Expression of sodium iodide symporter in benign and malignant human thyroid tissues

The extent of human sodium iodide symporter (hNIS) expression in different kinds of human thyroid cancer tissues and cell lines remains controversial. In this study, polyclonal antibodies to hNIS were used to analyze the expression of symporter protein in benign and malignant human thyroid tissues. Formalin-fixed, paraffin wax-embedded tissue sections were used. Staining was performed using primary polyclonal antibody of rabbit anti-human hNIS diluted in PBS (1:500). Results showed that 2 of 3 normal tissue, 3 of 6 nodular hyperplasia, one follicular adenoma, 3 of 11 papillary thyroid carcinoma, 1 of 5 follicular carcinoma and none of 3 metastatic thyroid epithelial tissue specimens stained positively for hNIS. A higher percentage of positive staining for symporter protein was found in benign thyroid tissues including normal thyroid tissue, nodular hyperplasia, and adenoma (60%). In contrast, papillary and follicular thyroid carcinomas demonstrated lower symporter protein expression (20%). In conclusion, although the number of tissue samples examined in this study was small, hNIS staining found a higher ratio of symporter protein expression in normal and benign thyroid tissues compared with malignant tissues. Determination of the reason for discrepancies in the expression of hNIS in in vivo and in vitro studies will require further investigation.