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Germline mutations in codon 918 of exon 16 of theRETgene (M918T) are classically associated with multiple endocrine neoplasia type 2B (MEN 2B) with highly aggressive medullary thyroid cancer (MTC), pheochromocytoma and a unique phenotype. The objectives of this study are to describe the rare M918VRETmutation discovered in 8 MTC kindreds from Brazil lacking the MEN 2B phenotype classically observed in M918T patients and to investigate the presence of a founder effect for this germline mutation. Eight apparently sporadic MTC cases were diagnosed with the germline M918VRETmutation. Subsequently, their relatives underwent clinical and genetic assessment (n = 113), and M918V was found in 42 of them. Until today, 20/50 M918V carriers underwent thyroidectomy and all presented MTC/C-cell hyperplasia; the remainder carriers are on clinical follow-up. None of the M918V carriers presented clinical features of MEN 2B. Their clinical presentation was heterogeneous, and the age at tumor diagnosis ranged from 24 to 59 years. Lymph node metastases were present in 12/20 patients, and presumable distant metastases in 2/20; in contrast, we observed a carrier of up to 87 years of age without evidence of MTC. Ethnographic fieldwork and haplotype analyses suggested that the founder mutation first settled in that area fifteen generations ago and originated from Portugal. Our study is the first to demonstrate theRETM918V mutation co-segregating in 8 familial MTC kindreds with validated evidence of a founder effect. We suggest that M918V MTC should be clinically considered an American Thyroid Association (ATA) moderate-risk category.

Multiple endocrine neoplasia type 2 (MEN2) is an autosomal dominant genetic disease caused by RET gene germline mutations that is characterized by medullary thyroid carcinoma (MTC) associated with other endocrine tumors. Several reports have demonstrated that the RET mutation profile may vary according to the geographical area. In this study, we collected clinical and molecular data from 554 patients with surgically confirmed MTC from 176 families with MEN2 in 18 different Brazilian centers to compare the type and prevalence of RET mutations with those from other countries. The most frequent mutations, classified by the number of families affected, occur in codon 634, exon 11 (76 families), followed by codon 918, exon 16 (34 families: 26 with M918T and 8 with M918V) and codon 804, exon 14 (22 families: 15 with V804M and 7 with V804L). When compared with other major published series from Europe, there are several similarities and some differences. While the mutations in codons C618, C620, C630, E768 and S891 present a similar prevalence, some mutations have a lower prevalence in Brazil, and others are found mainly in Brazil (G533C and M918V). These results reflect the singular proportion of European, Amerindian and African ancestries in the Brazilian mosaic genome.

Objectives The presence of thyroglobulin (Tg) in needle washouts of fine needle aspiration biopsy (Tg-FNAB) in neck lymph nodes (LNs) suspected of metastasis has become a cornerstone in the follow-up of patients with papillary thyroid carcinoma (PTC). However, there are limited data regarding the measurement of anti-Tg antibodies in these washouts (TgAb-FNAB), and it is not clear whether these antibodies interfere with the assessment of Tg-FNAB or whether there are other factors that would more consistently justify the finding of low Tg-FNAB in metastatic LNs. Materials and methods We investigated 232 FNAB samples obtained from suspicious neck LNs of 144 PTC patients. These samples were divided according to the patient’s serum TgAb status: sTgAb- (n = 203 samples) and sTgAb+ (n = 29). The TgAb-FNAB levels were measured using two different assays. Tg-FNAB was also measured using two assays when low levels (< 10 ng/mL) were identified in the first assay of the metastatic LNs from the sTgAb+ samples. Results The TgAb-FNAB results were negative in both assays in all samples. Low levels of Tg-FNAB were identified in 11/16 of the metastatic LNs of the sTgAb+ patients and 16/63 of the sTgAb- patients (p < 0.05) using assay 1. The measurement of the Tg-FNAB levels using assay 2 indicated additional metastases in 5 LNs of the sTgAb+ patients. Conclusions Factors other than the presence of TgAb-FNAB may contribute to the higher number of metastatic LNs with undetectable Tg-FNAB in the sTgAb+ group. In addition, the measurement of Tg-FNAB using different assays was useful to enhance the diagnosis of metastatic LNs, particularly when cytological and Tg-FNAB results are discordant.