Constitutive RET tyrosine kinase activation in hereditary medullary thyroid cancer: clinical opportunities

Multiple endocrine neoplasia type 2 (MEN2) and RET specific modifications of the ACMG/AMP variant classification guidelines and impact on the MEN2 RET database

The Multiple Endocrine Neoplasia type 2 (MEN2) RET proto-oncogene database, originally published in 2008, is a comprehensive repository of all publicly available RET gene variations associated with MEN2 syndromes. The variant-specific genotype/phenotype information, age of earliest reported medullary thyroid carcinoma (MTC) onset, and relevant references with a brief summary of findings are cataloged. The ACMG/AMP 2015 consensus statement on variant classification was modified specifically for MEN2 syndromes and RET variants using ClinGen sequence variant interpretation working group recommendations and ClinGen expert panel manuscripts, as well as manuscripts from the American Thyroid Association Guidelines Task Force on Medullary Thyroid Carcinoma and other MEN2 RET literature. The classifications for the 166 single unique variants in the MEN2 RET database were reanalyzed using the MEN2 RET specifically modified ACMG/AMP classification guidelines (version 1). Applying these guidelines added two new variant classifications to the database (likely benign and likely pathogenic) and resulted in clinically significant classification changes (e.g., from pathogenic to uncertain) in 15.7% (26/166) of the original variants. Of those clinically significant changes, the highest percentage of changes, 46.2% (12/26), were changes from uncertain to benign or likely benign. The modified ACMG/AMP criteria with MEN2 RET specifications will optimize and standardize RET variant classifications.

Multiple endocrine neoplasia 2: an overview

This review article discusses the diagnosis and treatment of patients with multiple endocrine neoplasia type 2 (MEN2). The most common tumors associated with MEN2 are those of the parathyroid, thyroid, and adrenal glands. Additional manifestations include characteristic clinical phenotypes or features as described in the article. This review provides an overview of clinical manifestations, screening, diagnosis, treatment, and surveillance of patients with MEN2.

Polymorphisms Within the RET Proto-Oncogene and Risk of Sporadic Medullary Thyroid Carcinoma

Background: Sporadic medullary thyroid carcinoma (sMTC) is an uncommon neoplasia arising from the calcitonin-producing parafollicular cells of the thyroid. Previous studies evaluated whether single nucleotide polymorphisms (SNPs) within RET (a pivotal proto-oncogene for this disease) are associated with the risk for developing sMTC, but the results are inconclusive. Methods: In this work, we evaluated the association of RET-SNPs c.74-126G>T (rs2565206), p.Gly691Ser (rs1799939, G>A), p.Leu769 = (rs1800861, G>T), p.Ser836 = (rs1800862, C>T), and p.Ser904 = (rs1800863, C>G) (listed in the order of their chromosomal location) with sMTC. This is one of the largest case-control association studies carried out on sMTC, including 585 sMTC cases (negative for germline mutations within RET), 1529 patients affected by sporadic nonmedullary thyroid carcinoma (sNMTC), and 989 healthy controls, from central and southern Italy and collected in the period 2000-2017. Results: sNMTC patients showed similar genotype and allele frequencies compared with healthy controls. On the other hand, among sMTC patients, the T-allele of p.Leu769 = was less frequent (OR = 0.70 [CI 0.58-0.84], p = 1.9 × 10^-4) and rare homozygotes TT showed an OR = 0.32 ([CI 0.17-0.60], p = 2.3 × 10^-4). Moreover, a statistically significant excess of the haplotype 2 (characterized by the alleles T-G-G-C-C of the listed SNPs) was observed (p = 3.9 × 10^-3). The SNPs were not associated with the expression of RET mRNA, that is, they did not exert an effect in cis as quantitative trait locus (cis-eQTL). However, a strong eQTL association was found for p.Leu769 = and the neighboring gene CSGALNACT2 (p = 9.3 × 10^-50; effect-size = -0.65), whose function in cancer is unknown. Conclusions: This study shows that specific RET haplotypes, in particular haplotype 2 and the T-allele of p.Leu769 = , are associated with a reduced risk of sMTC in Italians.

