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ObjectiveMutations in theRETgene are responsible for hereditary medullary thyroid cancer (MTC) and may vary between ethnic groups. We report the spectrum of mutations detected in patients with MTC in a referral center in Greece.Patients and methodsScreening forRETmutations was performed in 313 subjects from 188 unrelated families: 51 patients had clinical suspicion for familial disease, 133 were apparently sporadic, four patients had only C cell hyperplasia, and 125 were family members. Exons 8, 10, 11, and 13–16 were screened.ResultsA total of 58 individuals (30.85%) wereRETmutations carriers, 120 (63.8%) were finally classified as sporadic, 13 apparently sporadic cases (9.8%) were identified withRETmutation: ten carried the exon 8 at codon 533 mutation (previously reported), two the exon 14 at codon 804 mutation, and one the exon 13 at codon 768 mutation. Six patients (3.19%) with clinical features of multiple endocrine neoplasia type 2A and negative forRETmutations were classified as ‘unknown cause’. The mutations of hereditary cases were as follows: 21 cases (36.2%) in exon 8 codon 533, 19 (32.8%) in exon 11 codon 634, nine (15.5%) in exon 10, five (8.6%) in exon 16, three (5.2%) in exon 14 codon 804, and one in exon 13 codon 768 (1.7%).ConclusionThe spectrum ofRETmutations in Greece differs from that in other populations and the prevalence of familial cases is higher. The exon 8 (Gly533Cys) mutation was the most prevalent in familial cases unlike other series, followed by exon 11 (codon 634) mutations which are the most frequent elsewhere. The wide application of genetic screening in MTC reveals new molecular defects and helps to characterize the spectrum of mutations in each ethnic group.