Lack of S37A CTNNB1/β-catenin mutations in a Swedish cohort of 98 parathyroid adenomas

Genomics and Epigenomics in Parathyroid Neoplasia: from Bench to Surgical Pathology Practice

The majority of parathyroid disease encountered in routine practice is due to single parathyroid adenoma, of which the majority arise as sporadic tumors. This is usually a straightforward diagnosis in endocrine pathology when in the appropriate clinical setting, although subsets of cases will exhibit atypical histological features that may warrant additional immunohistochemical and genetic analyses to estimate the malignant potential. Parathyroid carcinomas on the other hand, are bona fide malignant tumors characterized by their unequivocal invasion demonstrated through routine histology or metastasis. The ultimate endpoint for any molecular marker discovered through laboratory investigations is to be introduced in clinical routine practice and guide the surgical pathologist in terms of diagnostics and prognostication. For parathyroid tumors, the two main diagnostic challenges include the distinction between parathyroid adenoma and parathyroid carcinoma, as well as the pinpointing of hereditable disease for familial screening purposes. While numerous markers on genetic, epigenetic, and protein levels have been proposed as discriminative in these aspects, this review aims to condense the scientific coverage of these enigmatic topics and to propose a focused surgical pathology approach to the subject.

Effects of Arsenic on wnt/β-catenin Signaling Pathway: A Systematic Review and Meta-analysis

We aimed to systematically evaluate the regulatory effect of arsenic on wnt/β-catenin signaling pathway and to provide theoretical basis for revealing the mechanism of the relationship between arsenic and cell proliferation. The meta-analysis was carried out using Revman5.2 and Stata13.0 to describe the differences between groups with standard mean difference. We found in normal cells that the levels of wnt3a, β-catenin, glycogen synthase kinase-3β phosphorylated at serine 9 (p-GSK-3β(Ser9)), cyclinD1, proto-oncogene c-myc, and vascular endothelial growth factor (VEGF) in the arsenic intervention group were higher than those in the control group, and the level of glycogen synthase kinase-3β (GSK-3β) was lower than that in the control group (P < 0.05, respectively). Subgroup analysis showed that for a long time period (>24 h), the level of β-catenin in the arsenic intervention group was higher than that in the control group, and the level of GSK-3β of the same long-time period (>24 h) with low-dose (≤5 μM) intervention was lower than those in the control group (P < 0.05, respectively). In cancer cells, the levels of β-catenin, cyclinD1, c-myc, and VEGF in the arsenic intervention group were lower than those in the control group, while the level of GSK-3β in the arsenic intervention group was higher than that in the control group (P < 0.05, respectively). Subgroup analysis showed that the levels of β-catenin, cyclinD1, and c-myc in the high-dose (>5 μM) arsenic intervention group were lower than those in the control group, and the levels of β-catenin and cyclinD1 in the high-dose (>5 μM) arsenic intervention group were lower than those in the low-dose (≤5 μM) arsenic intervention group (P < 0.05, respectively). In addition, the regulation of arsenic on β-catenin was dose-dependent in the range of arsenic concentration from 0 to 7.5 μM. This study revealed that arsenic could upregulate wnt/β-catenin signaling pathway in normal cells and downregulate it in cancer cells, and its effect was affected by time and dose.

EZH2 and ZFX oncogenes in malignant behaviour of parathyroid neoplasms

Several studies reported somatic mutations of many genes (MEN1, CTNNB1, CDKIs and others) in parathyroid adenoma, although with different prevalence. Recently, activating mutations of the EZH2 and ZFX oncogenes were identified in benign parathyroid adenoma by whole exome sequencing. The same mutations had been found in blood and ovary malignant tumours. On one hand, this result raised the hypothesis that these oncogenes may play a role in the onset of parathyroid tumour, but it would also suggest they may be involved in malignant, rather benign, parathyroid neoplasm. Our aim was to verify the occurrence of selected mutations of the EZH2 and ZFX genes in an Italian cohort of 23 sporadic parathyroid carcinomas, 12 atypical and 45 typical adenomas. DNA was extracted from paraffin-embedded tissues, PCR amplified and directly sequenced. No mutations were detected in the coding sequence and boundaries of both genes in any of the samples. Two polymorphisms of the EZH2 gene were identified with different prevalence: the rs2072407 variant was present in the 30 % of the samples, in keeping with the overall frequency in larger populations, while the rs78589034 variant, located close to the 5' end of the exon 16, was detected in only one proband with familial isolated hyperparathyroidism; we investigated the possible outcome on the splicing process. EZH2 and ZFX genes do not seem to have an impact on the onset of most parathyroid tumours, both benign and malignant, though further studies on larger cohorts of different ethnicity are needed.

Genetic and epigenetic changes in sporadic endocrine tumors: parathyroid tumors

Parathyroid neoplasia is most commonly due to benign parathyroid adenoma but rarely can be caused by malignant parathyroid carcinoma. Evidence suggests that parathyroid carcinomas rarely, if ever, evolve through an identifiable benign intermediate, with the notable exception of carcinomas associated with the familial hyperparathyroidism-jaw tumor syndrome. Several genes have been directly implicated in the pathogenesis of typical sporadic parathyroid adenoma; somatic mutations in the MEN1 tumor suppressor gene are the most frequent finding, and alterations in the cyclin D1/PRAD1 oncogene are also firmly established molecular drivers of sporadic adenomas. In addition, good evidence supports mutation in the CDKN1B/p27 cyclin-dependent kinase inhibitor (CDKI) gene, and in other CDKI genes as contributing to disease pathogenesis in this context. Somatic defects in additional genes, including β-catenin, POT1 and EZH2 may contribute to parathyroid adenoma formation but, for most, their ability to drive parathyroid tumorigenesis remains to be demonstrated experimentally. Further, genetic predisposition to sporadic presentations of parathyroid adenoma appears be conferred by rare, and probably low-penetrance, germline variants in CDKI genes and, perhaps, in other genes such as CASR and AIP. The HRPT2 tumor suppressor gene is commonly mutated in parathyroid carcinoma.

