Expression microarray analysis of papillary thyroid carcinoma and benign thyroid tissue: emphasis on the follicular variant and potential markers of malignancy.

The most common sub-variant of papillary thyroid carcinoma (PTC) is the so-called follicular variant (FVPTC), which is a particularly problematic lesion and can be challenging from a diagnostic viewpoint even in resected lesions. Although fine needle aspiration cytology is very useful in the diagnosis of PTC, its accuracy and utility would be greatly facilitated by the development of specific markers for PTC and its common variants. We used the recently developed Applied Biosystems 1700 microarray system to interrogate a series of 11 benign thyroid lesions and conditions and 14 samples of PTC (six with classic morphology and eight with follicular variant morphology). TaqMan(R) reverse transcriptase-polymerase chain reaction was used to validate the expression portfolios of 50 selected transcripts. Our data corroborates potential biomarkers previously identified in the literature, such as LGALS3, S100A11, LYN, BAX, and cluster of differentiation 44 (CD44). However, we have also identified numerous transcripts never previously implicated in thyroid carcinogenesis, and many of which are not represented on other microarray platforms. Diminished expression of metallothioneins featured strongly among these and suggests a possible role for this family as tumour suppressors in PTC. Fifteen transcripts were significantly associated with FVPTC morphology. Surprisingly, these genes were associated with an extremely narrow repertoire of functions, including the major histocompatibility complex and cathepsin families.

Assessment of ret/PTC-1 rearrangements in neoplastic thyroid tissue using TaqMan RT-PCR.

Among oncogenes studied in thyroid cancers, a specific activated form of c-ret has been found in a minority of papillary thyroid carcinomas (PTCs). In these tumours, c-ret is activated when by somatic rearrangements, the intracellular domain of RET is juxtaposed with the amino-terminal portion of a different donor gene such as H4, thereby generating a chimeric transcript (ret/PTC-1). The functional effects of c-ret activation and its prognostic implications are currently unclear. This study was undertaken to assess the frequency of RET/PTC-1 expression, any distinctive features of positive tumours to which it might be related, and its prognostic importance. Archival material from 88 thyroid neoplasms [50 PTCs, eight anaplastic carcinomas (ATCs), 25 follicular thyroid carcinomas (FTCs) and five follicular adenomas (FAs)] were analysed for ret/PTC-1 and H4 expression using 5' nuclease assay (TaqMan RT-PCR). RNA from the TPC-1 cell line was included as a positive control for c-ret activation. No FTC or FA displayed activation of ret/PTC-1, though all expressed H4. c-ret activation was found in 24% of PTCs (12 of 50), in 87.5% of ATCs (7 of 8), and in 33% of the combined PTC/ATC group. The frequency of c-ret activation in the aggressive ATC variants noted here suggests that ret/PTC-1-positive PTCs might also have a similar poor prognosis and a follow-up study on this cohort is in progress. Ninety per cent of ret/PTC-1-positive tumours failed to express H4, a phenomenon that has not been described previously and which may have considerable bearing on tumour morphology. A statistically significant proportion (58%) of ret/PTC-1-positive, H4-negative PTCs was associated with chronic inflammatory cell infiltration of the tumour and/or the surrounding thyroid. This association has not been reported previously.

ret/PTC-1 Activation in Hashimoto Thyroiditis.

Activation of ret/PTC-1 has been documented in a minority of papillary thyroid carcinomas (PTC). In a recent study, the authors' group detected the presence of ret/PTC-1 in association with a background of florid lymphocytic thyroiditis (LT) in 58% of cases of PTC studied, which prompted them to examine the incidence of RET/PTC-1 expression in 27 examples of various forms of nonlymphomatous lymphoid infiltration of the thyroid by using TaqMan RT-PCR. Overall, 21 cases (78%) were found to express the chimeric transcript of ret/PTC-1. Eighteen cases of Hashimoto thyroiditis were positive (95%), and, of these, three had concomitant PTC while the remainder had no histologic evidence of associated malignancy. Three cases of lymphocytic thyroiditis demonstrated activated ret/PTC-1 (43%), two having associated PTC. These data suggest either that ret/PTC-1 is an indicator of follicular thyroid cell activation or that ret/PTC-1 activation is an early event in malignant transformation. If the latter is the case, it may be that, in a defined subset of the cell population, ret/PTC-1 activation elicits an autoimmune response, which, while possibly curtailing the development of PTC in the majority of cases, results in destruction of the thyroid parenchyma. Int J Surg Pathol 8(3):185-189, 2000

TSH receptor status of thyroid neoplasms--TaqMan RT-PCR analysis of archival material.

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.