High-resolution analysis of alterations in medullary thyroid carcinoma genomes

Comprehensive Assessment of Copy Number Alterations Uncovers Recurrent AIFM3 and DLK1 Copy Gain in Medullary Thyroid Carcinoma

Simple Summary

Medullary thyroid cancer (MTC) is often discovered in its advanced stage. Although a rare disease, advanced MTC cases have poor prognosis and the treatment is often palliative. Several studies have reported the existence of an association between copy number alterations (CNAs) burden and cancer progression. Moreover, the accumulation of broad CNAs, which contribute to intra-tumor heterogeneity, might be required for immune evasion. The identification of the recurrent CNAs associated with tumor phenotype aided in discovering new therapeutics options in several cancer types. To our knowledge, CNA is not well characterized in MTC. We analyzed recurrent focal CNAs on MTC. Our analysis provides a novel insight on MTC biology and may help in uncovering novel potential therapeutic targets.

Abstract

Medullary thyroid carcinoma (MTC) is a malignant tumor originating from thyroid C-cells that can occur either in sporadic (70–80%) or hereditary (20–30%) form. In this study we aimed to identify recurrent copy number alterations (CNA) that might be related to the pathogenesis or progression of MTC. We used Affymetrix SNP array 6.0 on MTC and paired-blood samples to identify CNA using PennCNV and Genotyping Console software. The algorithms identified recurrent copy number gains in chromosomes 15q, 10q, 14q and 22q in MTC, whereas 4q cumulated losses. Coding genes were identified within CNA regions. The quantitative PCR analysis performed in an independent series of MTCs (n = 51) confirmed focal recurrent copy number gains encompassing the DLK1 (14q32.2) and AIFM3 (22q11.21) genes. Immunohistochemistry confirmed AIFM3 and DLK1 expression in MTC cases, while no expression was found in normal thyroid tissues and few MTC samples were found with normal copy numbers. The functional relevance of CNA was also assessed by in silico analysis. CNA status correlated with protein expression (DLK1, p = 0.01), tumor size (DLK1, p = 0.04) and AJCC staging (AIFM3p = 0.01 and DLK1p = 0.05). These data provide a novel insight into MTC biology, and suggest a common CNA landscape, regardless of if it is sporadic or hereditary MTC.

Genomic and Transcriptomic Characterization of Sporadic Medullary Thyroid Carcinoma

Background: Sporadic medullary thyroid carcinoma (MTC) is a relatively uncommon neuroendocrine malignancy and the molecular tumorigenesis of its sporadic type (sMTC) is only partially understood. In this study, we performed a study focusing on the genomic and transcriptomic characterization of sMTC. Methods: Twenty-nine sMTC patients were included. Whole-exome sequencing (WES) was carried out in 18 patients, including both tumor samples and matched noncancerous tissues. Whole transcriptome sequencing (RNA-Seq) was performed in all 29 tumors. WES, RNA-Seq, and copy number alteration (CNA) data were analyzed. A Cell Counting Kit-8 (CCK-8) assay was used to evaluate cell proliferation. Results: Among the somatic mutations, RET was the only recurrently cancer-related mutated gene (5/18, 27.8%). In the germline, FAT1 and FAT4, two members of the FAT gene family, were identified as the two most common mutated genes. CNA analysis found that FAT1 and FAT4, both located on chromosome 4q, were also two of the genes most commonly affected by somatic chromosomal deletions (4/18, 22.2%). Using TT and MZ-CRC-1 cell lines, the CCK-8 assay showed that FAT1 and FAT4 knockdown could promote MTC cell proliferation. Based on the gene expression profile, patients were clustered into two molecular subtypes: the mesenchymal-like subtype is characterized by epithelial-mesenchymal transition, while the proliferative-like subtype is associated with enrichment of cell cycle pathways. Most events of structural recurrence (80%) occurred in the proliferative-like subtype. Conclusion: In addition to RET, these findings demonstrate that FAT1/FAT4 genomic alterations appear to be frequent in sMTC. Two molecular subtypes of sMTC with distinct biological behavior could be identified. However, these results need to be validated by larger samples and more comprehensive experiments in the future, especially for the frequency and function of FAT1/FAT4 germline variants.

