RET 634 germline/gonadal mosaicism generating a second pathogenic amino acid change in multiple endocrine neoplasia type 2A.

Genetic testing for germline RET pathogenic variants, which cause the Multiple Endocrine Neoplasia Type 2 (MEN2) syndrome, has become crucial in managing patients with medullary thyroid carcinoma (MTC). Classically, RET heterozygous missense pathogenic variants are transmitted in a Mendelian autosomal dominant pattern, of which germline/gonadal mosaicism has never been reported. We report the novel occurrence of a MEN2A patient's family in which the siblings inherited three different RET 634 genotypes: wild type (p.Cys634), p.Cys634Gly or p.Cys634Arg heterozygous pathogenic variants. We hypothesized that germline/gonadal mosaicism, derived from an inherited + early somatic mutation in the mother or a double de novo mutation during maternal embryogenesis, led to this rare event in the RET gene. Exome analysis of the proband's deceased mother's paraffin-embedded thyroid tissue confirmed the three nucleotides in the same 634 codon position. For the first time, we describe germline/gonadal mosaicism in RET, generating a second pathogenic amino acid change in the same codon causing MEN2A. Our finding shows that RET parental mosaicism, confirmed by somatic exome sequencing, might explain discrepant genotype cases in siblings with inherited cancers.

THE COMBINED USE OF CALCITONIN DOUBLING TIME AND 18F-FDG PET/CT IMPROVES PROGNOSTIC VALUES IN MEDULLARY THYROID CARCINOMA: THE CLINICAL UTILITY OF 18F-FDG PET/CT.

OBJECTIVE: Calcitonin and carcinoembryonic antigen (CEA) doubling times are established prognostic markers in medullary thyroid cancer (MTC). On the other hand, 18F-fluorodeoxyglucose (FDG) positron emission tomography/computed tomography (PET/CT) shows an increased rate of detection with high blood tumor marker levels in several cancers. This study aimed to analyze the ability of 18F-FDG PET/CT to determine prognosis in the follow-up of patients with MTC. METHODS: Medical records of 17 patients with MTC who underwent 18F-FDG PET/CT were analyzed retrospectively. All patients were classified into two groups: stable disease or progressive disease. RESULTS: Eight patients presented with progressive disease, and all of them showed 18F-FDG uptake (100%), compared to only 3 of 9 patients who presented in stable condition (33%). 18F-FDG PET/CT results were able to distinguish progressive from stable disease (P = .009). Calcitonin levels >4,020 pg/mL (P = .0004), CEA levels >26.8 ng/mL (P = .04), and a calcitonin doubling time <24.1 months (P = .015) were associated with progressive disease in our cohort. The proportion of variance explained that predicted progressive disease was 32% for 18F-FDG uptake, 27.1% for a calcitonin doubling time of 24.1 months, and 41.2% for doubling time plus 18F-FDG PET/CT. CONCLUSION: 18F-FDG uptake was able to distinguish progressive from stable disease. However, this tool should not replace the validated calcitonin doubling time, but rather the combination of information could improve the clinical re-assessment and better identify high-risk patients who require more careful surveillance. ABBREVIATIONS: CEA = carcinoembryonic antigen CT = computed tomography 18F-FDG = 18F-fluorodeoxyglucose MTC = medullary thyroid cancer PET = positron emission tomography PVE = proportion of variance explained sCT = serum calcitonin SUV = standard uptake value US = ultrasound.

Integration of a postoperative calcitonin measurement into an anatomical staging system improves initial risk stratification in medullary thyroid cancer.

