Assessment of ret/PTC-I 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 intr acellular 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 i mplications are currently unclear. This study was undertaken to assess the frequency of RET/PTC-1 expression, any distinctive features of positive tum ours to which it might be related, and its prognostic importance. Archival material from 88 thyroid neoplasms [50 PTCs, eight anaplastic carcinomas (A TCs), 25 follicular thyroid carcinomas (FTCs) and five follicular adenomas (FAs)] were analysed for ret/PTC-1 and H4 expression using 5' nuclease assa y (TaqMan RT-PCR). RNA from the TPC-I 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 o f 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 her e suggests that ret/PTC-1-positive PTCs might also have a similar poor prog nosis 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 n ot been described previously and which may have considerable bearing on tum our morphology. A statistically significant proportion (58%) of ret/PTC-1-p ositive, H4-negative PTCs was associated with chronic inflammatory cell inf iltration of the tumour and/or the surrounding thyroid. This association ha s not been reported previously. Copyright (C) 2000 John Wiley & Sons, Ltd.