The avian chorioallantoic membrane as an alternative tool to study medullary thyroid cancer

Preclinical trials of medullary thyroid cancer (MTC) therapeutics require both in vitro and in vivo analyses. Human tumour xenografted rodent models, which are considered the 'gold standard' to study and validate the efficacy and toxicity of lead compounds before translation to clinical trials, are very expensive, subject to organismal variability and ethical controversies. The avian chorioallantoic membrane (CAM) assay provides an alternative versatile, cost-effective and ethically less objectionable short-term, in vivo model for reliable screening of drugs. In this work, we grafted two MTC cell lines and patient-derived MTC tumour samples onto the avian CAM and characterised the resulted tumours histologically and immunohistochemically. Our findings provide the evidence that the CAM assay is a suitable model for studying the pathophysiology of MTC and can even be used as in vivo system for drug testing.

Calcium-stimulated calcitonin - The "new standard" in the diagnosis of thyroid C-cell disease - clinically relevant gender-specific cut-off levels for an "old test"

Introduction

Pentagastrin (Pg) stimulated calcitonin (sCT) was used to enhance accuracy in medullary thyroid cancer (MTC) diagnosis. As it is now unavailable, calcium (Ca) has been recommended as an alternative. The aim of this study was to define gender-specific cut-off values to predict MTC in patients with elevated basal CT (bCT) following Pg-sCT and Ca-sCT stimulation and to compare the time courses of CT release during stimulation.

Materials and methods

The stimulation tests were applied in 62 consecutive patients with thyroid nodules. Basal calcitonin was measured by chemiluminescent immunometric assay. All patients underwent thyroidectomy and bilateral central neck dissection. C-cell pathology was confirmed by histological and immunohistochemical evaluation.

Results

In 39 (0.63) patients MTC was documented while isolated C-cell hyperplasia (CCH) was identified in 23 (0.37) patients. Medullary thyroid cancer was predicted in males with bCT values > 43 pg/mL or sCT concentrations > 470 pg/mL (Pg-sCT) or > 1500 pg/mL (Ca-sCT), and in females with bCT concentrations > 23 pg/mL or sCT concentrations > 200 pg/mL (Pg-sCT) or > 780 pg/mL (Ca-sCT), respectively. Pg-sCT correctly predicted MTC in 16 (0.66) compared to 13 (0.54) after Ca-sCT in males and in 12 (0.80) compared to 11 (0.73) in females; without statistical significance. In patients with CCH or low tumor burden, there was a tendency of faster CT release after Ca stimulation (CT peak after 3min in > 60%) compared to patients with advanced MTC (CT peak after 3min in < 10%).

Conclusions

Using gender-specific cut-off values, Ca could replace Pg to predict MTC with similar diagnostic power.

Reduced Retinoblastoma Protein Expression Is Associated with Decreased Patient Survival in Medullary Thyroid Cancer

BACKGROUND

The retinoblastoma (RB) transcriptional corepressor 1 protein functions to slow cell-cycle progression. Inactivation of RB by reduced expression and/or hyperphosphorylation allow for enhanced progression through the cell cycle. Murine models develop medullary thyroid carcinoma (MTC) after generalized loss of RB. However, RB expression in MTC has only been evaluated in a small number of tumors, with differing results. The objective of this study was to determine whether reduced expression of RB and/or overexpression of hyperphosphorylated RB predict MTC aggressive behavior.

METHODS

Formalin-fixed, paraffin-embedded primary thyroid tumors and lymph node metastases from MTC patients were evaluated for calcitonin, RB, and phosphorylated RB (pRB) expression by immunohistochemistry. Two expert pathologists evaluated the slides in a blinded manner, and the immunohistochemistry results were compared to disease-specific survival as a primary endpoint.

