Endocrine Abstracts

NIS and Tg are viewed as characteristic markers for thyrocytes. They are still expressed in a high percentage of differentiated and undifferentiated thyroid carcinomas but these data are obtained by conventional immunohistochemistry. Here we used tissue microarrays and confocal microscopy to compare subcellular localization of Tg and NIS in a large series of benign and malignant thyroid samples.

Methods

157 papillary (PTC), 56 follicular (FTC), 112 anaplastic (UTC), 109 oxyphilic thyroid carcinomas (OX) were compared to 89 normal thyroids (NT), 83 benign adenomas (BA) and 44 thyroid specimens obtained from Graves’ disease (GT). Using standard techniques of confocal microscopy and specific anti-Tg and anti-NIS antibodies we analyzed all tissues for total and for membrane specific staining.

Results

In good agreement with previous reports we found the highest Tg expression (all in cytoplasm) in normal tissue but app. 1/3 of the tissue was negative. Similarly, NIS staining (in the membrane) was positive only in ¾ of all normal tissue but practically in all Graves patients. In contrast, in only 30% BA stained positive for NIS (membrane) or Tg. Thyroid carcinomas showed a comparable to normal Tg expression in the differentiated tumours but even though NIS was positive to a high percentage staining restricted to the membrane was found in only 8% of UTC and OX and in only 15–20% of PTC and FTC with very high individual variability.

Discussion

These data are clearly at variance to the much higher percentage of positive NIS staining in previous reports. Using confocal microscopy correct membranous NIS staining appears to be low under unstimulated conditions in most benign and malignant tumours. The particularily low rates in OX and UTC may explain the low therapeutic success rate using radioiodine in these tumours (supported by Deutsche Krebshilfe).