Molecular characterization of parathyroid tumors from two patients with hereditary colorectal cancer syndromes

The tumor suppressor adenomatous polyposis coli (APC) has recently been implicated in parathyroid development. We here report clinical, histopathological and molecular investigations in parathyroid tumors arising in two patients; one familial adenomatous polyposis (FAP) syndrome patient carrying a constitutional APC mutation, and one Lynch syndrome patient demonstrating a germline MLH1 mutation as well as a non-classified, missense alteration of the APC gene. We sequenced the entire APC gene in tumor and constitutional DNA from both cases, assessed the levels of APC promoter 1A and 1B methylation by bisulfite Pyrosequencing analysis and performed immunohistochemistry for APC and parafibromin. In addition, copy number analysis regarding the APC gene on chromosome 5q21-22 was performed using qRT-PCR. Histopathological workup confirmed both tumors as parathyroid adenomas without signs of malignancy or atypia. No somatic mutations or copy number changes for the APC gene were discovered in the tumors; however, in both cases, the APC promoter 1A was hypermethylated while the APC promoter 1B was unmethylated. APC promoter 1B-specific mRNA and total APC mRNA levels were higher than in normal parathyroid samples. Immunohistochemical analyses revealed strong APC protein immunoreactivity and positive parafibromin expression in both parathyroid tumors. Absence of additional somatic APC mutations and copy number changes in addition to the positive APC immunoreactivity obtained suggest that the tumors arose without biallelic inactivation of the APC tumor suppressor gene. The finding of an unmethylated APC promoter 1B and high APC 1B mRNA levels could explain the maintained APC protein expression. Moreover, the findings of positive parafibromin and APC immunoreactivity as well as a low MIB-1 proliferation index and absence of histopathological features of malignancy/atypical adenoma indicate that the parathyroid adenomas arising in these patients did not harbor malignant potential.

Whole-exome sequencing studies of nonhereditary (sporadic) parathyroid adenomas

CONTEXT

Genetic abnormalities, such as those of multiple endocrine neoplasia type 1 (MEN1) and Cyclin D1 (CCND1) genes, occur in <50% of nonhereditary (sporadic) parathyroid adenomas.

OBJECTIVE

To identify genetic abnormalities in nonhereditary parathyroid adenomas by whole-exome sequence analysis.

DESIGN

Whole-exome sequence analysis was performed on parathyroid adenomas and leukocyte DNA samples from 16 postmenopausal women without a family history of parathyroid tumors or MEN1 and in whom primary hyperparathyroidism due to single-gland disease was cured by surgery. Somatic variants confirmed in this discovery set were assessed in 24 other parathyroid adenomas.

RESULTS

Over 90% of targeted exons were captured and represented by more than 10 base reads. Analysis identified 212 somatic variants (median eight per tumor; range, 2-110), with the majority being heterozygous nonsynonymous single-nucleotide variants that predicted missense amino acid substitutions. Somatic MEN1 mutations occurred in six of 16 (∼35%) parathyroid adenomas, in association with loss of heterozygosity on chromosome 11. However, no other gene was mutated in more than one tumor. Mutations in several genes that may represent low-frequency driver mutations were identified, including a protection of telomeres 1 (POT1) mutation that resulted in exon skipping and disruption to the single-stranded DNA-binding domain, which may contribute to increased genomic instability and the observed high mutation rate in one tumor.

CONCLUSIONS

Parathyroid adenomas typically harbor few somatic variants, consistent with their low proliferation rates. MEN1 mutation represents the major driver in sporadic parathyroid tumorigenesis although multiple low-frequency driver mutations likely account for tumors not harboring somatic MEN1 mutations.

Genetic characterization of large parathyroid adenomas

In this study, we genetically characterized parathyroid adenomas with large glandular weights, for which independent observations suggest pronounced clinical manifestations. Large parathyroid adenomas (LPTAs) were defined as the 5% largest sporadic parathyroid adenomas identified among the 590 cases operated in our institution during 2005-2009. The LPTA group showed a higher relative number of male cases and significantly higher levels of total plasma and ionized serum calcium (P<0.001). Further analysis of 21 LPTAs revealed low MIB1 proliferation index (0.1-1.5%), MEN1 mutations in five cases, and one HRPT2 (CDC73) mutation. Total or partial loss of parafibromin expression was observed in ten tumors, two of which also showed loss of APC expression. Using array CGH, we demonstrated recurrent copy number alterations most frequently involving loss in 1p (29%), gain in 5 (38%), and loss in 11q (33%). Totally, 21 minimal overlapping regions were defined for losses in 1p, 7q, 9p, 11, and 15q and gains in 3q, 5, 7p, 8p, 16q, 17p, and 19q. In addition, 12 tumors showed gross alterations of entire or almost entire chromosomes most frequently gain of 5 and loss of chromosome 11. While gain of 5 was the most frequent alteration observed in LPTAs, it was only detected in a small proportion (4/58 cases, 7%) of parathyroid adenomas. A significant positive correlation was observed between parathyroid hormone level and total copy number gain (r=0.48, P=0.031). These results support that LPTAs represent a group of patients with pronounced parathyroid hyperfunction and associated with specific genomic features.