Regulation of thyroid follicular cell proliferation and function is mediated by the interaction of TSH with its receptor (TSHr) on the plasma membrane. While it is recognized clinically that responsiveness of thyroid epithelial tumours to TSH varies with the histological type and grade of neoplasm, the level of TSHr expression in these different tumours has not been quantified hitherto. The aim of this study was to provide this information. Total RNA was extracted from 125 samples of formalin-fixed, paraffin-embedded thyroid tissue comprising 48 papillary (PTC), 29 follicular (FTC), eight anaplastic (ATC), and five medullary thyroid carcinomas (MTC), in addition to 35 samples of either follicular adenoma (FA) or normal thyroid tissue. Samples were reverse-transcribed and analysed using TaqMan polymerase chain reaction (PCR). TSHr expression was shown to be similar to normal in FA and inversely related to the grade of the majority of thyroid cancers other than MTC, in which, as expected, there was negligible expression. It is concluded that reduced expression of TSHr implies decreased responsiveness to TSH manipulation and is therefore a clinically important prognostic indicator in thyroid cancers.
Copyright 1999 John Wiley & Sons, Ltd.