A mutation in the RET proto-oncogene associated with multiple endocrine neoplasia type 2B and sporadic medullary thyroid carcinoma

KIF5B-RET fusions in Chinese patients with non-small cell lung cancer

BACKGROUND

It has been established that "ret proto-oncogene" (RET) fusions are oncogenic drivers in non-small cell lung cancer (NSCLC). The prevalence and clinicopathologic characteristics of RET fusions in Chinese patients with NSCLC remain unclear. The objective of the current study was to determine the prevalence and clinicopathologic characteristics of KIF5B-RET fusions (fusions of the RET and kinesin family member 5B [KIF5B] genes) in Chinese patients with NSCLC.

METHODS

The authors screened for KIF5B-RET fusions in 392 patients with NSCLC using multiplex real-time polymerase chain reaction assay and validated all positive samples using direct sequencing. The relations between KIF5B-RET fusions and clinicopathologic characteristics were analyzed.

RESULTS

In total, 6 patients (1.5%) were identified who harbored KIF5B-RET fusions. Of these, 4 had adenocarcinoma, 1 had a malignant neuroendocrine tumor, and 1 had squamous cell carcinoma. All patients who were positive for a KIF5B-RET fusion were never-smokers. There was no statistically significant difference in age, sex, smoking status, pathologic stage, or histologic type between patients with and without KIF5B-RET fusions. Patients without KIF5B-RET fusions had a better prognosis than those with KIF5B-RET fusions (median survival, 52.6 months vs 21.0 months; P = .06), with a hazard ratio of 2.398 (95% confidence interval, 0.982-5.856; P = .055) on multivariate analysis. Disease stage (hazard ratio, 2.879) and younger age (<65 years; hazard ratio, 1.485) were identified as independent prognostic factors for better survival.

CONCLUSIONS

KIF5B-RET fusions were quite rare, with a prevalence of approximately 1.5% in Chinese patients with NSCLC, and they were a little more common in patients with adenocarcinoma than in those with squamous carcinoma (1.73% vs 0.84%). In addition, KIF5B-RET fusions also existed in patients with low-grade malignant neuroendocrine tumors.

Structure and physiology of the RET receptor tyrosine kinase

The identification of the ret oncogene by Masahide Takahashi and Geoffrey Cooper in 1985 was both serendipitous and paradigmatic ( Takahashi et al. 1985). By transfecting total DNA from a human lymphoma into mouse NIH3T3 cells, they obtained one clone, which in secondary transformants yielded more than 100-fold improvement in transformation efficiency. Subsequent investigations revealed that the ret oncogene was not present as such in the primary lymphoma, but was derived by DNA rearrangement during transfection from normal human sequences of the ret locus. At the time, activation by DNA rearrangement had not been previously described for a transforming gene with the NIH3T3 transfection assay. The discovery of ret opened a field of study that has had a profound impact in cancer research, developmental biology, and neuroscience, and that continues to yield surprises and important insights to this day.

Phosphotyrosine signaling proteins that drive oncogenesis tend to be highly interconnected

Mutation and overexpression of receptor tyrosine kinases or the proteins they regulate serve as oncogenic drivers in diverse cancers. To better understand receptor tyrosine kinase signaling and its link to oncogenesis, we used protein microarrays to systematically and quantitatively measure interactions between virtually every SH2 or PTB domain encoded in the human genome and all known sites of tyrosine phosphorylation on 40 receptor tyrosine kinases and on most of the SH2 and PTB domain-containing adaptor proteins. We found that adaptor proteins, like RTKs, have many high affinity bindings sites for other adaptor proteins. In addition, proteins that drive cancer, including both receptors and adaptor proteins, tend to be much more highly interconnected via networks of SH2 and PTB domain-mediated interactions than nononcogenic proteins. Our results suggest that network topological properties such as connectivity can be used to prioritize new drug targets in this well-studied family of signaling proteins.

Genetics of neural crest and neurocutaneous syndromes

Neural crest progenitor cells are identified at the lateral margins of the neural placode at the time of gastrulation. With folding of the placode, these precursors are brought to the dorsal midline of the neural tube at the site of closure, become committed to neural crest lineage and almost immediately migrate peripherally to various predetermined sites in the body and then differentiate as a variety of cellular types in all three of the traditional "germ layers." All of these processes of migration and differentiation of neural crest are precisely genetically programed, temporally and spatially, by a variety of genes. Primary neurocutaneous syndromes are all very different diseases with different genetic mutations, but the unifying factor amongst them is that all are neurocristopathies and can be explained as such, including the tumor-suppressor function of several of these genes, especially those of neurofibromatosis 1 and 2 and tuberous sclerosis. This chapter reviews the principal genes that program neural crest development and also are documented, implicated, or suspected in the pathogenesis of neurocutaneous syndromes. Recent genetic discoveries are noted in epidermal nevus syndrome, including Proteus syndrome and their association with hemimegalencephaly and congenital infiltrating lipomatosis of the face.

Molecular diagnosis of genodermatoses

The progress of molecular genetics helps clinicians to prove or exclude a suspected diagnosis for a vast and yet increasing number of genodermatoses. This leads to precise genetic counselling, prenatal diagnosis and preimplantation genetic haplotyping for many inherited skin conditions. It is also helpful in such occasions as phenocopy, late onset and incomplete penetrance, uniparental disomy, mitochondrial inheritance and pigmentary mosaicism. Molecular methods of two genodermatoses are explained in detail, i.e. genodermatoses with skin fragility and neurofibromatosis type 1.

