatic LN) was similar in the 2 groups (15 vs. 25%), and the distribution of the responses at final follow-up was not statistically significantly different (p = 0.12). We conclude that preparation after rhTSH therapy seems to be as effective as after THW for patients with clinically relevant LN metastases.