[Diagnosis, treatment and follow-up in the case of differentiated thyroid cancer]

For early diagnosis of thyroid cancer, ultrasonography (US) and US-guided fine-needle aspiration biopsy are the methods of choice. Thyroid scintigraphy using Tc-99m pertechnetate can underline the necessity of surgery in case of hypofunctioning nodules. Treatment of thyroid cancer includes total thyroidectomy and staging lymphadenectomy, in the case of lymph node metastases, radical neck dissection of the ipsilateral side. Four weeks after surgery, if TSH exceeds a value of 50 mU/l, with the exception of papillary thyroid cancer pT1a (TNM 1997), radioiodine remnant ablation using activities between 2960 and 3700 MBq I-131 is performed in all other cases. As growth of benign and malignant thyroid cells depends on TSH stimulation, thyroid hormone therapy using TSH suppressive doses (TSH, <0.03 mU/l) follows radioiodine remnant ablation. Additional fractionated external radiation therapy (50 Gy) may be administered in advanced cases (e.g., pT4 N1M0; TNM 1997). Standard follow-up of differentiated thyroid cancer includes measurement of serum thyroglobulin, US of the neck and I-131 whole-body scintigraphy (I-131 WBS). With about 98% the sensitivity of thyroglobulin is very high under TSH stimulation. In case of elevated thyroglobulin, US is the method of choice to detect local recurrences and lymph node metastases of the neck. At defined intervals of follow-up or in case of increasing thyroglobulin, I-131 WBS will be performed under TSH stimulation. With the availability of recombinant TSH (exogenous TSH stimulation) the need to withdraw thyroid hormone over a period of 3-4 weeks (endogenous TSH stimulation) is no longer necessary to perform I-131 WBS. However, in about 20-40% of cases or in the course of disease after several radioiodine therapies, recurrences or metastases may be or become iodine negative. In this case, cationic complexes such as Tc-99m Sestamibi or Tc-99m Tetrofosmin are available to detect less differentiated metastases. In the course of dedifferentiation of malignant thyroid cells, the ability of iodine uptake decreases and uptake of glucose increases. This elevated glucose metabolism can be imaged using FDG PET. Today the combination of PET (metabolic imaging) and CT (morphologic imaging) using PET/CT fusion imaging is the method of choice to image iodine-negative metastases.