OBJECTIVE: Staging systems applied to medullary thyroid cancer (MTC) rely on initial clinical and pathological features and do not consider the response to treatment. To determine whether MTC staging can be improved by incorporating the first postoperative calcitonin measurement. PATIENTS AND MEASUREMENTS: Eighty-five patients being monitored for MTC (median follow-up 5 years) were retrospectively classified according to both the American Joint Committee on Cancer (AJCC) and the proposed combined risk stratification system (low, intermediate and high risk), which incorporates the first postoperative calcitonin measurement, using the outcomes no evidence of disease (NED), biochemical evidence of disease, structurally identifiable disease and death. RESULTS: Ninety per cent of AJCC I patients were classified as NED at final follow-up. When we added a postoperative calcitonin measurement, 95% low-risk patients were classified as NED at final follow-up. AJCC stages I and IV were associated, respectively, with no occurrence and a high rate (63%) of structurally identifiable disease. Stages II and III yielded similar predictions of structurally identifiable disease, 13% and 14%, respectively. When we included the postoperative calcitonin level, the patients with structural evidence of disease included none from the low-risk group, 10% from the intermediate group and 63% from the high-risk group. The proportion of variance explained analysis (PVE) was better for the combined risk stratification system (54%) than for the AJCC system alone (32%). CONCLUSION: Including the first postoperative calcitonin measurement with the anatomical staging system can better predict the clinical outcome of patients with MTC and refine the follow-up of these patients.

A ten-year clinical update of a large RET p.Gly533Cys kindred with medullary thyroid carcinoma emphasizes the need for an individualized assessment of affected relatives.

OBJECTIVE: Reviewing the clinical outcomes of a large kindred with a RET p.Gly533Cys mutation, 10 years after the first description of this kindred, has provided an important set of clinical data for healthcare decision-making. DESIGN AND PATIENTS: We identified 728 RET533 Brazilian relatives, spread out over 7 generations. We performed clinical examination, biochemical and imaging analyses in the proband and in 103 carriers. MEASUREMENT AND RESULTS: The proband has been followed without evidence of structural disease in the last 10 years but with elevated calcitonin. The clinical and surgical features of 60 thyroidectomized RET533 relatives were also described. Forty-six patients had MTC (21-72 years), and 11 patients had C-cell hyperplasia (CCH) (5-42 years). Twelve MTC patients with lymph node metastases had a tumour size of 0·7-2·8 cm. Calcitonin level and CEA were correlated with disease stage, and none of the patients presented with an altered PTH or metanephrine. A 63-year-old woman developed pheochromocytoma and breast cancer. Two other RET533 relatives developed lung squamous cell carcinoma and melanoma. CONCLUSIONS: A vast clinical variability in RET533 presentation was observed, ranging from only an elevated calcitonin level (3%) to local metastatic disease (25%). Many individuals were cured (42%) and the majority had controlled chronic disease (56%), reinforcing the need for individualized ongoing risk stratification assessment. The importance of this update relies on the fact that it allows us to delineate the natural history of RET 533 MEN2A 10 years after its first description.

Long-Term Follow-up of Patients With Autonomous Thyroid Nodules Treated With Radioiodine.

PURPOSE: This article aims to describe the presentation of Plummer disease and its evolution after radioiodine treatment and determine factors that may influence treatment efficacy. PATIENTS AND METHODS: The sample included retrospective medical records of 165 adult patients with toxic nodular goiter treated with radioiodine between 1997 and 2017, followed up at a single thyroid center. RESULTS: The efficacy of treatment with a single dose of radioiodine was higher than 90%. The mean radioiodine activity was 28.9 ± 3.4 mCi. The mean time between radioiodine performance and hyperthyroidism resolution was 3.6 ± 3.0 months, ranging from 1-12 months. After the first year, 33.9% of the patients were under hypothyroidism, 59.4% under euthyroidism, and 6.7% under hyperthyroidism. Among the nonresponders, the variables that showed statistical difference were the presence of multinodular goiter and the radioiodine activity (mean, 25.5 ± 6.5 mCi; median, 30 [15-30 mCi]). The cumulative rate of hypothyroidism was 48.9% over 20 years of follow-up. CONCLUSIONS: Radioiodine therapy is an effective and safe treatment. In Plummer disease, high rates of euthyroidism are expected after the radioiodine treatment. Therapeutic failure was observed mainly in patients with larger multinodular goiters treated with lower doses of radioiodine. The evolution to hypothyroidism was mostly observed in younger patients with larger and uninodular goiters.

Germline genetic variants in pheochromocytoma/paraganglioma: single-center experience.

