ABSTRACT
BACKGROUND: The iodide transport into thyroid cells is an essential step in the biosynthesis of thyroid hormones. The sodium iodide symporter (NIS) which is responsible for iodide transport was cloned recently and identified as a plasma membrane glycoprotein. Recent report suggested the absence of human NIS (hNIS) mRNA expression of papillary carcinoma in thyroid indicates absence of response on radioiodine therapy for distant metastasis. To understand the change of hNIS expression at the stage of metastasis in papillary thyroid carcinomas, we evaluated the expression levels of hNIS mRNA in primary and lymph node metastatic papillary carcinoma tissues. METHODS: Seven pairs of primary and lymph node metastatic tissues were included in this study. The level of hNIS mRNA in lymph node metastatic tissues and primary tissues were evaluated by reverse transcriptase-polymerase chain reaction (RT-PCR). The level of GAPDH mRNA was used as internal control. RESULTS: Two among 6 lymph node metastatic tissues did not show hNIS mRNA even with significant hNIS expressions in papillary carcinoma tissues in thyroid. The levels of hNIS expression of remaining 4 lymph node metastatic tissues were lower than those of corresponding primary tissues. Interestingly, one case showed no hNIS expression in primary tissue, but significant hNIS expression in lymph node metastatic tissue. There was no correlation in hNIS mRNA expression between primary and lymph node metastatic tissues. CONCLUSION: No correlation was found in hNIS mRNA expression between primary and lymph node metastatic tissues, suggesting the measurements of hNIS mRNA level in primary tissues may not predict therapeutic response to radioactive iodine.