Molecular pathogenesis of MEN2-associated tumors

Retroposed copies of RET gene: a somatically acquired event in medullary thyroid carcinoma

BACKGROUND

Different pathogenic germline mutations in the RET oncogene are identified in MEN 2, a hereditary syndrome characterized by medullary thyroid carcinoma (MTC) and other endocrine tumors. Although genetic predisposition is recognized, not all RET mutation carriers will develop the disease during their lifetime or, likewise, RET mutation carriers belonging to the same family may present clinical heterogeneity. It has been suggested that a single germline mutation might not be sufficient for development of MEN 2-associated tumors and a somatic bi-allelic alteration might be required. Here we investigated the presence of somatic second hit mutation in the RET gene in MTC.

METHODS

We integrated Multiplex Ligation-dependent Probe Amplification (MLPA) and whole exome sequencing (WES) to search for copy number alteration (CNA) in the RET gene in MTC samples and medullary thyroid cell lines (TT and MZ-CR-1). We next found reads spanning exon-exon boundaries on RET, an indicative of retrocopy. We subsequently searched for RET retrocopies in the human reference genome (GRCh37) and in the 1000 Genomes Project data, by looking for reads reporting joined exons in the RET locus or distinct genomic regions. To determine RET retrocopy specificity and recurrence, DNA isolated from sporadic and MEN 2-associated MTC (n = 37), peripheral blood (n = 3) and papillary thyroid carcinomas with RET fusion (n = 10) samples were tested using PCR-sequencing methodology.

RESULTS

Through MLPA we have found evidence of CNA in the RET gene in MTC samples and MTC cell lines. WES analysis reinforced the presence of the CNA and hinted for a retroposed copy of RET not found in the human reference genome and 1.000 Genomes Project. Extended analysis confirmed the presence of a somatic MTC-related retrocopy of RET in both sporadic and hereditary tumors. We further unveiled a recurrent (28%) novel point mutation (p.G548 V) found exclusively in the retrocopy of RET. The mutation was also found in cDNA of mutated samples, suggesting it might be functional.

CONCLUSION

We here report a somatic specific RET retroposed copy in MTC samples and cell lines. Our results support the idea that generation of retrocopies in somatic cells is likely to contribute to MTC genesis and progression.

Multilayered heterogeneity as an intrinsic hallmark of neuroendocrine tumors

Neuroendocrine tumors (NETs) comprise a complex and highly heterogeneous group of neoplasms that can arise all over the body, originating from neuroendocrine cells. NETs are characterized by a general lack of symptoms until they are in advanced phase, and early biomarkers are not as available and useful as required. Heterogeneity is an intrinsic, pivotal feature of NETs that derives from diverse causes and ultimately shapes tumor fate. The different layers that conform NET heterogeneity include a wide range of distinct characteristics, from the mere location of the tumor to its clinical and functional features, and from its cellular properties, to the core signaling and (epi)genetic components defining the molecular signature of the tumor. The importance of this heterogeneity resides in that it translates into a high variability among tumors and, hence, patients, which hinders a more precise diagnosis and prognosis and more efficacious treatment of these diseases. In this review, we highlight the significance of this heterogeneity as an intrinsic hallmark of NETs, its repercussion on clinical approaches and tumor management, and some of the possible factors associated to such heterogeneity, including epigenetic and genetic elements, post-transcriptional regulation, or splicing alterations. Notwithstanding, heterogeneity can also represent a valuable and actionable feature, towards improving medical approaches based on personalized medicine. We conclude that NETs can no longer be viewed as a single disease entity and that their diagnosis, prognosis and treatment must reflect and incorporate this heterogeneity.

Hereditary syndromes predisposing to endocrine tumors and their skin manifestations

We often think of the lentiginoses, phacomatoses and other neurocutaneous syndromes as conditions that affect the skin and also predispose to a variety of tumors. However, we rarely think of Peutz-Jeghers syndrome (PJS), Carney complex (CNC), Cowden disease (CD), neurofibromatosis type-1 (NF-1) or tuberous sclerosis (TSC) as conditions that are multiple endocrine neoplasias (MEN). Indeed, all of these conditions predispose to a variety of endocrine tumors, in addition to many other neoplasms. On the other hand, the classic MENs, type 1 and 2 (MEN-1 and MEN-2, respectively) are almost never thought in terms of their skin manifestations. In this review, we present extensively the MEN-1, MEN-2 and PJS syndromes, and briefly refer to CD, NF-1, and TSC. CNC is discussed in another article in this journal issue.

