Sodium iodide symporter expression and radioiodine distribution in extrathyroidal tissues

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Abstract
The functional role of the sodium iodide symporter (NIS) in extrathyroidal tissues was investigated by examining its mRNA and protein expression, together with the evidence of radioiodine (131I) uptake in 302 patients who underwent 131I total body scanning, following the administration of high doses of 131I for a papillary or follicular thyroid carcinoma. By using a real-time kinetic quantitative RT-PCR and immunohistochemistry, the expression of NIS protein was detected mainly in secretory tissues. In parallel, 131I uptake was evidenced in the majority of patients in the salivary glands (in 39%) and stomach (in 78%), but was found in breast in only 4 young female patients. These data demonstrate a strong correlation between the organ radioactivity distribution, as observed in vivo, and NIS protein expression. Interestingly, 131I is rarely concentrated by mammary glands, even when large doses are administered. Moreover, a 131I transfer in secretion fluids may represent a potential source of contamination responsible for false positive images and diagnostic pitfalls.