Building a brain in the gut: development of the enteric nervous system

The enteric nervous system (ENS), the intrinsic innervation of the gastrointestinal tract, is an essential component of the gut neuromusculature and controls many aspects of gut function, including coordinated muscular peristalsis. The ENS is entirely derived from neural crest cells (NCC) which undergo a number of key processes, including extensive migration into and along the gut, proliferation, and differentiation into enteric neurons and glia, during embryogenesis and fetal life. These mechanisms are under the molecular control of numerous signaling pathways, transcription factors, neurotrophic factors and extracellular matrix components. Failure in these processes and consequent abnormal ENS development can result in so-called enteric neuropathies, arguably the best characterized of which is the congenital disorder Hirschsprung disease (HSCR), or aganglionic megacolon. This review focuses on the molecular and genetic factors regulating ENS development from NCC, the clinical genetics of HSCR and its associated syndromes, and recent advances aimed at improving our understanding and treatment of enteric neuropathies.

Absence of the RET+3:T allele in the MTC patients

The mutations of the RET proto-oncogene contributes to the development of MTC by increasing the activity of the receptor encoded by this gene. Variant T of polymorphism rs2435357 located in the enhancer of the RET gene reduces the enhancer's activity. The opposite effects of rs2435357 and the mutations causing medullary thyroid carcinoma resulted in the investigation of the status of this polymorphism in patients with MTC. In our study, we compared the frequency of polymorphism rs2435357 in the group of 48 MTC patients with its frequency in Polish population. The frequency of heterozygotes C/T at rs2435357 reached almost 12% (18/152) for the Polish population, in contrast to the group of MTC patients where not even a single T allele was found. The frequency difference is statistically significant. This observation might indicate that the presence of the heterozygous T allele at rs2435357 may be associated with the inhibition of medullary thyroid carcinoma development.

AZD1480 blocks growth and tumorigenesis of RET- activated thyroid cancer cell lines

Persistent RET activation is a frequent event in papillary thyroid carcinoma (PTC) and medullary thyroid carcinoma (MTC). In these cancers, RET activates the ERK/MAPK, the PI3K/AKT/mTOR and the JAK/STAT3 pathways. Here, we tested the efficacy of a JAK1/2- inhibitor, AZD1480, in the in vitro and in vivo growth of thyroid cancer cell lines expressing oncogenic RET. Thyroid cancer cell lines harboring RET/PTC1 (TPC-1), RET M918T (MZ-CRC1) and RET C634W (TT) alterations, as well as TPC-1 xenografts, were treated with JAK inhibitor, AZD1480. This inhibitor led to growth inhibition and/or apoptosis of the thyroid cancer cell lines in vitro, as well as to tumor regression of TPC-1 xenografts, where it efficiently blocked STAT3 activation in tumor and stromal cells. This inhibition was associated with decreased proliferation, decreased blood vessel density, coupled with increased necrosis. However, AZD1480 repressed the growth of STAT3- deficient TPC-1 cells in vitro and in vivo, demonstrating that its effects in this cell line were independent of STAT3 in the tumor cells. In all cell lines, the JAK inhibitor reduced phospho-Y1062 RET levels, and mTOR effector phospho-S6, while JAK1/2 downregulation by siRNA did not affect cell growth nor RET and S6 activation. In conclusion, AZD1480 effectively blocks proliferation and tumor growth of activated RET- thyroid cancer cell lines, likely through direct RET inhibition in cancer cells as well as by modulation of the microenvironment (e.g. via JAK/phospho-STAT3 inhibition in endothelial cells). Thus, AZD1480 should be considered as a therapeutic agent for the treatment of RET- activated thyroid cancers.

Advances in molecular genetics of Hirschsprung's disease

Hirschsprung's disease (HSCR) is a developmental disorder of the enteric nervous system, which occurs due to the failure of neural crest cells to fully colonize the gut during embryonic development. It is characterized by the absence of the enteric ganglia in a variable length of the intestine. Substantial progress has been made in understanding the genetic basis of HSCR with the help of advanced genetic analysis techniques and animal models. More than 11 genes have been found to be involved in the pathogenesis of HSCR. The RET gene is the most important susceptibility gene involved in HSCR with both coding and non- coding sequence mutations. Due to phenotypic diversity and genetic complexity observed in HSCR, mutational analysis has limited practical value in genetic counseling and clinical practice. In this review, we discuss the progress that has been made in understanding the molecular genetics of HSCR and summarize the currently identified genes as well as interactions between pathways and gene-modifying loci in HSCR.

Genetic alterations in a primary medullary thyroid carcinoma and its lymph node metastasis in a patient with 15 years follow-up

Background

Association between DNA alterations and clinical parameters as recurrence, survival or prognosis has been found in a variety of tumors. A clear association between Medullary Thyroid Carcinoma (MTC) and RET oncogene mutation has been accepted. Specifically M918T RET mutation represents the main genetic event in most cases of sporadic MTC (SMTC) and limited chromosomal alterations analyses have been performed.

Methods

In the present work, a comparative genomic hybridization (CGH) study was performed using DNA from a primary tumor in a M918T RET mutation-positive SMTC patient and from its lymph node metastasis to investigate additional genetic alterations. We studied a patient with 15 years of follow-up and persistence of disease, confirmed by periodical elevated serum calcitonin (CT) levels.

Results

Only 3 chromosomal imbalances were identified in the primary tumor, gain of 18p, and loss of 6p and 16p region, whereas 25 chromosomal imbalances were identified in the metastasis (9 gains and 16 losses).

Conclusion

The chromosomal changes 6p-, 16p-, 18p + could determine in part the oncogenic phenotype in the primary M918T RET positive tumor and probably related to persistence of high serum CT levels in this patient. The additional chromosomal changes observed could be related to the metastasis phenotype. We suggest that some genes mapped at 6p, 16p and 18p chromosomal regions, could act as genes associated to cancer and could be related to persistent SMTC and good prognosis.