A rare RET mutation in an Indian pedigree with familial medullary thyroid carcinoma

Familial medullary thyroid carcinoma (FMTC) is a variant of multiple endocrine neoplasia type 2 (MEN2) associated with the RET gene mutation. We report a rare RET mutation of c.2671T>G; p.Ser891Ala in Exon 15 of the RET gene in an Indian pedigree where seven family members out of 14 screened were found to be positive for the same. RET genetic analysis should be considered as an early approach in the diagnosis of medullary thyroid carcinoma (MTC) since it improves the prognosis and permits surveillance of other family members.

RET Proto-oncogene Gene Mutation Is Related to Cervical Lymph Node Metastasis in Medullary Thyroid Carcinoma

RET proto-oncogene (RET) mutations were proved to be related to the development of medullary thyroid carcinoma (MTC). We aimed to analyze the role of RET mutations in cervical lymph node metastasis in patients with MTC. Forty-nine patients with preoperatively diagnosed MTC by fine-needle aspiration cytology (FNAC) who underwent bilateral total thyroidectomy with cervical lymphadenectomy were included. Postoperative RET gene test and pathological analysis were performed with the surgical specimens; serum calcitonin (Ctn) and carcinoembryonic antigen (CEA) levels were tested pre- and postoperatively, to evaluate the association between RET mutations and cervical lymph node metastasis in MTC. In these 49 patients, the RET mutation rates of Exon 11, Exon 10, Exon 11&13, Exon 13, and Exon 16 were 20.4%, 4.1%, 38.8%, 22.4%, and 0%, respectively. The lymph node metastasis rates of patients with RET mutation in the central and lateral compartments were 71.4% and 64.3%, respectively, versus 28.6% and 14.3% of patients without RET mutation. The preoperative basal serum levels of Ctn (234.8 ± 188.4 vs. 44.4 ± 27.5, p < 0.01) and postoperative Ctn (49.8 ± 86.4 vs. 3.7 ± 2.2, p = 0.001) in MTC patients with RET mutations were significantly higher than those in MTC patients without RET mutation. In addition, the preoperative (50.2 ± 76.7 vs. 7.4 ± 6.8, p = 0.001) and postoperative serum levels of CEA (13.2 ± 19.5 vs. 1.3 ± 1.6, p < 0.01) in MTC patients with RET mutations were significantly higher than those in MTC patients without RET mutation (p < 0.05). RET mutation was related to cervical lymph node metastasis in patients with MTC, especially the mutation in Exon 11&13. Patients with RET mutation in Exon 11&13 might be regarded as the predictor for prophylactic ipsilateral total cervical lymphadenectomy even without clear evidence of lateral cervical lymph node metastasis.

Genotype-specific progression of hereditary medullary thyroid cancer

Although already 25 years into the genomic era, age-related progression of hereditary medullary thyroid cancer (MTC), the prevalence of which is estimated at one in 80,000 inhabitants, remains to be delineated for most unique RET (REarranged during Transfection) mutations. Included in this study were 567 RET carriers. The age-related progression of MTC across histopathological groups (normal thyroid/C-cell hyperplasia; node-negative MTC; node-positive MTC) was statistically significant for 13 unique RET mutations (p.Cys611Phe/c.1832G > T; p.Cys611Tyr; p.Cys618Ser/c.1852T > A; p.Cys620Arg; p.Cys634Arg; p.Cys634Phe; p.Cys634Ser; p.Cys634Tyr; p.Glu768Asp; p.Leu790Phe/c.2370G > T; p.Val804Met; p.Ser891Ala; p.Met918Thr), whereas two unique RET mutations (p.Cys618Phe; p.Cys634Gly) trended toward statistical significance. When grouped by mutational risk (highest; high; moderate-high; low-moderate; polymorphism), the age-related progression of MTC was significant for all four categories of RET mutations, which differed significantly across and within the three histopathological groups. For high, for moderate-high, and for low-moderate risk RET mutations, the age-related progression of MTC by mutated codon was broadly comparable across and within the three histopathological groups, and essentially unaffected by the amino acid substitutions examined. These data argue in favor of splitting the American Thyroid Association's moderate-risk category into moderate-high and low-moderate risk categories, while emphasizing the need to contradistinguish the latter from rare nonpathogenic polymorphisms.