Flushing in (neuro)endocrinology

Cutaneous flushing is a common presenting complaint in endocrine disorders. The pathophysiology of flushing involves changes in cutaneous blood flow triggered by multiple intrinsic factors that are either related to physiology or disease. Flushing can be divided into episodic or persistent causes. Episodic flushing is mediated by the release of endogenous vasoactive mediators or medications, while persistent flushing results in a fixed facial erythema with telangiectasia and cyanosis due to slow-flowing deoxygenated blood in large cutaneous blood vessels. The differential diagnosis of cutaneous flushing in neuroendocrine disorders is limited, yet encompasses a broad spectrum of benign and malignant entities, including carcinoid syndrome, pheochromocytoma, Cushing syndrome, medullary thyroid cancer, and pancreatic neuroendocrine tumors. In this review, we provide a concise and up-to-date discussion on the differential diagnosis and approach of flushing in neuroendocrinology.

Molecular pathways associated with aggressiveness of papillary thyroid cancer

The most common thyroid malignancy is papillary thyroid cancer (PTC). Mortality rates from PTC mainly depend on its aggressiveness. Geno- and phenotyping of aggressive PTC has advanced our understanding of treatment failures and of potential future therapies. Unraveling molecular signaling pathways of PTC including its aggressive forms will hopefully pave the road to reduce mortality but also morbidity from this cancer. The mitogen-activated protein kinase and the phosphatidylinositol 3-kinase signaling pathway as well as the family of RAS oncogenes and BRAF as a member of the RAF protein family and the aberrant expression of microRNAs miR-221, miR-222, and miR-146b all play major roles in tumor initiation and progression of aggressive PTC. Small molecule tyrosine kinase inhibitors targeting BRAF-mediated events, vascular endothelial growth factor receptors, RET/PTC rearrangements, and other molecular targets, show promising results to improve treatment of radioiodine resistant, recurrent, and aggressive PTC.

Multiple endocrine neoplasia syndromes associated with mutation of p27

Multiple endocrine neoplasias (MEN) are autosomal dominant disorders characterized by the occurrence of tumors in at least two endocrine glands. Until recently, two MEN syndromes were known, i.e. the MEN type 1 (MEN1) and type 2 (MEN2), which are caused by germline mutations in the MEN1 and RET genes, respectively. These two syndromes are characterized by a different tumor spectrum. A few years ago we described a variant of the MEN syndromes, which spontaneously developed in a rat colony and was named MENX. Affected animals consistently develop multiple endocrine tumors, with a spectrum that shares features with both MEN1 and MEN2 human syndromes. Genetic studies identified a germline mutation in the Cdkn1b gene, encoding the p27 cell cycle inhibitor, as the causative mutation for MENX. Capitalizing on these findings, germline mutations in the human homologue, CDKN1B, were searched for and identified in patients with multiple endocrine tumors. As a consequence of this discovery, a novel human MEN syndrome, named MEN4, was recognized, which is caused by heterozygous mutations in p27. These studies identified Cdkn1b/CDKN1B as a novel tumor susceptibility gene for multiple endocrine tumors in both rats and humans. Here we review the characteristics of the MENX and MEN4 syndromes and we briefly address the main function of p27 and how it is affected by MENX- or MEN4-associated mutations.

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.

p27kip1: a new multiple endocrine neoplasia gene?

Multiple endocrine neoplasias (MEN) are autosomal dominant disorders characterized by the occurrence of tumors in at least two endocrine glands. Two types of MEN syndromes have long been known: MEN type 1 (MEN1) and MEN type 2 (MEN2), associated with a different spectrum of affected organs. MEN1 and MEN2 are caused by germline mutations in the MEN1 tumor suppressor gene and the RET proto-oncogene, respectively. Lately, a new type of MEN was identified (named MEN4) which is due to mutations in the CDKN1B gene, encoding for p27kip1 (p27), a cyclin-dependent kinase (Cdk) inhibitor that regulates the transition of cells from G1 to S phase. p27 is a non-canonical tumor suppressor since it is usually not somatically mutated in human cancers but it is often downregulated by post-translational mechanisms. The discovery of MEN4 has defined a new role for CDKN1B as a tumor susceptibility gene for multiple endocrine tumors. To date, six germline CDKN1B mutations have been found in patients with a MEN1-like phenotype but negative for MEN1 mutations. Due to the limited number of patients so far identified, the phenotypic features of MEN4 are not clearly defined. Here, we review the clinical and molecular characteristics of the MEN4 syndrome and summarize the main functions of p27 to better comprehend how their alteration can predispose to neuroendocrine tumors.

