SOMATIC MUTATIONS IN THE RET PROTOONCOGENE IN SPORADIC MEDULLARY-THYROID CARCINOMA

OBJECTIVE We have determined the frequency of specific mutations in th e RET proto-oncogene in sporadic medullary thyroid carcinomas (MTCs) a nd correlated the presence or absence of a codon 918 mutation with the clinical characteristics of these tumours. DESIGN Thirty paraffin-emb edded sporadic MTCs and two frozen MTCs were collected for analysis of specific mutations in the RET proto-oncogene in codons 609, 611, 618 and 620 (exon 10); 630 and 634 (exon 11); 768 (exon 13); 883 (exon 15) and 918 (exon 16). A novel primer was designed which introduced a res triction site for Rsal in the presence of the specific codon 918 mutat ion (ATG --> ACG) in these tumour samples. A 'clinical-genetic' correl ation was performed comparing the presence or absence of the codon 918 mutation with the following clinical characteristics: age at diagnosi s, tumour size, presence or absence of metastases, MTC related morbidi ty, and base line calcitonin levels at diagnosis or most recent follow -up. PATIENTS Patients were classified as having sporadic MTC if there was no family history of C-cell hyperplasia, MTC, phaeochromocytoma o r parathyroid disease. Retrospective review of patient records enabled complete clinical data to be obtained in 28 of 32 patients. MEASUREME NTS Base line calcitonin levels were measured by radioimmunoassay or c alcitonin enzyme linked immunoassay. Cysteine codons in exons 10 and 1 1, specifically codons 609, 611, 618, 620, 630 and 634, were screened for the presence of mutations by sequence analysis. Specific mutations occurring at codons 768, 883 and 918 were screened for by restriction endonuclease digestion of PCR products. RESULTS The mutation at codon 918ATG --> ACG was found in 21 of 32 (66%) MTCs and the mutation at c odon 883GCT-->TTT was found in one of 32 MTCs. Where possible, the pre sence of 'germline-type' mutations in codons 609, 611, 618, 620, 630 a nd 634 were excluded. Ten MTCs did not have a mutation in codons 768, 883 or 918 of the RET proto-oncogene. The presence or absence of the s omatic mutation at codon 918 did not correlate with any of the above c linical characteristics. CONCLUSION Somatic mutations in the RET proto oncogene occur frequently in sporadic MTCs.