Pheochromocytoma and paragangliomas (PPGLs) are rare neuroendocrine tumors carrying 25-40% pathogenic germline gene variants (PGVs). We evaluated clinical, laboratory, and germline molecular profile of 115 patients with pathologic (14 patients were relatives from 8 different families recruited for genetic survey) confirmed PPGL followed in our institution. Patients with classic MEN2A/MEN2B phenotypes and at-risk relatives underwent direct analysis of RET proto-oncogene, and the remaining had samples submitted to complete next-generation sequencing aiming 23 PPGL-related genes: ATM, ATR, CDKN2A, EGLN1, FH, HRAS, KIF1B, KMT2D, MAX, MDH2, MERTK, MET, NF1, PIK3CA, RET, SDHA, SDHAF2, SDHB, SDHC, SDHD, TMEM127, TP53, and VHL. We also developed a clinical judgment score (CJS) to determine the probability of patients having a potentially hereditary disease. The resulting genetic landscape showed that 67 patients (58.3%) had variants in at least one gene: 34 (50.7%) had exclusively pathogenic or likely pathogenic variants, 13 (19.4%) had pathogenic or likely pathogenic variants and variant of undetermined significance (VUS), and 20 (29.8%) carried only VUS. PGVs were found in RET (n = 18; 38.3%), VHL (n = 10; 21.3%), SDHB and NF1 (n = 8; 17% each), and MAX, SDHD, TMEM127, and TP53 (n = 1; 2.1% each). Direct genetic testing disclosed 91.3% sensitivity, 81.2% specificity, and 76.4% and 93.3% positive predictive value (PPV) and negative predictive values (NPV), respectively. The CJS to identify patients who would not benefit from genetic testing had 75% sensitivity, 96.4% specificity, and 60% and 98.2% PPV and NPV, respectively. In summary, the landscape of PPGL germline gene variants from 115 Brazilian patients resulted in slightly higher prevalent pathogenic and likely pathogenic variants, especially in the RET gene. We suggest a CJS to identify PPGL patients who would not require initial genetic evaluation, improving test specificity and reducing costs.

Risk of malignancy and diagnostic accuracy of fine-needle aspiration biopsy in thyroid nodules with diameters greater than 4 centimeters.

Objective: The risk of malignancy and diagnostic accuracy of fine-needle aspiration biopsy (FNAB) of thyroid nodules (TN) with diameters ≥ 3-4 cm remains controversial. However, some groups have indicated surgical treatment in these patients regardless of the FNAB results. We aimed to evaluate the diagnostic accuracy of the FNAB in systematically resected ≥4 cm TN and if the risk of malignancy is higher in these patients. Subjects and methods: We retrospectively evaluated 138 patients (142 nodules) with TN with diameters ≥4 cm who underwent thyroidectomy. Results: The FNAB results were nondiagnostic/unsatisfactory (ND/UNS) in 2.1% of the cases and benign in 51.4%. They indicated atypia of undetermined significance/follicular lesion of undetermined significance (AUS/FLUS) in 23.9% of cases, follicular neoplasia/suspicious for a follicular neoplasm (FN/SFN) in 9.2%, suspicion of malignancy (SUS) in 8.5%, and malignant in 4.9%. The histopathological analysis after thyroidectomy revealed a thyroid cancer rate of 100% in the FNABs classified as malignant, 33.3% in SUS cases, 7.7% in FN/SFN, 17.6% in AUS/FLUS, and 4.1% in benign FNABs. None of the ND/UNS FNABs were malignant. The global malignancy diagnosis was 14.8% (n = 21). However, the rate of false negatives for FNAB was low (4.1%). Conclusion: We showed that the risk of malignancy in nodules with diameters ≥4 cm was higher compared to the risk of thyroid cancer in TN in general. However, we found a low rate of false-negative cytological results; therefore, our data do not justify the orientation of routine resection for these larger nodules.

Searching for mutations in the HNF1B gene in a Brazilian cohort with renal cysts and hyperglycemia.

OBJECTIVE: To verify the presence of variants in HNF1B in a sample of the Brazilian population selected according to the presence of renal cysts associated with hyperglycemia. SUBJECTS AND METHODS: We evaluated 28 unrelated patients with clinical suspicion of HNF1B mutation because of the concomitant presence of diabetes mellitus (DM) or prediabetes and renal cysts. Genotyping was accomplished using Sanger sequencing or multiplex ligation-dependent probe amplification (MLPA). In positive cases, available relatives were recruited. RESULTS: We found two patients with HNF1B mutations. The first presented the variant p.Pro328Leufs*48(c.983delC) and had DM, renal cysts, and hypomagnesemia. The second presented a heterozygous whole gene deletion in HNF1B, DM, renal cysts, body and tail pancreatic agenesis, and hypomagnesemia; this alteration was also found in his two siblings and his father. CONCLUSION: The recruitment of suspected cases of HNF1B gene mutations in Brazilians due to hyperglycemia and renal cysts presents two positive cases. Our cases contribute to the annotation of clinical and biochemical phenotypes of this rare form of maturity-onset diabetes of the young (MODY).

