The value of FDG-PET in the follow-up of differentiated thyroid cancer: a review of the literature.

Well differentiated (follicular and papillary) thyroid cancer (DTC) is characterized by rare occurrence and a good prognosis. However, up to 20% of patients with DTC develop locoregional recurrences, whereas even 8% of patients with such recurrences will eventually die from disease. In some of these patients it is related to incomplete initial treatment, whereas in others it indicates the presence of an aggressive tumor. In this latter case, dedifferentiation may occur with negative I-131 whole body scintigraphy (WBS) results and unreliable Tg measurements. In patients with thyroid cancer metastases that lost the capability of I-131 uptake, other imaging techniques are required to depict the non-functioning metastases, irrespective of the Tg-levels and irrespective of the site of recurrent disease. In this respect, some reports have discussed the value of ultrasonography of the head and neck region with good results for the detection of locoregional disease. We have assessed the role of FDG-PET in patients with I-131 negative WBS and its relation with Tg values and TSH-stimulation based on data that have appeared in the literature. In this review article, a discussion is given on the results published so far.

Feasibility of a randomized trial on adjuvant radio-iodine therapy in differentiated thyroid cancer.

BACKGROUND: Justification for adjuvant radio-iodine (I-131) therapy in differentiated thyroid cancer (DTC) is purely based on retrospective data. This is true for ablative therapy and even more so for high-dosage adjuvant schedules. Randomized trials on the latter application are considered impossible due to anticipated formidable sample sizes required in a disease with an overall excellent prognosis like DTC. OBJECTIVE: To develop and validate a model that could stratify for risk of recurrence, rather than survival, as is usually done in prognostic indices, and secondly, to use this model to estimate the sample size required for a randomized trial. DESIGN, PATIENTS AND RESULTS: From databases of three large Dutch centres, we identified 342 consecutive patients without known residual DTC after (near-) total thyroidectomy. Using Cox proportional hazards analysis, a model was validated that clearly distinguished risk categories of recurrence using commonly available baseline variables. The model included age, N stage at presentation and T stage in papillary carcinoma. According to this stratification, a subset of patients at substantial risk for relapse (30-40%) was identified. They could be eligible for a trial assessing the impact of high-dose adjuvant I-131 on recurrence rates. Assuming a clinically relevant effect of 30% reduction of relapses, 290 patients would have to be entered in either arm (alpha 0.05, power 80%). CONCLUSION: We conclude that even though a randomized trial on this issue will be difficult to design and conduct, sample size is not the main problem.