Advances in risk-oriented surgery for multiple endocrine neoplasia type 2

Genetic association studies hinge on definite clinical case definitions of the disease of interest. This is why more penetrant mutations were overrepresented in early multiple endocrine neoplasia type 2 (MEN2) studies, whereas less penetrant mutations went underrepresented. Enrichment of genetic association studies with advanced disease may produce a flawed understanding of disease evolution, precipitating far-reaching surgical strategies like bilateral total adrenalectomy and 4-gland parathyroidectomy in MEN2. The insight into the natural course of the disease gleaned over the past 25 years caused a paradigm shift in MEN2: from the removal of target organs at the expense of greater operative morbidity to close biochemical surveillance and targeted resection of adrenal tumors and hyperplastic parathyroid glands. The lead time provided by early identification of asymptomatic MEN2 carriers under biochemical surveillance delimits a 'window of opportunity', within which (i) pre-emptive total thyroidectomy alone is adequate, circumventing morbidity attendant to central node dissection; (ii) subtotal 'tissue-sparing' adrenalectomy is sufficient, trading the risk of steroid dependency for the risk of a second pheochromocytoma in the adrenal remnant and (iii) parathyroidectomy is limited to enlarged glands, trading the risk of postoperative hypoparathyroidism for the risk of leaving behind hyperactive parathyroid glands. Future research should delineate further the mutation-specific, age-dependent penetrance of pheochromocytoma and primary hyperparathyroidism to refine the risk-oriented approach to MEN2. The sweeping changes in the management of MEN2 since the new millenium hold the hope that death and major morbidity from this uncommon disease can be eliminated in our lifetime.

Medullary thyroid carcinoma: a review on ethical considerations in treatment of children

Thyroid carcinoma is the most common malignancy of the endocrine system and it accounts approximately 1%-3% of all human cancers. Among the three subtypes of thyroid cancers, medullary thyroid carcinoma (MTC) is the most common cause of death in patients with multiple endocrine neoplasia (MEN) type 2A (MEN2A), MEN type 2B (MEN2B) and familial medullary thyroid carcinoma (FMTC). Generally, MTC accounts for up to 10% of all types of thyroid cancers. It is one of the aggressive forms of thyroid carcinoma which is manifested in childhood ages more than adults, and it comprises about 17% of all pediatric thyroid cancer. Like the other cancers, prevention of MTC is easier than its cure. In the recent decades (from 1993) the diagnosis of asymptomatic child carrying RET mutations in the affected families by MTC, has been provided by genetic screening, and prophylactic thyroidectomy is an efficacy therapeutic procedure. On the one hand, according to near the complete penetrance of the disease and its onset in the early years of life, it is required to accelerate the protection of at-risk children with relative affected by MTC and on the other hand, there are several obstructions to MTC treatment including: 1) the proband's refusal to disclose the RET mutation genetic testing results, 2) children's vulnerability because of their inability to participate in the informed consent, and 3) the existence of conflict between physicians and children's guardian. In this review article, the recommendations and ethical issues of MTC treatment in asymptomatic and at-risk children have been summarized.

Distribution of RET Mutations and Evaluation of Treatment Approaches in Hereditary Medullary Thyroid Carcinoma in Turkey

OBJECTIVE

This retrospective multicenter study, centrally conducted and supported by the Society of Endocrinology and Metabolism of Turkey, aimed to evaluate the impact of free RET proto-oncogene testing in medullary thyroid carcinoma (MTC) patients. Surgical timing, adequacy of the treatment, and frequency of prophylactic thyroidectomy (PTx) in mutation carriers were also assessed.