Genotype and phenotype landscape of MEN2 in 554 medullary thyroid cancer patients: the BrasMEN study.

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.

Risk of malignancy and diagnostic accuracy of fine-needle aspiration biopsy in thyroid nodules with diameters greater than 4 centimeters

ABSTRACT Objective: The risk of malignancy and diagnostic accuracy of fine-needle aspiration biopsy (FNAB) of thyroid nodules (TN) with diameters ≥ 3-4 cm remains controversial. However, some groups have indicated surgical treatment in these patients regardless of the FNAB results. We aimed to evaluate the diagnostic accuracy of the FNAB in systematically resected ≥4 cm TN and if the risk of malignancy is higher in these patients. Subjects and methods: We retrospectively evaluated 138 patients (142 nodules) with TN with diameters ≥4 cm who underwent thyroidectomy. Results: The FNAB results were nondiagnostic/unsatisfactory (ND/UNS) in 2.1% of the cases and benign in 51.4%. They indicated atypia of undetermined significance/follicular lesion of undetermined significance (AUS/FLUS) in 23.9% of cases, follicular neoplasia/suspicious for a follicular neoplasm (FN/SFN) in 9.2%, suspicion of malignancy (SUS) in 8.5%, and malignant in 4.9%. The histopathological analysis after thyroidectomy revealed a thyroid cancer rate of 100% in the FNABs classified as malignant, 33.3% in SUS cases, 7.7% in FN/SFN, 17.6% in AUS/FLUS, and 4.1% in benign FNABs. None of the ND/UNS FNABs were malignant. The global malignancy diagnosis was 14.8% (n = 21). However, the rate of false negatives for FNAB was low (4.1%). Conclusion: We showed that the risk of malignancy in nodules with diameters ≥4 cm was higher compared to the risk of thyroid cancer in TN in general. However, we found a low rate of false-negative cytological results; therefore, our data do not justify the orientation of routine resection for these larger nodules.

A pioneering RET genetic screening study in the State of Ceará, Brazil, evaluating patients with medullary thyroid cancer and at-risk relatives: experience with 247 individuals.

OBJECTIVE: Initial diagnosis of medullary thyroid carcinoma (MTC) is frequently associated with advanced stages and a poor prognosis. Thus, the need for earlier diagnoses and detection in relatives at risk for the disease has led to increased use of RET genetic screening. SUBJECTS AND METHODS: We performed RET screening in 247 subjects who were referred to the Brazilian Research Consortium for Multiple Endocrine Neoplasia (BRASMEN) Center in the State of Ceará. Direct genetic sequencing was used to analyze exons 8, 10, 11, and 13-16 in MTC index cases and specific exons in at risk relatives. Afterward, clinical follow-up was offered to all the patients with MTC and their affected relatives. RESULTS: RET screening was performed in 60 MTC index patients and 187 at-risk family members. At the initial clinical assessment of the index patients, 54 (90%) were diagnosed with apparently sporadic disease and 6 (10%) diagnosed with hereditary disease. After RET screening, we found that 31 (52%) index patients had sporadic disease, and 29 (48%) had hereditary disease. Regarding at-risk relatives, 73/187 were mutation carriers. Mutations in RET codon 804 and the rare p.M918V mutation were the most prevalent. CONCLUSIONS: Performing RET screening in Ceará allowed us to identify a different mutation profile in this region compared with other areas. RET screening also enabled the diagnosis of a significant number of hereditary MTC patients who were initially classified as sporadic disease patients and benefited their relatives, who were unaware of the risks and the consequences of bearing a RET mutation.

Down-regulation of Kir2.6 channel by c-termini mutation D252N and its association with the susceptibility to Thyrotoxic Periodic Paralysis.