Virtual slides

The virtual slide(s) for this article can be found here: http://www.diagnosticpathology.diagnomx.eu/vs/1720753793691097

Low prevalence of the somatic M918T RET mutation in micro-medullary thyroid cancer

BACKGROUND

The prevalence of RET somatic mutations in sporadic medullary thyroid cancer (MTCs) is ∼40%-50%, and the most frequent somatic mutation is M918T. RET-positive MTCs have been demonstrated to have a more advanced stage at diagnosis and a worse outcome.

AIMS

The aim of the present work was to compare the prevalence of RET somatic mutations in sporadic microMTCs (<1 cm) and in larger MTCs.

PATIENTS

We analyzed the M918T RET point mutation in 160 sporadic MTC cases. Tumors were classified according to their size: group A, <1 cm; group B, >1 and <2 cm; group C, >2 and <3 cm; and group D, >3 cm.

RESULTS

The overall prevalence of the somatic M918T RET mutation was 19.4% (31/160). RET mutations were distributed differently among the four groups. The prevalence was 11.3% (6/53) in group A, 11.8% (8/68) in group B, 31.8% (7/22) in group C, and 58.8% (10/17) in group D, exhibiting an increase with increasing size of the tumor. When comparing the prevalence of mutations in the four groups, we found a lower prevalence in microMTCs (p<0.0001).

CONCLUSIONS

The overall prevalence of RET somatic mutations was lower than expected, and the prevalence of the somatic M918T RET mutation was significantly lower in microMTCs than in larger tumors. To explain this finding, we can hypothesize either that other oncogene(s) might be responsible for the majority of microMTC, thus identifying a tumor subset, or that the RET mutation might, or might not, occur later during tumor progression.

Germline gain-of-function mutations of ALK disrupt central nervous system development

Neuroblastoma (NB) is a frequent embryonal tumor of sympathetic ganglia and adrenals with extremely variable outcome. Recently, somatic amplification and gain-of-function mutations of the anaplastic lymphoma receptor tyrosine kinase (ALK) gene, either somatic or germline, were identified in a significant proportion of NB cases. Here we report a novel syndromic presentation associating congenital NB with severe encephalopathy and abnormal shape of the brainstem on brain MRI in two unrelated sporadic cases harboring de novo, germline, heterozygous ALK gene mutations. Both mutations are gain-of-function mutations that have been reported in NB and NB cell lines. These observations further illustrate the role of oncogenes in both tumour predisposition and normal development, and shed light on the pleiotropic and activity-dependent role of ALK in humans. More generally, missing germline mutations relative to the spectrum of somatic mutations reported for a given oncogene may be a reflection of severe effects during embryonic development, and may prompt mutation screening in patients with extreme phenotypes.

Role of vandetanib in the management of medullary thyroid cancer

Traditionally available treatments, like cytotoxic chemotherapy and external-beam radiation therapy, are limited and essentially ineffective for metastatic medullary thyroid carcinoma (MTC). In the last decade, small-molecule tyrosine kinase inhibitors (TKI) have been introduced in the field of thyroid cancer, after having been shown effective in a wide variety of other tumors. This review focuses on vandetanib (ZD6474, Zactima™; AstraZeneca) and its role in the treatment of MTC. Vandetanib is an oral TKI that targets VEGF receptors 2 and 3, RET, and at higher concentrations, the epidermal growth factor (EGF) receptor. This drug has been tested in two important phase II studies which demonstrated that both the 100 and 300 mg/day dosage of vandetanib have antitumor activity on advanced MTC. A phase III trial (ZETA trial) evaluating vandetanib in 331 patients with locally advanced or metastatic MTC showed a significant prolongation of PFS for patients receiving vandetanib compared with placebo. Toxicity surveillance in all studies reported high rates of adverse effects with diarrhea, rash, fatigue and nausea being the most commonly experienced by patients. Vandetanib is currently approved in the United States for unresectable locally advanced or metastatic MTC and has become a new standard of care in this rare and indolent pathology.

Positive selection for new disease mutations in the human germline: evidence from the heritable cancer syndrome multiple endocrine neoplasia type 2B

Multiple endocrine neoplasia type 2B (MEN2B) is a highly aggressive thyroid cancer syndrome. Since almost all sporadic cases are caused by the same nucleotide substitution in the RET proto-oncogene, the calculated disease incidence is 100-200 times greater than would be expected based on the genome average mutation frequency. In order to determine whether this increased incidence is due to an elevated mutation rate at this position (true mutation hot spot) or a selective advantage conferred on mutated spermatogonial stem cells, we studied the spatial distribution of the mutation in 14 human testes. In donors aged 36-68, mutations were clustered with small regions of each testis having mutation frequencies several orders of magnitude greater than the rest of the testis. In donors aged 19-23 mutations were almost non-existent, demonstrating that clusters in middle-aged donors grew during adulthood. Computational analysis showed that germline selection is the only plausible explanation. Testes of men aged 75-80 were heterogeneous with some like middle-aged and others like younger testes. Incorporating data on age-dependent death of spermatogonial stem cells explains the results from all age groups. Germline selection also explains MEN2B's male mutation bias and paternal age effect. Our discovery focuses attention on MEN2B as a model for understanding the genetic and biochemical basis of germline selection. Since RET function in mouse spermatogonial stem cells has been extensively studied, we are able to suggest that the MEN2B mutation provides a selective advantage by altering the PI3K/AKT and SFK signaling pathways. Mutations that are preferred in the germline but reduce the fitness of offspring increase the population's mutational load. Our approach is useful for studying other disease mutations with similar characteristics and could uncover additional germline selection pathways or identify true mutation hot spots.

A Case of Multiple Endocrine Neoplasia Type 2B and Gangliomatosis of Gastrointestinal Tract

Multiple endocrine neoplasia type 2 (MEN2) is a rare familial syndrome caused by mutations in the RET protooncogene and it is transmitted as an autosomal dominant trait. The underlying problem for all the MEN syndromes is failure of a tumour suppressor gene. The genetic defect in MEN2 is on chromosome 10 (10q11.2) and has also been identified both for MEN2A and MEN2B. The reported patient is an 18-year-old girl presented with long-term diarrhea and enterocutaneous fistula. Her thyroid nodules, marfanoid habitus and bumpy lips, were also highly suggestive for MEN2B.