METHODS

Genetic testing for MTC and pheochromocytoma was conducted between July 2008 and January 2012 in 512 patients. Application forms and RET mutation analyses of these patients whose blood samples were sent from various centers around Turkey were assessed retrospectively. An evaluation form was sent to the physicians of the eligible 319 patients who had confirmed sporadic MTC, familial MTC (FMTC), multiple endocrine neoplasia type 2 (MEN2), or who were mutation carriers. Physicians were asked to give information about the surgical history, latest calcitonin levels, morbidity, mortality, genetic screening, and PTx among family members. Twenty-five centers responded by filling in the forms of 192 patients.

RESULTS

Among the 319 patients, RET mutation was detected in 71 (22.3%). Cys634Arg mutation was the most prevalent mutation (43.7%), followed by Val804Met in 18 patients (25.4%), and Cys634Tyr in 6 patients (8.5%). Among 192 MTC patients, the diagnosis was sporadic MTC in 146 (76.4%), FMTC in 14 (7.3%), MEN2A in 15 patients (7.9%), and MEN2B in one patient. The number of mutation carriers among 154 apparently sporadic MTC patients was 8 (5.2%). Ten patients were submitted to PTx out of twenty-four mutation carriers at a mean age of 35±19 years.

CONCLUSION

Turkish people have a similar RET proto-oncogene mutation distribution when compared to other Mediterranean countries. Despite free RET gene testing, the number of the PTx in Turkey is limited and relatively late in the life span of the carriers. This is mainly due to patient and family incompliance and incomplete family counselling.

The rare intracellular RET mutation p.S891A in a Chinese Han family with familial medullary thyroid carcinoma

We report intracellular RET mutation in a Han Chinese pedigree with familial medullary thyroid carcinoma (FMTC). Direct sequencing of RET proto-oncogene identified a missense c.2671T greater than G (p.S891A) mutation in 6 of 14 family members. The single nucleotide polymorphisms c. 135A greater than G (p.A45A), IVS4 + 48A greater than G, c. 1296A greater than G (p.A432A), c. 2071G greater than A (p.G691S), c. 2307T greater than G (p.L769L) and a variant c. 833C greater than A (p.T278N) were also found in 6 carriers. Among 5 of the 6 carriers presented medullary thyroid carcinoma (MTC) as an isolated clinical phenotype, with elevated basal serum calcitonin (Ct). Two underwent non-normative thyroidectomy either two or four times without physician awareness or diagnosis of this disease at initial treatment, but with elevated Ct. One with elevated pre-Ct accepted total thyroidectomy (TT) with modified bilateral neck dissection (MBiND), and whose seventh posterior rib MTC metastases was confirmed 5 months after surgery. Moreover, results of two affected individuals with elevated Ct were reduced to normal after TT with MBiND or prophylactic VI compartmental dissection. However, only another carrier with the variant p.T278N had slightly elevated Ct rejected surgery and was strictly monitored. Given these case results, we suggest that screening of RET and pre-surgical Ct levels in the management of MTC patients is essential for earlier diagnosis and more normative initial treatment, that FMTC patients with cervical lymph nodes metastases may be cured by TT with MBiND, and that prophylactic VI compartmental dissection should be avoided when Ct levels are low.

Progression of medullary thyroid cancer in RET carriers of ATA class A and C mutations

CONTEXT

There is no histopathological or radiological information on the natural course of tumor growth and lymph node metastasis in medullary thyroid cancer (MTC).

OBJECTIVE

This investigation aimed at determining annual rates of tumor growth and lymph node metastasis in hereditary MTC at the surgical pathology level.

DESIGN

This was a retrospective analysis.

SETTING

The setting was a tertiary referral center.

PATIENTS

Included were 172 carriers of American Thyroid Association (ATA) class C (95 patients) and class A rearranged during transfection (RET) mutations (77 patients) with MTC.

INTERVENTION

The intervention was compartment-oriented surgery.

MAIN OUTCOME MEASURES

Comparisons of means between index and nonindex patients yielded incremental primary tumor diameter and incremental number of lymph node metastases, which were divided by incremental patient age at tissue diagnosis.

