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The RET proto-oncogene encodes a protein structurally related to transmembrane receptors with an intracellular tyrosine kinase domain. In human thyroid gland, the RET proto-oncogene is normally expressed in parafollicular C-cells. Thyroid C-cell hyperplasia is associated with inherited medullary thyroid carcinomas and is considered as a pre-neoplastic stage of C-cells disease. It has also been observed in thyroid tissues adjacent to follicular and papillary carcinomas. In order to study the relationship between a misfunctioning of the RET proto-oncogene and the presence of C-cell hyperplasia, we compared a series of thyroid glands presenting sporadic or radiation-associated tumours, as well as samples of unrelated normal thyroid tissues, for alteration in exons 10 and 11 of the gene and for the presence or absence of C-cell hyperplasia. Here we report a significantly higher frequency of C-cell hyperplasia present in peritumoural thyroid tissues of radiation-induced epithelial thyroid tumours, than in peritumoural of sporadic thyroid tumours or in control normal thyroid tissues (P=0.001). A G691S RET polymorphism was present with a higher frequency in radiation-induced epithelial thyroid tumours (55%) than in sporadic tumours (20%) and in control normal thyroid tissues (15%). Interestingly, this polymorphism was associated in the majority (88%) of radiation-induced tumours with a C-cell hyperplasia in the peritumoural tissues. Several explanations for this association are discussed., (Copyright 2002 Cancer Research UK)

Thirty-seven thyroid autonomously hyperfunctioning adenomas were screened for mutations in the TSH receptor (TSHR), G alpha s (gsp), and ras genes. Polymerase chain reaction-amplified fragments of the TSHR C-terminal part (exon 10), the G alpha s (exons 8 and 9), and the three ras genes were obtained from the genomic DNA extracted from 37 tumors and their adjacent normal tissues and were studied by direct nucleotide sequencing and hybridization with synthetic probes. A point mutation in the third intracellular loop (codon 623) of the TSHR was found in 3 of 37 adenomas studied. This mutation codes for a change (Ala to Ser) in the TSHR structure and is somatic and heterozygotic. Constitutive activation of the TSHR was demonstrated by an increase in basal cAMP levels after transfection of Chinese hamster ovary cells with a mutated Ser623-TSHR complementary DNA. Nine gsp[00ae]MDRV[00af]- and one ras-activating mutations were also detected. No simultaneous alteration of the studied genes was present. Thus, in hyperfunctioning thyroid adenomas, our data suggest that a mutational activation of the TSHR and gsp genes may play a tumorigenic role through constitutive activation of the cAMP pathway.