Relation of Stimulated Post Ablation Tg to Tumor Recurrence

Thyroid cancer recurrence in patients clinically free of disease with undetectable or very low serum thyroglobulin values.

Kloos RT

J Clin Endocrinol Metab. 2010 Dec;95(12):5241-8. Epub

One hundred seven patients had initial thyroid cancer surgery and subsequent remnant radioiodine ablation. Patients underwent recombinant human TSH (rhTSH)-mediated diagnostic whole-body scan and rhTSH-stimulated thyroglobulin (Tg) measurement before April 2001 if they had no antithyroglobulin antibodies, were clinically free of disease, and had one or more undetectable ( ¤0.5 ng/ml) or low (0.6-1 ng/ml) basal Tg measurements on levothyroxine. Patients were stratified according to their rhTSH-Tg responses: group 1, Tg 0.5 ng/ml or less (68 patients); group 2, Tg from 0.6 to 2.0 ng/ml (19 patients); and group 3, Tg greater than 2 ng/ml (20 patients).

In group 1(tg =or<.5), two of 62 patients (3%) with follow-up recurred. In group 2 (TG .6-2), 63% converted to group 1, whereas two of 19 (11%) converted to group 3 and then recurred. Sixteen of the initial 20 group 3 (TG >2) patients (80%) recurred, including recurrence rates of 69 and 100% for those with an initial rhTSH-Tg greater than 2.0 ng/ml but 5.0 ng/ml or less, and 4.6 ng/ml or greater, respectively. One group 3 patient died of distant metastases. rhTSH-Tg more accurately predicted tumor recurrence than basal Tg. An rhTSH-Tg threshold of 2.5 ng/ml or greater optimally predicted future recurrence with sensitivity, specificity, and negative and positive predictive values of 80, 97, 95, and 84%, respectively.

The prevalence of postablation thyroid cancer recurrence is predicted by the rhTSH-Tg response with an optimal Tg threshold of 2.5 ng/ml. Still, recurrent disease occurs in some patients with an initial rhTSH-Tg of 0.5 ng/ml or less.

Comment

This study affirms the predictive value of low post-ablation TG, but also reminds us that such predictions are not fool-proof, and for conservative physicians , encourages continued follow-up vigilance.