Rudolf-Virchow-Preis 1995. The role of RET proto-oncogene mutation analysis in the diagnosis of multiple endocrine neoplasia type 2 (MEN 2) gene carriers and in the discrimination of sporadic and familial medullary thyroid carcinomas and pheochromocytomas.

The RET proto-oncogene codes for a receptor-type tyrosine-kinase with to date unknown ligand. Recently, germline point-mutations in RET cysteine codons of the extracellular cysteine-rich domain (encoded by exons 10 and 11) and in the tyrosine-kinase domain (encoded by exon 16) at codon 918, have been associated with the syndromes of multiple endocrine neoplasia (MEN) type 2A, MEN type 2B and familial medullary thyroid carcinoma (FMTC). In our recent studies we have analyzed tumor and germline DNA extracted from formalin-fixed and paraffin-embedded specimens of 45 patients and additional blood samples of 38 possible MEN 2 gene carriers for the presence of RET point mutations in exons 10 and 11 by non-radioactive single strand conformation polymorphism analysis (PCR-SSCP) and for exon 16 by heteroduplex gel electrophoresis. Mutational analysis was performed by fluorescence-based dideoxy terminator cycle sequencing of PCR-products with an automated DNA sequencer. Materials included 19 patients with MEN 2A associated tumors (13 medullary thyroid carcinomas, 6 pheochromocytomas), 3 patients with MEN 2B associated medullary thyroid carcinomas and 23 patients with clinically sporadic tumors (16 medullary thyroid carcinomas, 7 phenochromocytomas). In all 19 MEN 2A patients we found RET germline point-mutations either at cysteine codons 634 (14), 630 (1) in exon 11 or at codon 618 (4) in exon 10. All 3 MEN 2B patients demonstrated germline point mutations at codon 918 (Met-->Thr) in exon 16. In 2 patients with clinically sporadic medullary thyroid carcinomas we found a point mutation at codon 634 both in DNA of the tumor and normal tissue, indicating the presence of a de novo germline mutation. In 5 sporadic medullary thyroid carcinomas and 2 pheochromocytomas we found a somatic point mutations were identified in 11 patients. Our results indicate that mutational analysis of the RET proto-oncogene is not only suitable to identify and subtype MEN 2 gene carriers using blood DNA but also to distinguish sporadic from inherited medullary thyroid carcinomas and phenochromocytomas analyzing DNA extracted from archival tissue specimens.