RESULTS

Annual primary tumor growth was 0.4-0.5 mm in node-negative carriers of ATA class A and C mutations. In node-positive carriers, annual primary tumor growth was 2.6 mm (ATA class C mutations) and 1.2 mm (ATA class A mutations), more than 6-fold (2.6 vs 0.4 mm) and more than 2-fold greater (1.2 vs 0.5 mm) than in their node-negative peers. Node-positive carriers revealed an annual rate of lymph node metastasis of 0.6-0.7 nodes independent of ATA class.

CONCLUSIONS

Small MTCs may take longer than 10 years to become big enough to visualize on imaging. These slow growth rates highlight the importance of following up on patients for very long time periods to uncover at least some tumoral sources of persistent calcitonin production.

The value of genetic screening in medullary thyroid cancer

Medullary thyroid cancer (MTC) accounts for ~10% of thyroid carcinomas and occurs in sporadic and hereditary forms. Early diagnosis significantly impacts the clinical course, management and outcome of the disease. The identification of germline-activating mutations of the rearranged during transfection oncogene in patients with hereditary MTC led to significant progress in the diagnostic and therapeutic approach, thus improving the quality of care provided, and consequently, disease prognosis. In the present review, various aspects of genetic screening (GS) in MTC will be covered, which elucidate the value of GS in guiding clinical decision making, therapy selection and appropriate genetic counseling of the affected families. GS should be offered to every MTC patient, based on the personal and family medical history, to allow optimal clinical management and follow-up.

The rare intracellular RET mutation p.Ser891Ala in an apparently sporadic medullary thyroid carcinoma: a case report and review of the literature

Medullary thyroid carcinoma (MTC) is a malignant tumor originating from parafollicular C-cells and accounts for 4-10% of all thyroid carcinomas. MTC develops in either sporadic (75%) or hereditary form (25%). Mutations in the RET proto-oncogene are responsible for hereditary MTC and the rate of heritable disease among apparently sporadic MTC (sMTC) cases varies from 6 to 15%. RET genetic testing is now considered fundamental in MTC management but the extent of the molecular analysis required to exclude inherited disease is still controversial. While the screening of all known mutation loci is recommended by some authors, the high costs associated with a full analysis should be also taken into consideration. Here, we illustrate and discuss this controversial issue by reporting a patient who present all characteristic features of sMTC, and in whom a standard genetic analysis by restriction enzyme restriction excluded hereditary disease. Nevertheless, an extensive molecular analysis that included all codons was prompted by the diagnosis of thyroid neoplasm in a patient's sister, and identified the rare intracellular RET p.Ser891Ala mutation.

[Medullary thyroid carcinoma in children]

Medullary thyroid carcinoma (MTC) is rare in children. MTC is almost always inherited and occurs as part of a multiple endocrine neoplasia type 2A and B, due to germline mutation in the RET proto-oncogene. MTC in the pediatric population is most often diagnosed in the course of a familial genetic investigation. But when the child is the proband, a de novo mutation is most often founded. The main aim is to treat MTC before extrathyroidal extension occurs because when distant metastases are present, it is rarely curable. Treatment is based on total thyroidectomy with cervical lymph node dissection.

Molecular epidemiology of multiple endocrine neoplasia 2: implications for RET screening in the new millenium

OBJECTIVE

Twenty years ago, the groundbreaking discovery that rearranged during transfection (RET) mutations underlie multiple endocrine neoplasia 2 (MEN2) and familial medullary thyroid cancer (FMTC) ushered in the era of personalized medicine. MEN2-associated signs, taking time to manifest, can be subtle. This study sought to clarify to what extent conventional estimates of 1:200 000-500 000 underestimate the incidence of RET mutations in the population.

DESIGN

Included in this retrospective investigation were 333 RET carriers born between 1951 and 2000 and operated on at the largest German surgical referral center (286 carriers) or elsewhere (47 carriers).

METHODS

To estimate the incidence of RET mutations, the number of RET carriers born in Germany in five decades (1951-1960, 1961-1970, 1971-1980, 1981-1990, and 1991-2000) was divided by the corresponding number of German live births.

