Abstract
In individuals who carry germline mutations in tumor suppressor genes predisposing them to inherited cancer syndromes, occurrence of somatic mutations in the same genes contributes to tumorigenesis. Germline mutations in the RET proto-oncogene predispose individuals to multiple endocrine neoplasia (MEN) type 2 syndromes. Since these mutations are oncogenic by themselves, somatic mutations in the same gene had been thought unnecessary. Recently, a somatic mutation at codon 918 of RET was reported in medullary thyroid carcinoma (MTC) and C-cell hyperplasia in patients with MEN 2A or familial MTC (FMTC), suggesting its possible contribution to tumorigenesis. We describe here a novel somatic mutation at codon 919 in a patient with FMTC carrying a germline mutation at codon 768 that may also be related to tumor progression.