Inward rectifying potassium - Kir - channels drive the resting potential to potassium reversal potential and, when disrupted, might be related to muscular diseases. Recently, Thyrotoxic Periodic Paralysis (TPP) has emerged as a channelopathy related to mutations in KCNJ18 gene, which encodes Kir2.6 channel. TPP is a neuromuscular disorder characterized by a triad of muscle weakness, hypokalemia, and thyrotoxicosis, the latter being essential for the crisis. Direct sequencing revealed two heterozygous mutations - D252N and R386C - in two TPP patients. KCNJ18 cDNAs were cloned into mammalian expression plasmids and transiently expressed in HEK 293T cells to investigate the functional effects of Kir2.6 mutations. Patch-clamp and confocal laser scanning microscopy experiments were carried out, comparing the WT channel to its mutants. D252N mutation down-regulates the Kir2.6 activity, decreasing the K+ current density (∼34%) when compared to the WT channel; whereas the mutation R386C shows no significant changes from WT. The mutant D252N Kir2.6 channel also showed a substantial reduction of ∼51% in membrane abundance relative to WT channel. Our study describes the functional consequences of a single amino acid change in Kir2.6 channel. Further analysis regarding hormonal conditions and Kir channel expression are required to provide new clues about the TPP pathophysiology.

Evidence for the founder effect of RET533 as the common Greek and Brazilian ancestor spreading multiple endocrine neoplasia 2A.

OBJECTIVES: About one-quarter of patients with medullary thyroid cancer (MTC) have inherited disease due to mutations in the RET gene. A rare mutation in exon 8 (G533C) of RET, previously described in a large Brazilian family with MEN2A, also appeared to be clustering in Greece, whereas it was rarely reported in other ethnic groups. The aim of this study was to identify a possible common ancestry between these carriers. PATIENTS AND METHODS: Twelve RET G533C mutation carriers, four randomly selected from the Brazilian cohort and eight from apparently unrelated Greek families, were studied for a possible common ancestral origin. RET flanking microsatellite markers at chromosome 10q (D10S197, D10S196, D10S1652 and D10S537) were used. RESULTS: Genomic DNA analysis using these markers showed that many of these apparently unrelated individuals shared a common haplotype indicating a common ancestral origin. CONCLUSION: Our data suggest that Brazilian and Greek patients with MTC carrying the G533C mutation in exon 8 of RET gene originate from a common ancestor. Due to historical reasons, we speculate that the more plausible explanation for the origin of this mutation is in Greece.

Analysis of somatic mutations in BRAF, CDKN2A/p16 and PI3KCA in patients with medullary thyroid carcinoma.

Medullary thyroid carcinoma (MTC), a neuroendocrine tumor originating from thyroid parafollicular cells, has been demonstrated to be associated with mutations in RET, HRAS, KRAS and NRAS. However, the role of other genes involved in the oncogenesis of neural crest tumors remains to be fully investigated in MTC. The current study aimed to investigate the presence of somatic mutations in BRAF, CDKN2A and PI3KCA in MTC, and to investigate the correlation with disease progression. DNA was isolated from paraffin­embedded tumors and blood samples from patients with MTC, and the hotspot somatic mutations were sequenced. A total of 2 novel HRAS mutations, p.Asp33Asn and p.His94Tyr, and polymorphisms within the 3' untranslated region (UTR) of CDKN2A (rs11515 and rs3088440) were identified, however, no mutations were observed in other genes. It was suggested that somatic point mutations in BRAF, CDKN2A and PI3KCA do not participate in the oncogenesis of MTC. Further studies are required in order to clarify the contribution of the polymorphisms identified in the 3'UTR of CDKN2A in MTC.

Macrocalcitonin Is a Novel Pitfall in the Routine of Serum Calcitonin Immunoassay.