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.

Molecular basis of medullary thyroid carcinoma: the role of RET polymorphisms

Medullary thyroid carcinoma is a rare malignant tumor originating in parafollicular C cells. It accounts for 5 to 8% of all thyroid cancers. MTC develops in either sporadic (75%) or hereditary form (25%). Genetic and molecular studies have demonstrated the involvement of the RET proto-oncogene in hereditary MTC and, less often, in its sporadic form. Although a strong genotype-phenotype correlation has been described, wide clinical heterogeneity is observed among families with the same RET mutation or even in carriers of the same kindred. In recent years, several single nucleotide polymorphisms of the RET gene have been described in the general population as well as in patients with MTC. Some studies have reported associations between the presence of polymorphisms and development or progression of MTC. Nonetheless, other studies failed to demonstrate any effect of the RET variants. Differences in the genetic background of distinct populations or methodological approaches have been suggested as potential reasons for the conflicting results. Here, we review current knowledge concerning the molecular pathogenesis of sporadic and hereditary MTC. In particular, we analyze the role of RET polymorphisms in the clinical presentation and prognosis of MTC based on the current literature.

Genetic interactions and modifier genes in Hirschsprung's disease

Hirschsprung’s disease is a congenital disorder that occurs in 1:5000 live births. It is characterised by an absence of enteric neurons along a variable region of the gastrointestinal tract. Hirschsprung’s disease is classified as a multigenic disorder, because the same phenotype is associated with mutations in multiple distinct genes. Furthermore, the genetics of Hirschsprung’s disease are highly complex and not strictly Mendelian. The phenotypic variability and incomplete penetrance observed in Hirschsprung’s disease also suggests the involvement of modifier genes. Here, we summarise the current knowledge of the genetics underlying Hirschsprung’s disease based on human and animal studies, focusing on the principal causative genes, their interactions, and the role of modifier genes.

Genetics and clinical characteristics of hereditary pheochromocytomas and paragangliomas

Pheochromocytomas (PCCs) and paragangliomas (PGLs) are rare neuroendocrine tumors of the adrenal glands and the sympathetic and parasympathetic paraganglia. They can occur sporadically or as a part of different hereditary tumor syndromes. About 30% of PCCs and PGLs are currently believed to be caused by germline mutations and several novel susceptibility genes have recently been discovered. The clinical presentation, including localization, malignant potential, and age of onset, varies depending on the genetic background of the tumors. By reviewing more than 1700 reported cases of hereditary PCC and PGL, a thorough summary of the genetics and clinical features of these tumors is given, both as part of the classical syndromes such as multiple endocrine neoplasia type 2 (MEN2), von Hippel-Lindau disease, neurofibromatosis type 1, and succinate dehydrogenase-related PCC-PGL and within syndromes associated with a smaller fraction of PCCs/PGLs, such as Carney triad, Carney-Stratakis syndrome, and MEN1. The review also covers the most recently discovered susceptibility genes including KIF1Bβ, EGLN1/PHD2, SDHAF2, TMEM127, SDHA, and MAX, as well as a comparison with the sporadic form. Further, the latest advances in elucidating the cellular pathways involved in PCC and PGL development are discussed in detail. Finally, an algorithm for genetic testing in patients with PCC and PGL is proposed.

Mouse models for inherited endocrine and metabolic disorders

In vivo models represent important resources for investigating the physiological mechanisms underlying endocrine and metabolic disorders, and for pre-clinical translational studies that may include the assessments of new treatments. In the study of endocrine diseases, which affect multiple organs, in vivo models provide specific advantages over in vitro models, which are limited to investigation of isolated systems. In recent years, the mouse has become the popular choice for developing such in vivo mammalian models, as it has a genome that shares ∼85% identity to that of man, and has many physiological systems that are similar to those in man. Moreover, methods have been developed to alter the expression of genes in the mouse, thereby generating models for human diseases, which may be due to loss- or gain-of-function mutations. The methods used to generate mutations in the mouse genome include: chemical mutagenesis; conventional, conditional and inducible knockout models; knockin models and transgenic models, and these strategies are often complementary. This review describes some of the different strategies that are utilised for generating mouse models. In addition, some mouse models that have been successfully generated by these methods for some human hereditary endocrine and metabolic disorders are reviewed. In particular, the mouse models generated for parathyroid disorders, which include: the multiple endocrine neoplasias; hyperparathyroidism-jaw tumour syndrome; disorders of the calcium-sensing receptor and forms of inherited hypoparathyroidism are discussed. The advances that have been made in our understanding of the mechanisms of these human diseases by investigations of these mouse models are described.

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.

High-resolution analysis of alterations in medullary thyroid carcinoma genomes

Hereditary and sporadic medullary thyroid carcinoma (MTC) are closely associated with RET proto-oncogene mutations. However, the role of additional changes in the tumor genomes remains unclear. Our objective was the identification of chromosomal regions involved in MTC tumorigenesis and to assess their significance by using MTC-derived cell lines. We used array-CGH (comparative genomic hybridization) to map chromosomal imbalances in 52 primary tumors and ten metastases. Eleven tumors (11/52, 21%) were hereditary and 41 (41/52, 79%) were sporadic. Among the latter, 15 tumors (15/41, 37%) harbored RET mutations. Furthermore, we characterized five MTC cell lines in detail and evaluated the tumorigenicity by severe combined immunodeficiency (SCID)-mouse experiments. Most MTCs had only few copy number changes, and losses of chromosomes 1p, 4q, 19p and 22q were observed most frequently. The number of chromosomal aberrations increased in metastases. Twenty-three percent (12/52) of the primary tumors did not even show any chromosomal gains and losses. We injected three cell lines (two of these were without chromosomal changes and pathogenic RET mutations) into immune deficient SCID mice, and in each case, we observed rapid tumor growth at the injection sites. Our data suggest that MTCs--in contrast to most other tumor entities--do not acquire a multitude of genomic imbalances. SCID mouse experiments performed with chromosomally normal cell lines and without RET mutations suggest that presently unknown submicroscopic genomic changes are sufficient in MTC tumorigenesis.