Clustering of sebaceous gland carcinoma, papillary thyroid carcinoma and breast cancer in a woman as a new cancer susceptibility disorder: a case report

Introduction

Multiple distinct tumors arising in a single individual or within members of a family raise the suspicion of a genetic susceptibility disorder.

Case presentation

We present the case of a 52-year-old Caucasian woman diagnosed with sebaceous gland carcinoma of the eyelid, followed several years later with subsequent diagnoses of breast cancer and papillary carcinoma of the thyroid. Although the patient was also exposed to radiation from a pipe used in the oil field industry, the constellation of neoplasms in this patient suggests the manifestation of a known hereditary susceptibility cancer syndrome. However, testing for the most likely candidates such as Muir-Torre and Cowden syndrome proved negative.

Conclusion

We propose that our patient's clustering of neoplasms either represents a novel cancer susceptibility disorder, of which sebaceous gland carcinoma is a characteristic feature, or is a variant of the Muir-Torre syndrome.

Mosaicism in von Hippel-Lindau disease: an event important to recognize

von Hippel-Lindau disease (VHL) is an autosomal dominant, familial neoplastic disorder with variable interfamilial and intrafamilial expression. VHL is characterized by pre-disposition to development of a combination of benign and malignant tumours affecting multiple organs. We provide molecular evidence of somatic mosaicism in nearly asymptomatic man whose daughter had VHL. The mosaic subject was found to have a cyst of the kidney and an angioma of the glans penis and had had surgery for a mandibular cyst and epididymal cystadenomas. Mosaicism could provide a genetic explanation for the clinical heterogeneity and variable severity of VHL. The real incidence of mosaicism is still unclear and the identification of mosaicism has important consequences in genetic counseling of VHL patients who appear to have de novo VHL mutations and should be considered when evaluating patients with isolated VHL-related tumours. Our results strongly suggest a complete and extensive clinical examination in the parents of each patient affected by an apparently de novo VHL germline mutation. We recommend performing a mutation screening of both parents of a proband with techniques that permit detection of low percentages of mosaicism before concluding that the proband has a de novo VHL mutation.

Germline CDKN1B/p27Kip1 mutation in multiple endocrine neoplasia

CONTEXT

Germline mutations in the MEN1 gene predispose to multiple endocrine neoplasia type 1 (MEN1) syndrome, but in up to 20-25% of clinical MEN1 cases, no MEN1 mutations can be found. Recently, a germline mutation in the CDKN1B gene, encoding p27(Kip1), was reported in one suspected MEN1 family with two acromegalic patients.

OBJECTIVE

Our objective was to evaluate the role of CDKN1B/p27(Kip1) in human tumor predisposition in patients clinically suspected of MEN1 but testing negative for MEN1 germline mutation as well as in familial and sporadic acromegaly/pituitary adenoma patients.

DESIGN

Genomic DNA was analyzed for germline mutations in the CDKN1B/p27(Kip1) gene by PCR amplification and direct sequencing.

SETTING

The study was conducted at nonprofit academic research and medical centers.

PATIENTS

Thirty-six Dutch and one German suspected MEN1 patient, who previously tested negative for germline MEN1 gene mutations, were analyzed. In addition, 19 familial and 50 sporadic acromegaly/pituitary adenoma patients from Europe and the United States were included in the study.

MAIN OUTCOME MEASURES

We analyzed germline CDKN1B/p27(Kip1) mutations in individuals with pituitary adenoma and MEN1-like features.

RESULTS

A heterozygous 19-bp duplication (c.59_77dup19) leading to a truncated protein product was identified in one Dutch patient with suspected MEN1 phenotype, pituitary adenoma, carcinoid tumor, and hyperparathyroidism (one of 36, 2.8%). No mutations were detected in either familial or sporadic acromegaly/pituitary adenoma patients.

