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Differentiated thyroid cancer is usually a curable disease, for which treatment modalities such as surgery, radioiodine, and thyroid hormone have been used for the last 50 years, yet little consensus has been established due to the lack of prospective randomized controlled therapeutic trials. After an initial surgery, the patients´ outcome can be predicted by staging classification on the basis of several parameters such as the age of the patient, tumor size, tumor grade or differentiation, presence of local invasion, and regional or distant metastases. However, regardless of the pathologic stage, most patients(except those with micopapillary or minimally invasive follicular carcinomas who underwent only a lobectomies) are supposed to receive radioiodine therapy for ablation of any remnant thyroid tissue, which increases the sensitivity of serum Tg and 131I whole body scan used to detect recurrence or metastasis during a long－term follow－up. Until recently, a high dose of 131I has been preferred, however, low dose therapy(30mCi) is a new trend nowadays, which decreases the incidence of both acute and late complications of radioiodine with the same ablation rate. All patients take thyroid hormone after surgery and radioremnant ablation to suppress the level of serum TSH, which is thought to stimulate tumor cell growth.The T4 dose should be adjusted according to the age of the patient, other medical conditions and the risk of recurrence. During the follow－up, the serum Tg level with anti－Tg antibody and the TSH level and 131I whole body scan should be checked regularly. Recently the serum Tg level stimulated by T4 withdrawal or rhTSH injection is suggested to be the most sensitive marker for the detection of recurrence or metastasis. When the stimulated Tg is undetectable (<2ng/mL), residual or metastatic cancer can be nearly excluded; when it is higher than 10ng/mL, a high dose 131I therapy and posttherapy 131I whole body scan are needed. In cases where the localization fails(Tg－positive/131I scan－negative cases), other imaging studies such as high－resolution ultrasonography of the neck, spiral CT of chest, bone X－ray or 99mTc－ MDP bone scan and 18F－FDG PET scan can be useful. 18F－FDG PET is especially sensitive to detect poorly differentiated thyroid cancers that have lost the ability to uptake radioiodine.
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