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.

In vitro transforming potential, intracellular signaling properties, and sensitivity to a kinase inhibitor (sorafenib) of RET proto-oncogene variants Glu511Lys, Ser649Leu, and Arg886Trp

Multiple endocrine neoplasia type 2 and a subset of apparently sporadic medullary thyroid carcinoma (AS-MTC) are caused by germ line activating point mutations of the rearranged during transfection (RET) proto-oncogene. RET encodes a receptor with tyrosine kinase activity that targets several intracellular signaling cascades, such as RAS-RAF-ERK1/2, PIK3-AKT, and STAT transcription factors. The objective of this study was to assess the function of three germ line RET variants Arg886Trp, Ser649Leu, and Glu511Lys of undetermined pathogenic significance, which were found in three kindreds of isolated AS-MTC. For this purpose, we employed vectors expressing each of the RET variants and measured the number of NIH3T3 transformation foci and soft agar colonies, the degree of activation of known RET intracellular signaling targets (ERK1/2, STAT1, STAT3, and TCF4), and the extent of ERK1/2 inhibition on sorafenib treatment. We found that RET variants Arg886Trp and Glu511Lys have shown increased in vitro transforming potential in a glial-derived neurotrophic factor-dependent manner. In contrast, the Ser649Leu variant did not significantly increased the number of foci and agar colonies relative to wild-type RET (RET-WT). The variants Glu511Lys and Arg886Trp showed 10- and 12.5-fold ERK1/2 activation respectively, that was significantly higher than that observed for RET-WT (fivefold). Increased levels of STAT1 and TCF4 activation were only observed for RET Arg886Trp (2.5- and 3-fold versus 1.2- and 2-fold in RET-WT respectively). The three RET variants analyzed here were sensitive to treatment with sorafenib. In conclusion, our results allow to classify previously uncharacterized RET genotypes, which may be of use to define follow-up and therapeutic regimens.

How to Treat a Signal? Current Basis for RET-Genotype-Oriented Choice of Kinase Inhibitors for the Treatment of Medullary Thyroid Cancer

The significance of RET in thyroid cancer comes from solid evidence that, when inherited, an RET activating mutation primes C-cells to transform into medullary carcinomas. Moreover, environmental exposure to radiation also induces rearranged transforming RET “isoforms” that are found in papillary thyroid cancer. The RET gene codes for a tyrosine kinase receptor that targets a diverse set of intracellular signaling pathways. The nature of RET point mutations predicts differences in the mechanisms by which the receptor becomes activated and correlates with different forms of clinical presentation, age of onset, and biological aggressiveness. A number of RET-targeting Tyrosine Kinase Inhibitors (TKIs) are currently undergoing clinical trials to evaluate their effectiveness in the treatment of thyroid cancer, and it is conceivable that the RET genotype may also influence response to these compounds. The question that now emerges is whether, in the future, the rational for treatment of refractory thyroid cancer will be based on the management of an abnormal RET signal. In this paper we address the RET-targeting TKIs and review studies about the signaling properties of distinct RET mutants as a means to predict response and design combinatorial therapies for the soon to be available TKIs.

Molecular analysis of the RET proto-oncogene key exons in patients with medullary thyroid carcinoma: a comprehensive study of the Iranian population

BACKGROUND

Germ-line mutations of RET proto-oncogene are the known cause of hereditary medullary thyroid carcinoma (MTC), which account for approximately 25% of all MTC cases and occur as multiple endocrine neoplasia type 2 syndromes. Here, we present the first comprehensive genetic screening and analysis of MTC among Iranian families.

METHODS

A total of 55 patients with MTC (male to female ratio=1:1.6; average age of disease onset = 33 ± 13 years) from 53 independent families participated in this study. All of the patients had undergone total thyroidectomy between 1999 and 2006, and 51 of them were clinically characterized as apparently sporadic cases. Genomic DNA samples were obtained and following highly-specific polymerase chain reaction amplification of the 6 RET key exons (10, 11, 13, 14, 15, and 16) were subjected to direct DNA sequencing without a requirement for a purification step.

RESULTS

Sequence analysis revealed that 9 (17.6%) of the apparently sporadic cases (from 8 kindreds) carried an RET germ-line mutation. Of the seven different mutations identified among all of the families studied, five were in the cysteine codons, with Cys634Arg having the highest prevalence (45.5%) among the afflicted families. Mutation carriers have an earlier age of onset (21 ± 6) versus the sporadic cases (37 ± 12).

CONCLUSIONS

This is the first comprehensive genetic screening and analysis of MTC among Iranian families. The results further confirm the need and advantages of DNA sequencing for identification of hereditary MTC cases. There does not seem to be a meaningful correlation between single nucleotide polymorphism patterns and the average age of disease onset. Geographical distribution of the sporadic cases, however, shows a significant concentration toward the Northern regions of the country, noticeably the provinces situated directly to the south of the Caspian Sea.

