Novel chromosomal abnormalities identified by comparative genomic hybridization in parathyroid adenomas

Familial Hyperparathyroidism

Regulation of the serum calcium level in humans is achieved by the endocrine action of parathyroid glands working in concert with vitamin D and a set of critical target cells and tissues including osteoblasts, osteoclasts, the renal tubules, and the small intestine. The parathyroid glands, small highly vascularized endocrine organs located behind the thyroid gland, secrete parathyroid hormone (PTH) into the systemic circulation as is needed to keep the serum free calcium concentration within a tight physiologic range. Primary hyperparathyroidism (HPT), a disorder of mineral metabolism usually associated with abnormally elevated serum calcium, results from the uncontrolled release of PTH from one or several abnormal parathyroid glands. Although in the vast majority of cases HPT is a sporadic disease, it can also present as a manifestation of a familial syndrome. Many benign and malignant sporadic parathyroid neoplasms are caused by loss-of-function mutations in tumor suppressor genes that were initially identified by the study of genomic DNA from patients who developed HPT as a manifestation of an inherited syndrome. Somatic and inherited mutations in certain proto-oncogenes can also result in the development of parathyroid tumors. The clinical and genetic investigation of familial HPT in kindreds found to lack germline variants in the already known HPT-predisposition genes represents a promising future direction for the discovery of novel genes relevant to parathyroid tumor development.

Intratumor heterogeneity in human parathyroid tumors

Parathyroid tumors are the second most common endocrine neoplasia after thyroid neoplasia. They are mostly associated with impaired parathormone (PTH) synthesis and release determining the metabolic and clinical condition of primary hyperparathyroidism (PHPT). PHPT is the third most prevalent endocrine disorder, mainly affecting postmenopausal women. Parathyroid benign tumors, both adenomas of a single gland or hyperplasia involving all the glands, are the main histotypes, occurring in more than 95% of PHPT cases. The differential diagnosis between benign and malignant parathyroid lesions is a challenge for clinicians. It relies on histologic features, which display significant overlap between the histotypes with different clinical outcomes. Parathyroid adenomas and hyperplasia have been considered so far as a unique monoclonal/polyclonal entity, while accumulating evidence suggest great heterogeneity. Intratumor parathyroid heterogeneity involves tumor cell type, as well as tumor cell function, in terms of PTH synthesis and secretion, and of expression patterns of membrane and nuclear receptors (calcium sensing receptor, vitamin D receptor, α-klotho receptor and others). Intratumor heterogeneity can also interfere with cell molecular biology, in regard to clonality, oncosuppressor gene expression (such as MEN1 and HRPT2/CDC73), transcription factors (GCM2, TBX1) and microRNA expression. Such heterogeneity is likely involved in the phenotypic variability of the parathyroid tumors, and it should be considered in the clinical management, though at present target therapies are not available, with the exception of the calcium sensing receptor agonists.

Genetics of Hyperparathyroidism, Including Parathyroid Cancer

Primary hyperparathyroidism (HPT) is a metabolic disease caused by the excessive secretion of parathyroid hormone from 1 or more neoplastic parathyroid glands. HPT is largely sporadic, but it can be associated with a familial syndrome. The study of such families led to the discovery of tumor suppressor genes whose loss of function is now recognized to underlie the development of many sporadic parathyroid tumors. Heritable and acquired oncogenes causing parathyroid neoplasia are also known. Studies of somatic changes in parathyroid tumor DNA and investigation of kindreds with unexplained familial HPT promise to unmask more genes relevant to parathyroid neoplasia.

