Nuclear medicine in diagnosis, staging and follow-up of thyroid cancer.

Diagnostic strategy in thyroid cancer is conditioned by epidemiological, pathophysiological, cost-effective issues changing with age and countries. Nuclear medicine has a role mainly in differentiated carcinomas, i.e. in the large majority of thyroid cancers. In diagnosis of thyroid nodule (99m)Tc-perthecnetate is indicated in patients with low TSH levels, multinodular goiter, solid nodules at US negative at FNA. Radiolabeled somatostatin analogs or Metaiodobenzylguanidine (MIBG) can be used in suspicion of medullary carcinoma. There is no role in staging. WBS with 131I has a role after surgical resection of the thyroid gland and it is no more suggested before ablative therapy, because of the possible stunning effect. In the follow-up thyroglobulin (Tg) test is mandatory both after therapy withdrawal or after rhTSH administration. Some authors already suggest to use this test alone, as 1st step, in patients with differentiated carcinoma at low risk of recurrence, but this approach is not yet generally accepted and it has not yet been validated in tumors at intermediate/high risk. WBS with 131I is ever indicated when autoantibodies can affect reliability of Tg values and in presence of high Tg levels to better define a radiometabolic therapy. In case of negative WBS, PET-FDG can be proposed. In WBS, 123I can be an alternative to 131I, but it is not yet generally accepted mainly because of its higher costs. The clinical use of rhTSH to increase accuracy both of Tg and WBS can be already accepted in patients at high risk following hypothyroidism, with a worst prognosis or a low pituitary response.