RESULTS

Seventy-four MTC samples from 56 patients were analyzed in this study, including 51 primary tumors and 23 lymph node metastases. The median follow-up time was 6.75 years after surgery (range 0.64-24.30 years), and the median primary tumor size was 30 mm (range 6-96 mm). Sixty-six percent of cases were classified as stage IV. RB nuclear expression was diffusely present in 88% of primary tumors and 78% of lymph node metastases. Nuclear pRB expression was present in 22% of primary tumors and 22% of lymph node metastases. On univariate analysis, reduced RB (<75% tumor cell staining) trended with lower MTC-specific survival for primary tumor and metastatic nodes (primary tumor hazard ratio = 3.54 [confidence interval 0.81-15.47], p = 0.08; and lymph node hazard ratio = 4.35 [confidence interval 0.87-21.83], p = 0.05). For primary tumors, multivariable analysis showed that low nuclear RB expression was independently associated with worse disease-specific (p = 0.01) and overall (p = 0.02) survival. pRB levels were not associated with survival for either primary tumor or lymph node metastases.

CONCLUSIONS

Reduced RB expression is associated with decreased patient survival in univariate and multivariable analyses, independent from patient age at surgery or advanced TNM stage. Future studies involving larger MTC patient populations are warranted to determine if lower RB expression levels may serve as a biomarker for aggressive disease in patients with MTC.

Role of CDKN2C Fluorescence In Situ Hybridization in the Management of Medullary Thyroid Carcinoma

Medullary thyroid carcinoma (MTC), an aggressive form of thyroid cancer, occurs sporadically in approximately 75% of MTCs. RET and RAS mutations play a role in about 40% and 15%, respectively, of sporadic MTCs and are predominant drivers in MTC pathways. These mutations are some of the most comprehensively described and screened for in MTC patients; however, in recent studies, other mutations in the CDKN2C gene (p18) have been implicated in the tumorigenesis of MTC. Comparative genomic hybridization analysis revealed that approximately 40% of sporadic MTC samples have loss of CDKN2C at chromosome 1p32 in addition to frequent losses of CDKN2D (p19) at chromosome 19p13. However, no feasible routine method had been established to detect loss of heterozygosity (LOH) of CDKN2C and CD-KN2D The aim of this study is to assess the feasibility of using Fluorescence in situ Hybridization (FISH) to screen MTC patients for CDKN2C and CDKN2D deletions. We subjected 5 formalin-fixed, paraffin-embedded (FFPE) MTC samples with defined RET/RAS mutations to dual-color FISH assays to detect loss of CDKN2C and/or CDKN2D We prepared spectrum orange probes using the bacterial artificial chromosomes RP11-779F9 for CDKN2C (p18) and RP11-177J4 for CDKN2D (p19) and prepared spectrum green control probes to the 1q25.2 and 19q11 regions (RP11-1146A3 and RP11-942P7, respectively). Nine FFPE normal thyroid tissue samples were used to establish the cutoff values for the FISH signal patterns. Of the five FFPE MTC samples, four and one yielded a positive significant result for CDKNN2C loss and CDKN2D loss, respectively. The results of a Clinical Laboratory Improvement Amendments validation with a CDKN2C/CKS1B probe set for CDKN2C (p18) loss of heterozygosity were 100% concordant with the FISH results obtained in this study. Thus, FISH is a fast and reliable diagnostic or prognostic indicator of gene loss in MTC.

Cousins not twins: intratumoural and intertumoural heterogeneity in syndromic neuroendocrine tumours