MicroRNA deregulation in parathyroid tumours suggests an embryonic signature

Primary hyperparathyroidism is a common endocrine disorder caused by abnormal tumour parathyroid cell proliferation. Parathyroid tumours show a great variability both in clinical features, such as the severity of PTH secretion, the rate and the pattern of cell proliferation, and genetic background. Studies aiming to develop new diagnostic markers and therapeutic approaches need a deeper definition of this variability. Dysregulation of microRNAs (miRNAs) has been shown to play an essential role in the development and progression of cancer. MiRNAs are small noncoding RNAs that inhibit the translation and stability of messenger RNAs (mRNAs). Here, data about the miRNA expression pattern in parathyroid normal and tumour glands were reviewed. Though available data in parathyroid tumours are very limited, the expression pattern of a subset of specific miRNAs clearly discriminated parathyroid carcinomas from normal parathyroid glands and, more clinically relevant, from parathyroid adenomas. Investigation showed that parathyroid tumours were characterized by an embryonic expression pattern of miRNAs such as miR-296, or the miRNA clusters C19MC and miR-371-3, typically in stem cells committed to differentiation or during human embryonic development, respectively. Further, miRNA profiles were correlated with tumour aggressive behaviour. Moreover, the interaction with the oncosuppressor menin suggests that miRNAs might modulate the function of the known oncosuppressors or oncogenes involved in parathyroid tumourigenesis and thus overseeing the tumour phenotype. In conclusion, miRNAs might provide new diagnostic markers and new therapeutic approaches by developing molecular miRNA-targeted therapies for the cure of parathyroid tumours, whose unique option is surgery.

Recurrent ZFX mutations in human sporadic parathyroid adenomas

The molecular abnormalities leading to sporadic parathyroid adenomas, a common type of human endocrine neoplasm, are heterogeneous and incompletely understood. Using whole exome and direct sequencing of parathyroid adenoma DNA samples, we identified recurrent somatic mutations in the ZFX gene. ZFX is a member of Krueppel C2H2 type zinc finger protein family, was initially described as a homolog of ZFY, and has been implicated as a transcription factor regulating embryonic stem cell renewal. The ZFX mutations we identified were strikingly specific, focused in each tumor on one encoded residue in a hotspot of two consecutive highly conserved arginine residues (R786/787; arginine to glutamine, threonine or leucine) in a zinc finger domain near the C-terminus of the protein. The intragenic specificity of these recurrently selected mutations, their confirmed expression within the tumors, the absence of loss of heterozygosity, and the absence of these mutations among over 4000 ZFX alleles in the dbSNP137 database, strongly suggest a novel role for ZFX as a human proto-oncogene. Further, these observations highlight the mutated zinc-finger domain as a new focal point for understanding ZFX's normal and tumorigenic functions, and for development of molecularly-targeted therapeutics.

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.

Allelic imbalance in sporadic parathyroid carcinoma and evidence for its de novo origins

Parathyroid cancer is a rare, clinically aggressive cause of primary hyperparathyroidism, and whether these malignancies generally evolve from pre-existing benign adenomas or arise de novo is unclear. Furthermore, while inactivation of the CDC73 (HRPT2) tumor suppressor gene, encoding parafibromin, is a major contributor, other genes essential to parathyroid carcinogenesis remain unknown. We sought to identify genomic regions potentially harboring such oncogenes or tumor suppressor genes, and to gain insight into the origins and molecular relationship of malignant versus benign parathyroid tumors. We performed genome-wide copy-number and loss of heterozygosity analysis using Affymetrix 50K SNP mapping arrays and/or comparative genomic hybridization on 16 primary parathyroid carcinomas, local recurrences or distant metastases, and matched normal controls, from 10 individuals. Recurrent regions of allelic loss were observed on chromosomes 1p, 3, and 13q suggesting that key parathyroid tumor suppressor genes are located in these chromosomal locations. Recurrent allelic gains were seen on chromosomes 1q and 16, suggesting the presence of parathyroid oncogenes on these chromosomes. Importantly, the most common alteration in benign parathyroid adenomas, loss of 11q, was not found as a recurrent change in the malignant parathyroid tissues. Molecular allelotyping using highly polymorphic microsatellite markers provided further confirmation that the prevalence of 11q loss is markedly and significantly lower in carcinomas as compared with adenomas. Our observations provide molecular support for the concept that sporadic parathyroid cancer usually arises de novo, rather than evolving from a pre-existing typical benign adenoma. Furthermore, these results help direct future investigation to ultimately determine which of the candidate genes in these chromosomal locations make significant contributions to the molecular pathogenesis of parathyroid cancer.