Familial thyroid cancer: a review

Thyroid carcinomas can be sporadic or familial. Familial syndromes are classified into familial medullary thyroid carcinoma (FMTC), derived from calcitonin-producing C cells, and familial non-medullary thyroid carcinoma, derived from follicular cells. The familial form of medullary thyroid carcinoma (MTC) is usually a component of multiple endocrine neoplasia (MEN) IIA or IIB, or presents as pure FMTC syndrome. The histopathological features of tumors in patients with MEN syndromes are similar to those of sporadic tumors, with the exception of bilaterality and multiplicity of tumors. The genetic events in the familial C-cell-derived tumors are well known, and genotype-phenotype correlations well established. In contrast, the case for a familial predisposition of non-medullary thyroid carcinoma is only now beginning to emerge. Although, the majority of papillary and follicular thyroid carcinomas are sporadic, the familial forms are rare and can be divided into two groups. The first includes familial syndromes characterized by a predominance of non-thyroidal tumors, such as familial adenomatous polyposis and PTEN-hamartoma tumor syndrome, within others. The second group includes familial syndromes characterized by predominance of papillary thyroid carcinoma (PTC), such as pure familial PTC (fPTC), fPTC associated with papillary renal cell carcinoma, and fPTC with multinodular goiter. Some characteristic morphologic findings should alert the pathologist of a possible familial cancer syndrome, which may lead to further molecular genetics evaluation.

Analysis of Somatic Mutations in Cancer: Molecular Mechanisms of Activation in the ErbB Family of Receptor Tyrosine Kinases

The ErbB/EGFR/HER family of kinases consists of four homologous receptor tyrosine kinases which are important regulatory elements in many cellular processes, including cell proliferation, differentiation, and migration. Somatic mutations in, or over-expression of, the ErbB family is found in many cancers and is correlated with a poor prognosis; particularly, clinically identified mutations found in non-small-cell lung cancer (NSCLC) of ErbB1 have been shown to increase its basal kinase activity and patients carrying these mutations respond remarkably to the small tyrosine kinase inhibitor gefitinib. Here, we analyze the potential effects of the currently catalogued clinically identified mutations in the ErbB family kinase domains on the molecular mechanisms of kinase activation. Recently, we identified conserved networks of hydrophilic and hydrophobic interactions characteristic to the active and inactive conformation, respectively. Here, we show that the clinically identified mutants influence the kinase activity in distinctive fashion by affecting the characteristic interaction networks.

Acidification of the Golgi apparatus is indispensable for maturation but not for cell surface delivery of Ret

We examined the effect of concanamycin A and bafilomycin A1, inhibitors of the vacuolar proton-ATPase, on maturation and expression of Ret, a tyrosine kinase receptor for glial cell line-derived neurotrophic factor. Ret appeared as 150- and 170-kDa bands on sodium dodecyl sulfate-polyacrylamide gel electrophoresis gels and both forms were sensitive to peptide-N-glycosidase F. Western and immunocytochemical analyses revealed that the 150-kDa immature form of Ret accumulated in the Golgi apparatus upon treatment with vacuolar proton-ATPase inhibitors, whereas, the 170-kDa mature form of Ret was dramatically decreased. The result suggests that glycosylation of Ret during the conversion from immature forms to mature forms is pH sensitive, and is likely initiated in the acidic trans-Golgi apparatus. In contrast, glycosylation of nascent receptors to become immature receptors appeared to be pH insensitive, and are likely to take place in the endoplasmic reticulum. The immature form of Ret was present in the plasma membrane when the cells were treated with the vacuolar proton-ATPase inhibitors. In conclusion, the acidification of the Golgi apparatus is crucial for maturation of Ret but not indispensable for trafficking of receptors to the membrane.

The crystal structure of a constitutively active mutant RON kinase suggests an intramolecular autophosphorylation hypothesis

A complex of RON(M1254T) with AMP-PNP and Mg(2+) reveals a substratelike positioning of Tyr1238 as well as likely catalysis-competent placement of the AMP-PNP and Mg(2+) components and indicates a tendency for cis phosphorylation. The structure shows how the oncogenic mutation may cause the constitutive activation and suggests a mechanistic hypothesis for the autophosphorylation of receptor tyrosine kinases.

Familial thyroid neoplasia: impact of technological advances on detection and monitoring

PURPOSE OF REVIEW

To weigh the clinical impact of new technological insights into heritable thyroid malignancies.

RECENT FINDINGS

Medullary thyroid carcinoma and familial nonmedullary thyroid cancers represent the small minority of thyroid cancers that are inherited. New insights into the genetic alterations and molecular mechanisms implicated in these tumors are serving to refine the clinical tools available for their initial diagnosis as well as subsequent follow-up. In addition to an analysis of rearranged during transfection mutations and calcitonin profiles in medullary thyroid carcinoma, this review includes emphasis on familial nonmedullary thyroid cancer syndromes, including genetic findings in familial papillary thyroid cancer, familial adenomatous polyposis, Cowden syndrome, Carney complex, and Werner syndrome.

SUMMARY

Genetic mutational information is increasingly available on medullary and familial nonmedullary thyroid cancer and their associated syndromes. The clinical significance of this information for affected patients and their families continues to undergo evaluation.

Mendelian genetics of rare--and not so rare--cancers

Mendelian genetics forms the basis for gene-informed risk assessment and management for the patient and family, and should be at the very foundation of 21st century personalization of healthcare. Yet this is an underutilized commodity. Identification and characterization of germline mutations in the RET proto-oncogene, encoding a receptor tyrosine kinase, as causing >90% of multiple endocrine neoplasia type 2 (MEN 2), an autosomal dominant disorder characterized by medullary thyroid cancer, pheochromocytoma, and hyperparathyroidism, heralded the era of evidence-based molecular diagnosis, predictive testing, genetic counseling, gene-informed cancer risk assessment, and preventative medicine. Since then, many syndromic endocrine neoplasias have proven to fall under this clinically utile and actionable model, such as those caused by mutations in RET, VHL, or SDHB-D. The familial risk associated with epithelial (nonmedullary) thyroid carcinoma is among the highest of all solid tumors, yet only a few highly penetrant heritable epithelial thyroid cancer syndrome exist. This is illustrated by Cowden syndrome, a difficult-to-recognize autosomal dominant disorder characterized by breast, thyroid, and other cancers, caused by germline mutations in PTEN, encoding a phosphatase, and minorly, SDHB/SDHD variants.