Hereditary endocrine neoplasias, including phaeochromocytoma/paraganglioma and medullary thyroid cancer, are caused by autosomal dominant mutations in several familial cancer genes. A common feature of these diseases is the presentation of multiple primary tumours, or multifocal disease representing independent tumour clones that have arisen from the same initiating genetic lesion, but have undergone independent clonal evolution. Such tumours provide an opportunity to discover common cooperative changes required for tumourigenesis, while controlling for the genetic background of the individual. We performed genomic analysis of synchronous and metachronous tumours from five patients bearing germline mutations in the genes SDHB, RET, and MAX. Using whole exome sequencing and high-density single-nucleotide polymorphism arrays, we analysed two to four primary tumours from each patient. We also applied multi-region sampling, to assess intratumoural heterogeneity and clonal evolution, in two cases involving paraganglioma and medullary thyroid cancer, respectively. Heterogeneous patterns of genomic change existed between synchronous or metachronous tumours, with evidence of branching evolution. We observed striking examples of evolutionary convergence involving the same rare somatic copy-number events in synchronous primary phaeochromocytoma/paraganglioma. Convergent events also occurred during clonal evolution of metastatic medullary thyroid cancer. These observations suggest that genetic or epigenetic changes acquired early within precursor cells, or pre-existing within the genetic background of the individual, create contingencies that determine the evolutionary trajectory of the tumour. Copyright © 2017 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

ATF4 Targets RET for Degradation and Is a Candidate Tumor Suppressor Gene in Medullary Thyroid Cancer

CONTEXT

Medullary thyroid cancer (MTC) is an aggressive tumor that harbors activating mutations of the RET proto-oncogene. We previously reported that RET inhibits transcriptional activity of ATF4, the master regulator of the stress response pathway, to prevent cell death.

OBJECTIVE

We hypothesized that loss of function of ATF4 plays a role in initiation of MTC.

DESIGN

Targeted deletion of Atf4 in mice was used to assess ATF4 function in the thyroid gland. ATF4 overexpression was achieved by adenoviral and lentiviral vectors. We used immunohistochemical analysis and western blotting of MTC tumors to determine protein levels of RET and ATF4 and the Kaplan-Meier method to determine their association with clinical outcome.

RESULTS

Targeted deletion of Atf4 in mice causes C-cell hyperplasia, a precancerous lesion for MTC. Forced ATF4 expression decreased survival of MTC cells and blocked the activation of RET downstream signaling pathways (phosphorylated ERK, phosphorylated AKT, and p70S6K). ATF4 knockdown decreased sensitivity to tyrosine kinase inhibitor-induced apoptosis. Moreover, ATF4 expression decreased RET protein levels by promoting RET ubiquitination. We found decreased or loss of ATF4 in 52% of MTC tumors (n = 39) compared with normal thyroid follicle cells. A negative correlation was observed between RET and ATF4 protein levels in MTC tumors, and low ATF4 expression was associated with poor overall survival in patients with MTC.

CONCLUSIONS

ATF4 was identified as a negative regulator of RET, a candidate tumor suppressor gene, and may be a molecular marker that distinguishes patients at high risk of MTC from those with a longer survival prognosis.

Anti-tumor effects of shikonin derivatives on human medullary thyroid carcinoma cells

New treatment options are needed for medullary thyroid carcinoma (MTC), a highly metastasizing neuroendocrine tumor that is resistant to standard radiotherapy and chemotherapy. We show that the following shikonin derivatives inhibit cell proliferation and cell viability of the MTC cell line TT: acetylshikonin, β,β-dimethylacrylshikonin, shikonin and a petroleum ether extract of the roots of Onosma paniculata containing several shikonin derivatives. The unsubstituted shikonin derivative was found to be the most effective compound with an IC₅₀ of 1.1 µM. The cell viability of normal human skin fibroblasts, however, was not affected by the tested substances, indicating that shikonin derivatives might be selectively toxic for cancer cells. We further report that migration and invasion of TT cells were inhibited at non-toxic concentrations. Finally, shikonin was tested in vivo using the chick chorioallantoic membrane assay, where it significantly reduced tumor growth by inhibiting cell proliferation and inducing apoptosis. In summary, our results suggest that shikonin derivatives have the potential for the treatment of medullary thyroid carcinomas.

Role of CDKN2C Copy Number in Sporadic Medullary Thyroid Carcinoma

BACKGROUND

The cyclin-dependent-kinase inhibitors (CDKN)/retinoblastoma (RB1) pathway has been implicated as having a role in medullary thyroid carcinoma (MTC) tumorigenesis. CDKN2C loss has been associated with RET-mediated MTC in humans but with minimal phenotypic correlation provided. The objective of this study was to evaluate the association between tumor RET mutation status, CDKN2C loss, and aggressiveness of MTC in a cohort of patients with sporadic disease.

