The molecular links between thyroid disease and breast cancer remain unidentified, and different explanations have been proposed, such as the promoter role of sodium/iodide symporter, as expressed in both breast and thyroid tissues, or the presence of progesterone and estrogen receptors identified in the cytosol of tumor thyroid tissue, but not in normal tissue [36–42]. This evidence concerns the gene SLC5A5 and breast carcinoma.