Medullary thyroid carcinoma

Medullary thyroid carcinoma (MTC) accounts for 5-8% of all thyroid cancers. MTC is mainly sporadic in nature, but an hereditary pattern [multiple endocrine neoplasia type 2 (MEN 2)] is present in 20-30% of cases, transmitted as an autosomal-dominant trait due to germline mutations of the RET proto-oncogene. About 98% of patients with MEN 2 have germline mutations in exons 5, 8, 10, 11, 13, 14, 15 or 16 of the RET gene. The primary treatment of both hereditary and sporadic forms of MTC is total thyroidectomy and removal of all neoplastic tissue present in the neck. The therapeutic option for lymph node surgery should be dictated by the results of presurgical evaluation. After total thyroidectomy, measurements of serum calcitonin (CT) and carcinoembryonic antigen are of paramount importance in the postsurgical follow-up of patients with MTC as they reflect the presence of persistent or recurrent disease. Complete remission is demonstrated by undetectable and stimulated serum CT measurement. On the contrary, if serum CT is detectable under basal conditions or becomes detectable after stimulation, the patient is probably not cured, but imaging techniques will not demonstrate any disease until serum CT approaches levels >150 pg/ml. The tumour metastasises early to both paratracheal and lateral cervical lymph nodes. Metastases outside the neck may occur in the liver, lungs, bones and, less frequently, brain and skin. Surgery is the main treatment for local and distant metastases whenever feasible. Systemic chemotherapy with dacarbazine, 5-fluorouracil and doxorubicin (alone or in combination) has shown very limited efficacy, achieving only partial responses in the range of 10-20% and of short duration. Several kinase inhibitors are currently under evaluation and preliminary results are promising. Familial cases must be identified by searching for RET proto-oncogene mutations in the proband and in family members. Carriers of the RET gene are candidates for prophylactic thyroidectomy at different ages depending on the risk associated with the specific RET mutations.

Multiple endocrine neoplasia type 2

Multiple endocrine neoplasia type 2 (MEN 2) is an autosomal dominant cancer syndrome with major components of medullary thyroid carcinoma (MTC), pheochromocytoma and hyperparathyroidism. The disease is caused by germline mutations of the RET proto-oncogene. Subtypes of MEN 2 include MEN 2A, MEN 2B and familial MTC (FMTC) which differ in pattern of additional lesions or--in FMTC--lack of pheochromocytoma. In 2009, after extensive review of the literature, the guidelines of the American Thyroid Association made several recommendations regarding clinical and genetic diagnostic testing and treatment options. In this article, the recently published literature is reviewed and concerns regarding future perspectives are added. In particular, a critical handling of rare DNA variants and double mutations is necessary. Up to now, mutation-specific risk profiles and mutation-associated treatment recommendations are unavailable. We emphasise the need for approved centres for treatment of patients affected by MEN 2, not only adults but young children as well. As a high level of skill is required for endoscopic adrenal-sparing surgery, surgeons should declare their expertise before operating such patients. Registry-based follow-up should be mandatory including documentation of short- and long-term outcome in order to provide valid data for future counselling of patients with MEN 2.

Analysis of DOK-6 function in downstream signaling of RET in human neuroblastoma cells

Point mutations and structural alterations of the RET tyrosine kinase gene cause multiple endocrine neoplasia type 2 (MEN 2) and papillary thyroid carcinoma, respectively. RET activation by glial cell line-derived neurotrophic factor (GDNF) is essential for the development of the enteric nervous system and the kidney. The signal through RET tyrosine kinase requires several adaptor proteins including the DOK (downstream of kinase) family of proteins. Of the seven members of the DOK protein family, DOK-1, -4, -5, and -6 have been reported to play roles in the GDNF-RET signaling pathway. Although DOK-6 has been shown to bind to RET and promote GDNF-induced neurite outgrowth in mouse Neuro2A cells, DOK-6 function in human cells remains unclear. In the present study, we investigated the role of DOK-6 in GDNF-RET signaling in human cells including neuroblastoma cells. DOK-6 was constitutively localized to the plasma membrane via its pleckstrin homology (PH) domain, and was phosphorylated following RET activation via a MEN2A mutation or GDNF stimulation. However, DOK-6 could not significantly affect downstream signaling and neurite outgrowth in human neuroblastoma cells. The binding affinity of the DOK-6 phosphotyrosine-binding (PTB) domain to RET was much lower than that of the DOK-1, DOK-4, and SHC PTB domains to RET. These findings indicate that DOK-6 is involved in RET signaling with less influence when compared with DOK-1, DOK-4, and SHC.

Reports of clinical benefit of plitidepsin (Aplidine), a new marine-derived anticancer agent, in patients with advanced medullary thyroid carcinoma

OBJECTIVES

To assess clinical benefit of plitidepsin (Aplidine) in patients with advanced medullary thyroid carcinoma (MTC).

MATERIALS AND METHODS

We retrospectively reported the outcome of 10 patients with advanced MTC among 215 patients who have entered the phase I program with plitidepsin.

RESULTS

Median number of cycles was 5. Using World Health Organization criteria, 1 among 5 patients with measurable disease displayed a confirmed partial response, whereas 8 patients experienced a stable disease, and 1 patient had a progressive disease, corresponding to a disease control rate of 90%. Two patients treated at the maximum tolerated dose experienced muscular dose-limiting toxicity possibly related to palmitoyl transferase inhibition. One of these 2 patients was able to continue therapy with no dose reduction with the prophylactic addition of l-carnitine, which is used in the treatment of the carnitine palmitoyl transferase deficiency type 2.

