Diagnosis of papillary thyroid carcinoma is facilitated by using an RT-PCRapproach on laser-microdissected archival material to detect RET oncogene activation

Objective: The purpose of this study was to investigate the value of the ex pression of the RET oncogene (rearranged during transfection) in papillary thyroid carcinomas (PTC) and its variants in the differential diagnosis of thyroid neoplasias. According to the literature RET oncogene activation by chromosomal rearrangements has been exclusively implicated in PTCs. Methods : To establish the incidence of RET activation in PTCs we used 5- to 10-mum sections from archival paraffin blocks. Either parts of the tissue slices were manually dissected or a few distinct cells were microdissected by lase r-mediated manipulation with the Robot-MicroBeam system. RNA was extracted from paraffin-embedded thyroid tumors and the corresponding normal tissue. RT and nested PCR were performed using primers for RET/PTC1, PTC2 and PTC3, or for RET exons 12 and 13. PCR products were resolved by gel electrophore sis. Results: We detected RET transcription in approximately 85% of the PTC s including follicular variants and in isolated cells of the same tissues, but not in nonmalignant thyroid tissue. Conclusions: Our method may serve a s an additional diagnostic tool to characterize ambiguous neoplasias and to identify especially nonpapillary, i.e, follicular tumors, as papillary car cinomas. Additionally, this study has demonstrated that expressed genes can be analyzed from routine histopathological tissue slides or pooled single cells. Large retrospective studies can also be performed with this method. Copyright (C) 2001 S. Karger AG, Basel.