In cases of papillary and follicular thyroid cancer, radioactive Iodine-131 (131I) is used to ablate residual normal (and malignant) thyroid tissue after thyroidectomy, with high rates of efficacy.1 Targeted delivery of the NIS gene as a mode of cancer gene therapy represents an opportunity to bring the proven therapeutic potential of I131 to bear against other cancer types. This evidence concerns the gene SLC5A5 and cancer.