DISCUSSION

Plitidepsin seems to be able to induce clinical benefit in patients with pretreated MTC, and its toxicity has been manageable at the recommended dose.

Inhibitors of the RET tyrosine kinase based on a 2-(alkylsulfanyl)-4-(3-thienyl)nicotinonitrile scaffold

In an approach to optimize 2-(4-fluorobenzylsulfanyl)-4-(2-thienyl)-5,6,7,8-tetrahydroquinoline-3-carbonitrile (1a), a weak inhibitor of the cancer-related tyrosine kinase RET originating from a screening campaign, analogues with 3-thienyl substitution were prepared. Among the novel derivatives, 2-amino-6-{[2-(4-chlorophenyl)-2-oxoethyl]sulfanyl}-4-(3-thienyl)pyridine-3,5-dicarbonitrile (13 g) was identified as a submicromolar RET inhibitor, displaying 3- and 100-fold selectivity versus ALK and ABL kinases, respectively. The novel inhibitor exhibited antiproliferative activity in the micromolar concentration range against both RET-dependent and RET-independent cancer cell lines. Docking experiments suggest a binding mode of the new inhibitors in the ATP binding pocket of the target kinase, explaining the observed structure-activity relationships.

Selection criteria for c-Met-targeted therapies: emerging evidence for biomarkers

Extensive development of targeted therapies emphasize the critical need for biomarkers and major efforts have been engaged to identify screening, prognostic, stratification and therapy-monitoring markers. One of the challenges in translating preclinical studies into effective clinical therapies remains the accurate identification of a responsive subsets of patients. Studies on trastuzumab demonstrated that patient response could be specifically correlated with the amplification of the Her2 gene. However, for the EGF receptor, it has been more difficult to find the right stratification biomarker and recent data demonstrate that genetic alterations for the EGF receptor have to be considered. Taken together, these data underline the need for a deeper understanding of both targeted receptor and human disease to determine pathways that might be investigated during early clinical trials in order to define relevant biomarkers for patient selection. This article, dealing with the c-Met tyrosine kinase receptor, provides an overview of c-Met alterations observed in cancer and proposes approaches for stratification biomarker selection.

Vandetanib for the treatment of patients with locally advanced or metastatic hereditary medullary thyroid cancer

PURPOSE There is no effective therapy for patients with distant metastasis of medullary thyroid carcinoma (MTC). Activating mutations in the RET proto-oncogene cause hereditary MTC, which provides a strong therapeutic rationale for targeting RET kinase activity. This open-label, phase II study assessed the efficacy of vandetanib, a selective oral inhibitor of RET, vascular endothelial growth factor receptor, and epidermal growth factor receptor signaling, in patients with advanced hereditary MTC. METHODS Patients with unresectable locally advanced or metastatic hereditary MTC received initial treatment with once-daily oral vandetanib 300 mg. The dose was adjusted additionally in some patients on the basis of observed toxicity until disease progression or any other withdrawal criterion was met. The primary assessment was objective tumor response (by RECIST [Response Evaluation Criteria in Solid Tumors]). Results Thirty patients received initial treatment with vandetanib 300 mg/d. On the basis of investigator assessments, 20% of patients (ie, six of 30 patients) experienced a confirmed partial response (median duration of response at data cutoff, 10.2 months). An additional 53% of patients (ie, 16 of 30 patients) experienced stable disease at >/= 24 weeks, which yielded a disease control rate of 73% (ie, 22 of 30 patients). In 24 patients, serum calcitonin levels showed a 50% or greater decrease from baseline that was maintained for at least 4 weeks; 16 patients showed a similar reduction in serum carcinoembryonic antigen levels. The most common adverse events were diarrhea (70%), rash (67%), fatigue (63%), and nausea (63%). CONCLUSION In this study, vandetanib demonstrated durable objective partial responses and disease control with a manageable adverse event profile. These results demonstrate that vandetanib may provide an effective therapeutic option in patients with advanced hereditary MTC, a rare disease for which there has been no effective therapy.

Activation of the N-terminally truncated form of the Stk receptor tyrosine kinase Sf-Stk by Friend virus-encoded gp55 is mediated by cysteine residues in the ecotropic domain of gp55 and the extracellular domain of Sf-Stk

Friend virus induces an erythroleukemia in susceptible mice that is initiated by the interaction of the Friend virus-encoded glycoprotein gp55 with the erythropoietin (Epo) receptor and the product of the host Fv2 gene, a naturally occurring truncated form of the Stk receptor tyrosine kinase (Sf-Stk). We have previously demonstrated that the activation of Sf-Stk, recruitment of a Grb2/Gab2/Stat3 signaling complex, and induction of Pu.1 expression by Stat3 are required for the development of the early stage of Friend disease both in vitro and in vivo. Here we demonstrate that the interaction of gp55 with Sf-Stk is dependent on cysteine residues in the ecotropic domain of gp55 and the extracellular domain of Sf-Stk. Point mutation of these cysteine residues or deletion of these domains inhibits the ability of gp55 to interact with Sf-Stk, resulting in the inability of these proteins to promote the Epo-independent growth of erythroid progenitor cells. We also demonstrate that the interaction of gp55 with Sf-Stk does not promote dimerization of Sf-Stk but results in enhanced phosphorylation of Sf-Stk and the relocalization of Sf-Stk from the cytosol to the plasma membrane. Finally, we demonstrate that a constitutively active form of Sf-Stk (Sf-StkM330T), as well as its human counterpart, Sf-Ron, promotes Epo-independent colony formation in the absence of gp55 and that this response is also dependent on the cysteines in the extracellular domains of Sf-StkM330T and Sf-Ron. These data suggest that the cysteines in the extracellular domains of Sf-Stk and Sf-Ron may also mediate the interaction of these truncated receptors with other cellular factors that regulate their ability to promote cytokine-independent growth.