Fluorodeoxyglucose-positron emission tomography/computed tomography (FDG-PET/CT) is valuable for visually staging recurrent thyroid cancer, particularly in patients with suspected radioactive iodine-refractory pulmonary metastasis from thyroid cancer. In Case 1, despite undergoing radioactive iodine therapy for pulmonary metastasis following papillary thyroid carcinoma surgery, an increase in the metastatic lesion was observed, prompting the suspicion of iodine refractivity. FDG-PET/CT imaging revealed strong abnormal FDG accumulation in the pulmonary metastases. In Case 2, a pulmonary metastasis from thyroid cancer was originally pathologically diagnosed as a poorly differentiated tumor, and FDG-PET/CT imaging was conducted due to suspected iodine refractivity. Both patients showed a single pulmonary metastasis site that was considered iodine-refractory. Radiofrequency ablation (RFA) for pulmonary metastases of thyroid cancer may delay the introduction of tyrosine kinase inhibitors (TKIs), which are commonly used for iodine-refractory thyroid cancer; however, their use is associated with side effects and high medical costs. RFA was performed in cases 1 and 2, and both patients progressed without recurrence; thus, TKIs were not administered. Visual staging using FDG-PET/CT before TKI initiation for pulmonary metastases from thyroid cancer is beneficial in determining treatment strategies.

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