Quantitative measurements of iodine avidity in surgical specimens (primary tumour and lymph node metastases) of 28 patients were compared to immunohistochemical expression of the thyroid-stimulating hormone receptor, thyroid peroxidase (TPO), pendrin, sodium–iodide symporter (NIS) and mutational status of BRAF and the TERT promoter. The gene discussed is SLC26A4; the disease is metastatic malignant neoplasm in the lymph nodes.