RESULTS

Owing to improved diagnosis and capture of FMTC and MEN2 patients, minimum incidence estimates increased over time: overall from 5.0 (1951-1960) to 9.9 (1991-2000) per million live births and year (P=0.008), and by American Thyroid Association/ATA class from 1.7 to 3.7 for ATA class C (P=0.008); from 1.8 to 2.7 for ATA class A (P=0.017); from 1.5 to 2.2 for ATA class B (P=0.20); and from 0 to 1.4 for ATA class D mutations per million live births and year (P=0.008). Based on 1991-2000 incidence estimates the prevalence in Germany is ∼1:80 000 inhabitants.

CONCLUSIONS

The molecular minimum incidence estimate of ≈1:100 000 was two- to fivefold greater than conventional estimates of 1:200 000-500 000.

Hereditary medullary thyroid carcinoma: the management dilemma

Hereditary medullary thyroid carcinoma (hereditary MTC) is a rare malignancy, accounting for 25-30% of all MTC. It occurs as part of multiple endocrine neoplasia type 2 (MEN 2). Autosomal dominant gain-of-function mutations in the RET proto-oncogene is the cause of the disease, in which the common mutations are codons 609, 611, 618, 620, 630, 634 and 918. In recent years, the spectrum of RET gene mutations has changed. The classical mutations reduced, whereas the less aggressive mutations increased. Hereditary MTC is a time-dependent disease. Stages of the disorder at diagnosis can significantly influence survival rates. Based on the genotype-phenotype, RET mutations have been classified into four risk levels by American Thyroid Association (ATA) at 2009. The classification system guides the hereditary MTC management, including risk assessment, biochemical screenings and surgical intervention. Though the application of genetic testing and codon-specific phenotypes in hereditary MTC diagnosis is effective with high accuracy, there are some difficulties in implementing RET gene testing as a routine for MTC diagnosis. And most of carriers with RET mutations did not undergo thyroidectomy at the age recommended by the ATA guidelines. The aim of the study is to review the hereditary MTC and discuss the management dilemma.

Clinical relevance of RET variants G691S, L769L, S836S and S904S to sporadic medullary thyroid cancer

BACKGROUND

Based on reports of higher frequencies among patients with sporadic medullary thyroid cancer (MTC) relative to external controls, the RET (REarranged during Transfection) variants G691S, L767L, S836S and S904S have been considered disease modifiers, suggesting greater lifetime risks of MTC. Other studies, employing different external controls, failed to confirm this association. Using a complementary approach, this study aimed at exploring differences in clinico-pathological characteristics among patients with sporadic MTC carrying no (wildtype), one (heterozygotes) or both (homozygotes) homologue RET variants in the germline, with wildtype cases acting as internal controls.

METHODS

Included in this investigation were 150 patients with complete genetic information on G691S, L769L, S836S and S904S RET alleles operated on for sporadic MTC at a tertiary referral centre.

RESULTS

Not one statistically significant dose-response relationship was identified between any RET variant (wildtype vs RET heterozygotes vs homologue RET homozygotes) and patient age at MTC diagnosis, gender, primary tumour size, extrathyroidal extension, numbers of involved and removed lymph nodes, or distant metastasis. L769L and S836S homozygotes, unlike G691S and S904S homozygotes, were either rare or absent, limiting the analyses to comparisons of heterozygosity versus wildtype. On time-to-event analysis, G691S, L769L, S836S or S904S carriers and noncarriers developed MTC at similar rates.

CONCLUSIONS

In carriers and noncarriers of the RET variants G691S, L767L, S836S and S904S, sporadic MTC appeared clinically and pathologically indistinguishable. This observation, along with the inconclusive evidence of previous association studies, calls for larger longitudinal association studies with age- and sex-matched external controls and additional functional studies of RET biology.

