Differentiated thyroid cancer. New concept of radioiodine ablation

Ablative radioiodine therapy is the treatment of choice in patients with differentiated thyroid cancer, the only exception being the unifocal, very small papillary thyroid cancer. The TSH-stimulation can be achieved by a waiting period for 2-3 weeks after thyroidectomy without medication or by the use of recombinant human TSH (rhTSH). Both options lead to high success rates. 'Single dose cure' using activities between 1.85 and 3.7 GBq 131I is standard. Since 2010 rhTSH is approved by the EMA for the indications pT1-4, N0-1, cM0. Survey studies did not find any inferiority of ablation with rhTSH or iatrogenic hypothyroidism in the high-risk patient group. Renal clearance is not reduced after rhTSH administration, thus the 131I blood dose and the whole body doses are lower in patients under rhTSH. Comparing identical 131I activities after endogeneous or exogeneous stimulation, rhTSH will minimize the acute adverse effects of 131I. A short-term withdrawal of levothyroxine some days before rhTSH-injection lowers the iodine plasma level, which may be advantageous for the ablation success if lower 131I activities are used. A rhTSH-based diagnostic 131I whole-body scintigraphy 3-6 months after ablation is standard for therapy control. At this time, the rhTSH-stimulated thyroglobulin-level is essential for a personalized risk stratification. Tg-measurements by a second generation assay should be used for follow-up care. Metaanalyses have shown that radioiodine ablation lowers the mortality rate, the risk of locoregional recurrences and the risk of late metastasizing. Therefore, ablation has shown a clear benefit. (orig.)