CONTEXT: Calcitonin (CT) is a sensitive marker of medullary thyroid carcinoma (MTC) and is used for primary diagnosis and follow-up after thyroidectomy. However, persistently elevated CT is observed even after complete surgical removal without evidence of a recurrent or persistent tumor. OBJECTIVE: To investigate the presence of assay interference in the serum CT of MTC patients who are apparently without a structural disease. PATIENTS AND METHODS: We studied three index MTC cases for CT assay interference and 14 patients with metastatic MTC. The CT level was measured using an immunofluorometric assay. Screening for assay interference was performed by determination of CT levels before and after serum treatment with polyethylene glycol. Additionally, samples were analyzed by chromatography on ultra-performance liquid chromatography and protein A-Sepharose. RESULTS: Patients with biochemical and structural disease showed CT mean recovery of 84.1% after polyethylene glycol treatment, whereas patients suspected of interference showed recovery from 2-7%. The elution profile on UPLC showed that the immunometric CT from these three patients behaved like a high molecular mass aggregate (>300 kDa). Additionally, when these samples were applied to the protein A-Sepharose, CT immunoreactivity was retained on the column and was only released after lowering the pH. CONCLUSIONS: For the first time, our results show the presence of a novel pitfall in the CT immunoassay: "macrocalcitonin." Its etiology, frequency, and meaning remain to be defined, but its recognition is of interest and can help clinicians avoid unnecessary diagnostic investigations and treatment during the follow-up of MTC.

M918V RET mutation causes familial medullary thyroid carcinoma: study of 8 affected kindreds.

Germline mutations in codon 918 of exon 16 of the RET gene (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 M918V RET mutation 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 M918V RET mutation. 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 the RET M918V 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.

Multifocality in Sporadic Medullary Thyroid Carcinoma: An International Multicenter Study.

BACKGROUND: Current surgical standard of care in sporadic medullary thyroid carcinoma (sMTC) consists of a minimum of total thyroidectomy with central neck dissection. Some have suggested thyroid lobectomy with isthmusectomy and central neck dissection for patients with sMTC, given their lower frequency of bilateral disease, although this topic has not been thoroughly studied. This study assessed the prevalence of multifocality in sMTC via a large international multi-institutional retrospective review to quantify this prevalence, including the impact of geography, to assess more accurately the risks associated with alternative surgical approaches. METHODS: A retrospective chart review of sMTC patients from 11 institutions over 29 years (1983-2011) was undertaken. Data regarding focality, extent of disease, RET germline analysis plus family and clinical history for multiple endocrine neoplasia type 2 (MEN2), and demographic data were collected and analyzed. RESULTS: Patients from four continents and seven countries were included in the sample. Data for 313 patients with documented sMTC were collected. Of these, 81.2% were confirmed with negative RET germline testing, while the remaining 18.8% demonstrated a negative family history and no manifestations of MEN2 syndromes other than MTC. Bilateral disease was identified in 17/306 (5.6%) patients, while multifocal disease was noted in 50/312 (16.0%) sMTC patients. When only accounting for germline negative patients, these rates were not significantly different (5.6% and 17%, respectively). Among them, when disease was unifocal in the ipsilateral lobe and isthmus, bilateral disease was present in 6/212 (2.8%) cases. When disease was multifocal in the ipsilateral lobe or isthmus, then bilateral disease was present in 8/37 (21.6%) cases (p < 0.001). No geographic differences in focality were identified. CONCLUSIONS: The 5.6% prevalence of bilateral foci in sMTC suggests that total thyroidectomy should remain the standard of care for initial surgery, as less complete thyroid surgery may fail to address fully the primary site of disease. Whether ipsilateral tumor focality should be an independent factor determining the need for completion thyroidectomy when sMTC is diagnosed after hemithyroidectomy remains to be determined.

Response to initial therapy predicts clinical outcomes in medullary thyroid cancer.

BACKGROUND: Risk stratification in medullary thyroid cancer (MTC) has traditionally relied on standardized anatomic staging systems that, despite providing valuable prognostic information, do not adequately predict the risk of persistent or recurrent disease. As dynamic risk stratification has been demonstrated to be clinically valuable in nonmedullary thyroid cancer, we adapted our response to therapy definitions in order to apply them to MTC. In this study, we evaluate and compare the clinical utility of our previously proposed MTC response to therapy stratification with a traditional standardized anatomic staging system. METHODS: Both the Tumor, Node, Metastasis/American Joint Cancer Committee (TNM/AJCC) staging system and our previously proposed response to initial therapy staging system was evaluated in 287 MTC patients followed for a median of five years. RESULTS: The TNM/AJCC staging system provided adequate risk stratification with regard to disease-specific mortality and the likelihood of having no evidence of disease at final follow-up, but did not adequately stratify patients with regard to the likelihood of having structural persistent disease, biochemical persistent disease, or recurrence. However, the response to initial therapy risk stratification system provided clinically useful risk stratification with regard to disease-specific mortality, the likelihood of having no evidence of disease at final follow-up, the likelihood of having a biochemical persistent disease at final follow-up, and the likelihood of having structural persistent disease at final follow-up. Furthermore, the response to therapy risk stratification system demonstrated a higher proportion of variance explained (54.3%) than the TNM/AJCC system (23.9%). CONCLUSION: Our data demonstrate that a dynamic risk stratification system that uses response to therapy variables to adjust risk estimates over time provides more useful clinical prognostic information than static initial anatomic staging in MTC thyroid cancer.