Genome-wide and locus specific alterations in CDC73/HRPT2-mutated parathyroid tumors

Mutations in the hyperparathyroidism type 2 (HRPT2/CDC73) gene and alterations in the parafibromin protein have been established in the majority of parathyroid carcinomas and in subsets of parathyroid adenomas. While it is known that CDC73-mutated parathyroid tumors display specific gene expression changes compared to CDC73 wild-type cases, the molecular cytogenetic profile in CDC73-mutated cases compared to unselected adenomas (with an expected very low frequency of CDC73 mutations) remains unknown. For this purpose, nine parathyroid tumors with established CDC73 gene inactivating mutations (three carcinomas, one atypical adenoma and five adenomas) were analyzed for copy number alterations and loss of heterozygosity using array-comparative genomic hybridization (a-CGH) and single nucleotide polymorphism (SNP) microarrays, respectively. Furthermore, CDC73 gene promoter methylation levels were assessed using bisulfite Pyrosequencing. The panel included seven tumors with single mutation and three with double mutations of the CDC73 gene. The carcinomas displayed copy number alterations in agreement with previous studies, whereas the CDC73-mutated adenomas did not display the same pattern of alterations at loci frequently deleted in unselected parathyroid tumors. Furthermore, gross losses of chromosomal material at 1p and 13 were significantly (p = 0.012) associated with parathyroid carcinomas as opposed to adenomas. Quantitative PCR-based copy number loss regarding CDC73 was observed in three adenomas, while all the carcinomas were diploid or showed copy number gain for CDC73 gene. Hypermethylation of the CDC73 gene promoter was not observed. Our data could suggest that CDC73-mutated parathyroid adenomas exhibit a partly unique cytogenetic profile in addition to that of carcinomas and unselected adenomas. Furthermore, CDC73-mutated carcinomas displayed losses at 1p and 13 which are not seen in CDC73-mutated adenomas, making these regions of interest for further studies regarding malignant properties in tumors from CDC73-mutated cases. However, due to the small sample size, validation of the results in a larger cohort is warranted.

Identification of somatic mutations in parathyroid tumors using whole-exome sequencing

CONTEXT

The underlying molecular alterations causing sporadic parathyroid adenomas that drive primary hyperparathyroidism have not been thoroughly defined.

OBJECTIVE

The aim of the study was to investigate the occurrence of somatic mutations driving tumor formation and progression in sporadic parathyroid adenoma using whole-exome sequencing.

DESIGN

Eight matched tumor-constitutional DNA pairs from patients with sporadic parathyroid adenomas underwent whole-exome capture and high-throughput sequencing. Selected genes were analyzed for mutations in an additional 185 parathyroid adenomas.

RESULTS

Four of eight tumors displayed a frame shift deletion or nonsense mutation in MEN1, which was accompanied by loss of heterozygosity of the remaining wild-type allele. No other mutated genes were shared among the eight tumors. One tumor harbored a Y641N mutation of the histone methyltransferase EZH2 gene, previously linked to myeloid and lymphoid malignancy formation. Targeted sequencing in the additional 185 parathyroid adenomas revealed a high rate of MEN1 mutations (35%). Furthermore, this targeted sequencing identified an additional parathyroid adenoma that contained the identical, somatic EZH2 mutation that was found by exome sequencing.

CONCLUSION

This study confirms the frequent role of the loss of heterozygosity of chromosome 11 and MEN1 gene alterations in sporadic parathyroid adenomas and implicates a previously unassociated methyltransferase gene, EZH2, in endocrine tumorigenesis.

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.

Molecular alterations in sporadic primary hyperparathyroidism

Primary hyperparathyroidism (PHPT) is a frequent endocrine disorder characterized by an excessive autonomous production and release of parathyroid hormone (PTH) by the parathyroid glands. This endocrinopathy may result from the development of a benign lesion (adenoma or hyperplasia) or from a carcinoma. Most of the PHPT cases occur sporadically; however, approximately 10% of the patients present a familial form of the disease. The molecular mechanisms underlying the pathogenesis of sporadic PHPT are incompletely understood, even though somatic alterations in MEN1 gene and CCND1 protein overexpression are frequently observed. The MEN1 gene is mutated in about 30% of the parathyroid tumours and the protooncogene CCND1 is implicated in parathyroid neoplasia by rearrangements, leading to an overexpression of CCND1 protein in parathyroid cells. The aim of this work is to briefly update the molecular alterations underlying sporadic primary hyperparathyroidism.

