Genotype-phenotype correlation in hereditary medullary thyroid carcinoma

Background and objective: Hereditary medullary thyroid carcinoma (MTC) is caused by germline mutations of the RET proto-oncogene. A genotype - phenotype correlation has been established, showing clustering of mutations in exons 10 and 11 in classical MEN 2 A syndrome, in exon 16 codon 918 in MEN 2 B syndrome and in exons 13-15 in familial MTC. A line of evidence suggested that the development and the aggressiveness of MTC in the different cancer syndromes is variable. Aim of this study was to compare the phenotype of exon 13-15 mutations with that of exon 11 mutation and possibly draw therapeutical consequences. Patients and methods: We compared the phenotype of 47 patients with mutations in exon 13-15 with 66 patients with exon 11, codon 634 mutation, the classical MEN2A. Patients were further subdivided as index and screening patients. Results: Mean age of 19 index patients with codon 790, 791, 804 or 891 mutation was significant higher compared with 18 index patients with codon 634 mutation (mean age at diagnosis 50+/-12 years; range 30-69 y vs mean age 31+/-9 years; range 17-49 y), tumor stage at operation was favourable (C-cell hyperplasia n=1,; stage I n 8; 11 n=3; III n=2; IV n=2; no operation n=1; no information n=2 vs stage I n=3-, stage II n=6; stage III n=4, no information n=5), cure rate was better (56% vs 38%) and the death rate was lower (n = 2 vs n = 4). In screening patients no differences concerning the age, tumor stage, cure and death rate between patients with exons 13-15 and codon 634 mutations were seen. Conclusions: MTC in patients with exon 790, 791,1 804, 891 mutations displayed a late onset and an indolent course compared to codon 634 mutation, this has to be taken into account when recomending timing and exent of prophylactic surgery.