CONCLUSIONS

Our results support the previous finding that germline CDKN1B/p27(Kip1) mutations predispose to a human MEN1-like condition. However, such mutations appear uncommon in suspected MEN1 cases and rare or nonexistent in familial or sporadic acromegaly/pituitary adenoma patients.

Dermatologic aspects of thyroid disease

Thyroid disorders commonly have dermatologic manifestations. The purpose of the present chapter is to review and emphasize potential clinical dermatologic findings that can occur with Graves' disease, hypothyroidism and thyroid cancer. In autoimmune diseases such as Graves' disease and Hashimoto's thyroiditis the skin manifestations may be related to either thyroid hormone levels themselves or to the associated T and/or B cell abnormalities. Thyroid cancer may be associated with various syndromes that could have significant skin manifestations.

Comprehensive mutation scanning of NF1 in apparently sporadic cases of pheochromocytoma

BACKGROUND

Pheochromocytoma is a rare manifestation in patients with neurofibromatosis type 1 (NF 1). The 57-exon susceptibility gene NF1 has so far not been systematically scanned for unexpected germline mutations in individuals with sporadic pheochromocytoma.

METHODS

Twenty-seven patients with bilateral adrenal and/or extraadrenal abdominal pheochromocytoma not carrying germline mutations of the genes VHL, RET, SDHB, and SDHD were selected from the European-American pheochromocytoma registry. All 57 exons and flanking intronic regions of the NF1 gene were PCR amplified using newly designed primer pairs to exclude the amplification of pseudogenes. Intragenic mutation scanning was performed using denaturing HPLC and bidirectional direct sequencing.

RESULTS

Of the 27 apparently sporadic cases, one (4%) was found to have a pathogenic germline NF1 mutation, Leu303Arg. Clinical reevaluation of this individual, who had bilateral pheochromocytoma, revealed classic, but very mild, features of NF 1, one cutaneous neurofibroma, axillary freckling, and Lisch nodules of the iris as well as a few café-au-lait spots.

CONCLUSIONS

In the absence of germline mutations in VHL, RET, SDHD, and SDHB, patients with pheochromocytoma, especially with bilateral disease, should be checked thoroughly for clinical lesions suggestive of underlying syndromes such as the cutaneous and ophthalmological features characteristic of NF 1.

Somatic VHL gene alterations in MEN2-associated medullary thyroid carcinoma

Background

Germline mutations in RET are responsible for multiple endocrine neoplasia type 2 (MEN2), an autosomal dominantly inherited cancer syndrome that is characterized by medullary thyroid carcinoma (MTC), pheochromocytoma, and parathyroid hyperplasia/adenoma. Recent studies suggest a "second hit" mechanism resulting in amplification of mutant RET. Somatic VHL gene alterations are implicated in the pathogenesis of MEN2 pheochromocytomas. We hypothesized that somatic VHL gene alterations are also important in the pathogenesis of MEN2-associated MTC.

Methods

We analyzed 6 MTCs and 1 C-cell hyperplasia (CCH) specimen from 7 patients with MEN2A and RET germline mutations in codons 609, 618, 620, or 634, using microdissection, microsatellite analysis, phosphorimage densitometry, and VHL mutation analysis.

Results

First, we searched for allelic imbalance between mutant and wild-type RET by using the polymorphic markers D10S677, D10S1239, and RET on thyroid tissue from these patients. Evidence for RET amplification by this technique could be demonstrated in 3 of 6 MTCs. We then performed LOH analysis using D3S1038 and D3S1110 which map to the VHL gene locus at 3p25/26. VHL gene deletion was present in 3 MTCs. These 3 MTCs also had an allelic imbalance between mutant and wild-type RET. Mutation analysis of the VHL gene showed a somatic frameshift mutation in 1 MTC that also demonstrated LOH at 3p25/26. In the 2 other MTCs with allelic imbalance of RET and somatic VHL gene deletion, no somatic VHL mutation could be detected. The CCH specimen did neither reveal RET imbalance nor somatic VHL gene alterations.

Conclusion

These data suggest that a RET germline mutation is necessary for development of CCH, that allelic imbalance between mutant and wild-type RET may set off tumorigenesis, and that somatic VHL gene alterations may not play a major role in tumorigenesis of MEN2A-associated MTC.