It has been demonstrated that thyroid cancers with low iodine avidity tend to have higher glucose metabolism, which is related to reduced NIS and increased glucose transporter 1 gene expression, so 18FDG-PET/CT seems to have the highest sensitivity in this setting and may be helpful in identifying patients at higher risk or patients unlikely to benefit from additional 131I therapy. This evidence concerns the gene SLC5A5 and thyroid cancer.