RET PTC AND RET TYROSINE KINASE EXPRESSION IN ADULT PAPILLARY THYROIDCARCINOMAS/

The prevalence of RET/PTC rearrangements in papillary thyroid carcinom as (PTCs) varies widely in different studies, and an association of RE T/PTC presence with tumor behavior remains to be clarified. A prospect ive study of 50 adult PTCs examined, using RT-PCR, the prevalence of t he 3 main RET rearrangements and also of RET tyrosine kinase (TK) doma in sequence expression. The genetic findings were correlated with the MACIS clinical prognostic score and with individual clinical parameter s. Three of the patients had been exposed to radiation in childhood or adolescence. Four of the PTCs contained RET/PTC1, confirmed by sequen cing, and none contained RET/PTC2 or RET/PTC3. The prevalence of RET r earrangements overall was 8%, but in the subgroup of 3 radiation-expos ed patients it was 66.6%. Interestingly, RET tyrosine kinase domain me ssenger ribonucleic acid was detectable in 70% of PTCs using RET exon 12/13 primers and was detectable in 24% of PTCs using RET exon 15/17 p rimers. RT-FCR for calcitonin and RET extracellular domain, however, w as negative. There was no association between the presence or absence of RET/PTC in the patient's tumor and clinical parameters. We conclude that RET/PTC1 is the predominant rearrangement in PTCs from adults wi th a history of external irradiation in childhood. RET TK messenger ri bonucleic acid expression is common in PTCs, using RT-PCR, and cannot be used to infer the presence of specific RET rearrangements or of RET activation.