RET haplotype, not linked to the C620R activating mutation, associated with Hirschsprung disease in a novel MEN2 family

Hirschsprung disease is a congenital form of aganglionic megacolon that results from cristopathy. Hirschsprung disease usually occurs as a sporadic disease, although it may be associated with several inherited conditions, such as multiple endocrine neoplasia type 2. The rearranged during transfection (RET) proto-oncogene is the major susceptibility gene for Hirschsprung disease, and germline mutations in RET have been reported in up to 50% of the inherited forms of Hirschsprung disease and in 15-20% of sporadic cases of Hirschsprung disease. The prevalence of Hirschsprung disease in multiple endocrine neoplasia type 2 cases was recently determined to be 7.5% and the cooccurrence of Hirschsprung disease and multiple endocrine neoplasia type 2 has been reported in at least 22 families so far. It was initially thought that Hirschsprung disease could be due to disturbances in apoptosis or due to a tendency of the mutated RET receptor to be retained in the Golgi apparatus. Presently, there is strong evidence favoring the hypothesis that specific inactivating haplotypes play a key role in the fetal development of congenital megacolon/Hirschsprung disease. In the present study, we report the genetic findings in a novel family with multiple endocrine neoplasia type 2: a specific RET haplotype was documented in patients with Hirschsprung disease associated with medullary thyroid carcinoma, but it was absent in patients with only medullary thyroid carcinoma. Despite the limited number of cases, the present data favor the hypothesis that specific haplotypes not linked to RET germline mutations are the genetic causes of Hirschsprung disease.

Multiple endocrine neoplasia type 2: achievements and current challenges

Incremental advances in medical technology, such as the development of sensitive hormonal assays for routine clinical care, are the drivers of medical progress. This principle is exemplified by the creation of the concept of multiple endocrine neoplasia type 2, encompassing medullary thyroid cancer, pheochromocytoma, and primary hyperparathyroidism, which did not emerge before the early 1960s. This review sets out to highlight key achievements, such as joint biochemical and DNA-based screening of individuals at risk of developing multiple endocrine neoplasia type 2, before casting a spotlight on current challenges which include: (i) ill-defined upper limits of calcitonin assays for infants and young children, rendering it difficult to implement the biochemical part of the integrated DNA-based/biochemical concept; (ii) our increasingly mobile society in which different service providers are caring for one individual at various stages in the disease process. With familial relationships disintegrating as a result of geographic dispersion, information about the history of the origin family may become sketchy or just unavailable. This is when DNA-based gene tests come into play, confirming or excluding an individual's genetic predisposition to multiple endocrine neoplasia type 2 even before there is any biochemical or clinical evidence of the disease. However, the unrivaled molecular genetic progress in multiple endocrine neoplasia type 2 does not come without a price. Screening may uncover unknown gene sequence variants representing either harmless polymorphisms or pathogenic mutations. In this setting, functional characterization of mutant cells in vitro may generate helpful ancillary evidence with regard to the pathogenicity of gene variants in comparison with established mutations.

Genetic alterations in medullary thyroid cancer: diagnostic and prognostic markers

Medullary thyroid carcinoma (MTC) is a rare calcitonin producing neuroendocrine tumour that originates from the parafollicular C-cells of the thyroid gland. The RET proto-oncogene encodes the RET receptor tyrosine kinase, with consequently essential roles in cell survival, differentiation and proliferation. Somatic or germline mutations of the RET gene play an important role in this neoplasm in development of sporadic and familial forms, respectively. Genetic diagnosis has an important role in differentiating sporadic from familiar MTC. Furthermore, depending on the location of the mutation, patients can be classified into risk classes. Therefore, genetic screening of the RET gene plays a critical role not only in diagnosis but also in assessing the prognosis and course of MTC.