Comprehensive assessment of the disputed RET Y791F variant shows no association with medullary thyroid carcinoma susceptibility.

Accurate interpretation of germline mutations of the rearranged during transfection (RET) proto-oncogene is vital for the proper recommendation of preventive thyroidectomy in medullary thyroid carcinoma (MTC)-prone carriers. To gain information regarding the most disputed variant of RET, ATA-A Y791F, we sequenced blood DNA samples from a cohort of 2904 cancer-free elderly individuals (1261 via Sanger sequencing and 1643 via whole-exome/genome sequencing). We also accessed the exome sequences of an additional 8069 individuals from non-cancer-related laboratories and public databanks as well as genetic results from the Catalogue of Somatic Mutations in Cancer (COSMIC) project. The mean allelic frequency observed in the controls was 0.0031, with higher occurrences in Central European populations (0.006/0.008). The prevalence of RET Y791F in the control databases was extremely high compared with the 40 known RET pathogenic mutations (P=0.00003), while no somatic occurrence has been reported in tumours. In this study, we report new, unrelated Brazilian individuals with germline RET Y791F-only: two tumour-free elderly controls; two individuals with sporadic MTC whose Y791F-carrying relatives did not show any evidence of tumours; and a 74-year-old phaeochromocytoma patient without MTC. Furthermore, we showed that the co-occurrence of Y791F with the strong RET C634Y mutation explains the aggressive MTC phenotypes observed in a large affected family that was initially reported as Y791F-only. Our literature review revealed that limited analyses have led to the misclassification of RET Y791F as a probable pathogenic variant and, consequently, to the occurrence of unnecessary thyroidectomies. The current study will have a substantial clinical influence, as it reveals, in a comprehensive manner, that RET Y791F only shows no association with MTC susceptibility.

The insulin-sensitivity sulphonylurea receptor variant is associated with thyrotoxic paralysis.

Thyrotoxicosis is the most common cause of the acquired flaccid muscle paralysis in adults called thyrotoxic periodic paralysis (TPP) and is characterised by transient hypokalaemia and hypophosphataemia under high thyroid hormone levels that is frequently precipitated by carbohydrate load. The sulphonylurea receptor 1 (SUR1 (ABCC8)) is an essential regulatory subunit of the ß-cell ATP-sensitive K(+) channel that controls insulin secretion after feeding. Additionally, the SUR1 Ala1369Ser variant appears to be associated with insulin sensitivity. We examined the ABCC8 gene at the single nucleotide level using PCR-restriction fragment length polymorphism (RFLP) analysis to determine its allelic variant frequency and calculated the frequency of the Ala1369Ser C-allele variant in a cohort of 36 Brazilian TPP patients in comparison with 32 controls presenting with thyrotoxicosis without paralysis (TWP). We verified that the frequency of the alanine 1369 C-allele was significantly higher in TPP patients than in TWP patients (61.1 vs 34.4%, odds ratio (OR)=3.42, P=0.039) and was significantly more common than the minor allele frequency observed in the general population from the 1000 Genomes database (61.1 vs 29.0%, OR=4.87, P<0.005). Additionally, the C-allele frequency was similar between TWP patients and the general population (34.4 vs 29%, OR=1.42, P=0.325). We have demonstrated that SUR1 alanine 1369 variant is associated with allelic susceptibility to TPP. We suggest that the hyperinsulinaemia that is observed in TPP may be linked to the ATP-sensitive K(+)/SUR1 alanine variant and, therefore, contribute to the major feedforward precipitating factors in the pathophysiology of TPP.