METHODS

Tumors from patients with sporadic MTC treated at a single institution were evaluated for somatic RET^M918T mutation and CDKN2C copy number loss. These variables were compared to patient demographics, pathology detail, clinical course, and disease-specific and overall survival.

RESULTS

Sixty-two MTC cases with an initial surgery date ranging from 1983 to 2009 met the inclusion criteria, of whom 36 (58%) were male. The median age at initial surgery was 53 years (range 22-81 years). The median tumor size was 30 mm (range 6-145 mm) with 29 (57%) possessing extrathyroidal extension. Nodal and/or distant metastasis at presentation was found in 47/60 (78%) and 12/61 (20%) patients, respectively. Median follow-up time was 10.5 years (range 1.1-27.8 years) for the censored observations. The presence of CDKN2C loss was associated with worse M stage and overall AJCC stage. Median overall survival of patients with versus without CDKN2C loss was 4.14 [confidence interval (CI) 1.93-NA] versus 18.27 [CI 17.24-NA] years (p < 0.0001). Median overall survival of patients with a combined somatic RET^M918T mutation and CDKN2C loss versus no somatic RET^M918T mutation and CDKN2C loss versus somatic RET^M918T mutation and CDKN2C 2N versus no somatic RET^M918T mutation and CDKN2C 2N was 2.38 [CI 1.67-NA] years versus 10.81 [CI 2.46-NA] versus 17.24 [CI 9.82-NA] versus not reached [CI 13.46-NA] years (p < 0.0001).

CONCLUSIONS

The detection of somatic CDKN2C loss is associated with the presence of distant metastasis at presentation as well decreased overall survival, a relationship enhanced by concomitant RET^M918T mutation. Further defining the genes involved in the progression of metastatic MTC will be an important step toward identifying pathways of disease progression and new therapeutic targets.

Putative BRAF activating fusion in a medullary thyroid cancer

Medullary thyroid cancer (MTC) is a malignancy of the calcitonin-producing parafollicular cells of the thyroid gland. Surgery is the only curative treatment for this cancer. External beam radiation therapy is reserved for adjuvant treatment of MTC with aggressive features. Targeted therapeutics vandetanib and cabozantinib are approved for the treatment of aggressive and metastatic tumors that are not amenable to surgery. The use of these multikinase inhibitors are supported by the observed overactivation of the RET oncoprotein in a large subpopulation of MTCs. However, not all patients carry oncogenic alterations of this kinase. Hence, there is still a need for comprehensive molecular characterization of MTC utilizing whole-genome and transcriptome-sequencing methodologies with the aim of identifying targetable mutations. Here, we describe the genomic profiles of two medullary thyroid cancers and report the presence of a putative oncogenic BRAF fusion in one. Such alterations, previously observed in other malignancies and known targets of available drugs, can benefit patients who currently have no treatment options.

Differential expression of cell cycle regulators in CDK5-dependent medullary thyroid carcinoma tumorigenesis

Medullary thyroid carcinoma (MTC) is a neuroendocrine cancer of thyroid C-cells, for which few treatment options are available. We have recently reported a role for cyclin-dependent kinase 5 (CDK5) in MTC pathogenesis. We have generated a mouse model, in which MTC proliferation is induced upon conditional overexpression of the CDK5 activator, p25, in C-cells, and arrested by interrupting p25 overexpression. Here, we identify genes and proteins that are differentially expressed in proliferating versus arrested benign mouse MTC. We find that downstream target genes of the tumor suppressor, retinoblastoma protein, including genes encoding cell cycle regulators such as CDKs, cyclins and CDK inhibitors, are significantly upregulated in malignant mouse tumors in a CDK5-dependent manner. Reducing CDK5 activity in human MTC cells down-regulated these cell cycle regulators suggesting that CDK5 activity is critical for cell cycle progression and MTC proliferation. Finally, the same set of cell cycle proteins was consistently overexpressed in human sporadic MTC but not in hereditary MTC. Together these findings suggest that aberrant CDK5 activity precedes cell cycle initiation and thus may function as a tumor-promoting factor facilitating cell cycle protein expression in MTC. Targeting aberrant CDK5 or its downstream effectors may be a strategy to halt MTC tumorigenesis.