In silico and in vitro analysis of rare germline allelic variants of RET oncogene associated with medullary thyroid cancer

Germline and somatic RET oncogene mutations are found in 98% hereditary and 40% sporadic medullary thyroid carcinomas. Our aim was to analyse by in silico and in vitro assays the transforming activity of six rare RET mutations (T338I, V648I, M918V, A883T, S904F and M848T). Six known RET mutations were used as controls. The in silico analysis showed the highest score value (i.e. 65) for S904F, M848T, M918T and C634R, whereas L790F, G691S, T338I and V648I had 0 score. Intermediate score values were obtained by A883T (score=55), M918V, V804M and Y791F (score=15). The in vitro focus formation assay showed that cells transfected with S904F, M918T, M848T or C634R generated the largest number of focus formation units (FFU). Intermediate numbers of FFU were observed in cells transfected with M918V, V804M, Y791F or A883T, while cells transfected with L790F, G691S, T338I or V648I showed a number of FFU similar to control cells. A positive correlation between the in silico score and in vitro FFU was found (P=0.0005). Only cells transfected with M918T or C634R grew faster and generated higher number of colonies in soft agar than control cells. However, the cells that were transfected with V804M produced an intermediate number of colonies. In conclusion, two of the six rare RET mutations, S904F and M848T possessed a relatively high transforming activity but a low aggressiveness; the other four mutations T338I, V648I, M918V and A883T were low or non-transforming, and their ability to induce tumoural transformation might be related to particular genetic conditions.

Management of medullary thyroid carcinoma and MEN2 syndromes in childhood

Medullary thyroid carcinoma (MTC) and the multiple endocrine neoplasia (MEN) type 2 syndromes are rare but important endocrine diseases that are increasingly managed by pediatric providers. MTC is generally associated with a favorable prognosis when diagnosed during childhood, where it frequently occurs secondary to activating mutations in the RET proto-oncogene and arises from pre-existing C-cell hyperplasia. MEN2A accounts for 90-95% of childhood MTC cases and is most commonly due to mutations in codon 634 of RET. MEN2B is associated with the most aggressive clinical presentation of MTC and is almost always due to the Met918Thr mutation of RET. Surgery is the primary treatment and only chance of cure, although the advent of targeted therapies seems to be improving progression-free survival in advanced cases. Since the discovery of the role of RET in MEN2A, considerable advances in the management of this syndrome have occurred, and most of the children with MEN2A who have undergone early thyroidectomy will now lead full, productive lives. Strong genotype-phenotype correlations have facilitated the development of guidelines for interventions. Contemporary approaches for deciding the appropriate age at which surgery should take place incorporate data from ultrasonography and calcitonin measurements in addition to the results of genotyping. To optimize care and to facilitate ongoing research, children with MTC and the MEN2 syndromes are optimally treated at tertiary centers with multidisciplinary expertise.

Multiple endocrine neoplasias: advances and challenges for the future

Several important advances have been made over the last 2 years, since the last international workshop on multiple endocrine neoplasias (MENs) that was held in Marseilles, France (MEN2006). The series of articles that are included in this issue summarize the most important of these advances as they were presented in Delphi, Greece, during the 11th International Workshop on MENs, September 25-27, 2008 (MEN2008). This editorial summarizes some of these advances: the identification of the AIP, and the PDE11A and PDE8B genes by genome-wide association (GWA) studies as predisposing genes for pituitary and adrenal tumours, respectively, the discovery of p27 mutations in a new form of MEN similar to MEN type 1 (MEN 1) that is now known as MEN 4, the molecular investigations of Carney triad (CT), a disorder that associates paragangliomas (PGLs), gastrointestinal stromal tumour (GISTs), and pulmonary chondromas (PCH) with pheochromocytomas and adrenocortical adenomas and other lesions, and the molecular elucidation of the association of GISTs with paragangliomas (Carney-Stratakis syndrome) that is now known to be because of SDHB, SDHC, and SDHD mutations. Molecular investigations in Carney complex (another MEN also described by Dr. Carney, who during the meeting, along with Dr. Charles E. ('Gene') Jackson was honoured for his life-long and many contributions to the field) have also revealed the role of cyclic AMP signalling in tumorigenesis. As our knowledge of the molecular causes of MENs increases, the challenge is to translate these discoveries in better treatments for our patients. Indeed, new advances in the preventive diagnosis and molecular treatment of MEN 1 and MEN 2, respectively, continued unabated, and an update on this front was also presented at MEN2008 and is included in this issue.