RAS proto-oncogene in medullary thyroid carcinoma

Medullary thyroid carcinoma (MTC) is a rare malignancy originating from the calcitonin-secreting parafollicular thyroid C cells. Approximately 75% of cases are sporadic. Rearranged during transfection (RET) proto-oncogene plays a crucial role in MTC development. Besides RET, other oncogenes commonly involved in the pathogenesis of human cancers have also been investigated in MTC. The family of human RAS genes includes the highly homologous HRAS, KRAS, and NRAS genes that encode three distinct proteins. Activating mutations in specific hotspots of the RAS genes are found in about 30% of all human cancers. In thyroid neoplasias, RAS gene point mutations, mainly in NRAS, are detected in benign and malignant tumors arising from the follicular epithelium. However, recent reports have also described RAS mutations in MTC, namely in HRAS and KRAS. Overall, the prevalence of RAS mutations in sporadic MTC varies between 0-43.3%, occurring usually in tumors with WT RET and rarely in those harboring a RET mutation, suggesting that activation of these proto-oncogenes represents alternative genetic events in sporadic MTC tumorigenesis. Thus, the assessment of RAS mutation status can be useful to define therapeutic strategies in RET WT MTC. MTC patients with RAS mutations have an intermediate risk for aggressive cancer, between those with RET mutations in exons 15 and 16, which are associated with the worst prognosis, and cases with other RET mutations, which have the most indolent course of the disease. Recent results from exome sequencing indicate that, besides mutations in RET, HRAS, and KRAS, no other recurrent driver mutations are present in MTC.

Exome sequencing reveals mutant genes with low penetrance involved in MEN2A-associated tumorigenesis

Activating rearranged during transfection (RET) mutations function as the initiating causative mutation for multiple endocrine neoplasia type 2A (MEN2A). However, no conclusive findings regarding the non-RET genetic events have been reported. This is the first study, to our knowledge, examining genomic alterations in matched MEN2A-associated tumors. We performed exome sequencing and SNP array analysis of matched MEN2A tumors and germline DNA. Somatic alterations were validated in an independent set of patients using Sanger sequencing. Genes of functional interest were further evaluated. The germline RET mutation was found in all MEN2A-component tumors. Thirty-two somatic mutations were identified in the nine MEN2A-associated tumors, of which 28 (87.5%) were point mutations and 4 (12.5%) were small insertions, duplications, or deletions. We sequenced all the mutations as well as coding sequence regions of the 12 genes in an independent sample set including 35 medullary thyroid cancers (20 MEN2A) and 34 PCCs (22 MEN2A), but found no recurrent mutations. Recurrent alterations were found in 13 genes with either mutations or alterations in copy number, including an EIF4G1 mutation (p. E1147V). Mutation of EIF4G1 led to increased cell proliferation and RET/MAPK phosphorylation, while knockdown of EIF4G1 led to reduced cell proliferation and RET/MAPK phosphorylation in TT, MZ-CRC1, and PC-12 cells. We found fewer somatic mutations in endocrine tumors compared with non-endocrine tumors. RET was the primary driver in MEN2A-associated tumors. However, low-frequency alterations such as EIF4G1 might participate in MEN2A-associated tumorigenesis, possibly by regulating the activity of the RET pathway.

Thyroid C-Cell Biology and Oncogenic Transformation

The thyroid parafollicular cell, or commonly named "C-cell," functions in serum calcium homeostasis. Elevations in serum calcium trigger release of calcitonin from the C-cell, which in turn functions to inhibit absorption of calcium by the intestine, resorption of bone by the osteoclast, and reabsorption of calcium by renal tubular cells. Oncogenic transformation of the thyroid C-cell is thought to progress through a hyperplastic process prior to malignancy with increasing levels of serum calcitonin serving as a biomarker for tumor burden. The discovery that multiple endocrine neoplasia type 2 is caused by activating mutations of the RET gene serves to highlight the RET-RAS-MAPK signaling pathway in both initiation and progression of medullary thyroid carcinoma (MTC). Thyroid C-cells are known to express RET at high levels relative to most cell types; therefore, aberrant activation of this receptor is targeted primarily to the C-cell, providing one possible cause of tissue-specific oncogenesis. The role of RET signaling in normal C-cell function is unknown though calcitonin gene transcription appears to be sensitive to RET activation. Beyond RET, the modeling of oncogenesis in animals and screening of human tumors for candidate gene mutations have uncovered mutation of RAS family members and inactivation of Rb1 regulatory pathway as potential mediators of C-cell transformation. A growing understanding of how RET interacts with these pathways, both in normal C-cell function and during oncogenic transformation, will help in the development of novel molecular-targeted therapies.

Genome-wide copy number analysis in a family with p.G533C RET mutation and medullary thyroid carcinoma identified regions potentially associated with a higher predisposition to lymph node metastasis

CONTEXT

Our group described a p.G533C RET gene mutation in a large family with multiple endocrine neoplasia type 2 syndrome. Clinical heterogeneity, primarily associated with the presence of lymph node metastases, was observed among the p.G533C carriers.

OBJECTIVE

The aim of this study was to use single-nucleotide polymorphism-array technology to identify copy number variations (CNVs), which are present in the constitutional DNA and associated with the established clinical and pathological features of aggressive medullary thyroid carcinoma (MTC), primarily the presence of lymph node metastasis.

DESIGN

Fifteen p.G533C carriers with MTC were chosen for the initial screening. The subjects were divided into two groups according the presence (n = 8) or absence (n = 7) of lymph node metastasis. Peripheral blood DNA was independently hybridized using a genome-wide single-nucleotide polymorphism Array 6.0 platform. The results were analyzed using both Genotyping Console and PennCNV software. To identify the possible candidate regions associated with the presence of lymph node metastasis, cases (metastatic MTC) were compared with controls (nonmetastatic MTC). The identified CNVs were validated by quantitative PCR in an extended cohort (n = 32).

RESULTS

Using two different algorithms, we identified nine CNV regions that may contribute to susceptibility to lymph node metastasis. The validation step confirmed that a CNV loss impacting the FMN2 gene was potentially associated with a greater predisposition to lymph node metastasis in this family (P = .0179). Finally, we sought to investigate whether the development of lymph node metastasis might not depend on a single CNV but rather a combination of various CNVs. These analyses defined a CNV pattern related to a more aggressive phenotype in this family, with CNV deletions being enriched in the metastatic group (P = .0057).

CONCLUSION

Although hereditable specific RET mutations are important to determine cancer risk, germline CNVs in disease-affected individuals may predispose them to MTC aggressiveness.

The role of Cdk5 in neuroendocrine thyroid cancer

Medullary thyroid carcinoma (MTC) is a neuroendocrine cancer that originates from calcitonin-secreting parafollicular cells, or C cells. We found that Cdk5 and its cofactors p35 and p25 are highly expressed in human MTC and that Cdk5 activity promotes MTC proliferation. A conditional MTC mouse model was generated and corroborated the role of aberrant Cdk5 activation in MTC. C cell-specific overexpression of p25 caused rapid C cell hyperplasia leading to lethal MTC, which was arrested by repressing p25 overexpression. A comparative phosphoproteomic screen between proliferating and arrested MTC identified the retinoblastoma protein (Rb) as a crucial Cdk5 downstream target. Prevention of Rb phosphorylation at Ser807/Ser811 attenuated MTC proliferation. These findings implicate Cdk5 signaling via Rb as critical to MTC tumorigenesis and progression.