Clinical and molecular genetics of parathyroid neoplasms

Primary hyperparathyroidism (HPT) results from the excessive secretion of parathyroid hormone from parathyroid tumours. While most HPT is sporadic, it is associated with a familial syndrome in a minority of cases. The study of these syndromes has helped define the pathophysiology of both familial and sporadic parathyroid neoplasms. Investigation of kindred with multiple endocrine neoplasia type 1 (MEN1) and the hyperparathyroidism-jaw tumour syndrome (HPT-JT) led to the discovery of the tumour suppressor genes MEN1 and HRPT2. We now recognise that somatic mutations in MEN1 and HRPT2 tumour suppressor genes are frequent events in sporadic parathyroid adenomas and carcinomas, respectively. Parathyroid tumours in the MEN2A syndrome result from mutational activation of the RET oncogene. The CCND1/PRAD1 oncogene was discovered by analysis of sporadic parathyroid tumours. Studies of familial isolated HPT and analysis of chromosomal loss and gain in parathyroid tumours suggest that other genes relevant to parathyroid neoplasia await identification.

Analysis of CYP27B1, encoding 25-hydroxyvitamin D-1alpha-hydroxylase, as a candidate tumor suppressor gene in primary and severe secondary/tertiary hyperparathyroidism

CYP27B1, encoding 25-hydroxyvitamin D-1alpha-hydroxylase, converts 25-hydroxyvitamin D to its active form, 1,25-dihydroxyvitamin D, and is expressed primarily in the kidney but also in nontraditional sites including the parathyroid glands. Whereas the role of locally produced 1,25-dihydroxyvitamin D is not yet clear, it is possible that it contributes importantly to vitamin D-mediated inhibition of parathyroid cell growth, so CYP27B1 can be considered a candidate parathyroid tumor suppressor gene in that its acquired inactivation in a parathyroid cell could confer a tumorigenic growth advantage. Expression of CYP27B1 has also been reported to be altered in parathyroid neoplasms. Because detection of inactivating mutations is the central criterion for validating a candidate tumor suppressor, we directly sequenced the coding region and all splice sites of CYP27B1 in 31 sporadic parathyroid adenomas and 31 parathyroid tumors from patients with refractory secondary/tertiary hyperparathyroidism. No nonsense, frameshift, or other inactivating mutations were found, and there was no sign of homozygous deletion. Our findings indicate that CYP27B1 does not commonly serve as a classical tumor suppressor gene in the development of sporadic parathyroid adenomas or of refractory secondary/tertiary hyperparathyroidism.

Genetic testing in familial isolated hyperparathyroidism: unexpected results and their implications

Familial hyperparathyroidism is not uncommon in clinical endocrine practice. It encompasses a spectrum of disorders including multiple endocrine neoplasia types 1 (MEN1) and 2A, hyperparathyroidism-jaw tumour syndrome (HPT-JT), familial hypocalciuric hypercalcaemia (FHH), and familial isolated hyperparathyroidism (FIHP). Distinguishing among the five syndromes is often difficult but has profound implications for the management of patient and family. The availability of specific genetic testing for four of the syndromes has improved diagnostic accuracy and simplified family monitoring in many cases but its current cost and limited accessibility require rationalisation of its use. No gene has yet been associated exclusively with FIHP. FIHP phenotypes have been associated with mutant MEN1 and calcium-sensing receptor (CASR) genotypes and, very recently, with mutation in the newly identified HRPT2 gene. The relative proportions of these are not yet clear. We report results of MEN1, CASR, and HRPT2 genotyping of 22 unrelated subjects with FIHP phenotypes. We found 5 (23%) with MEN1 mutations, four (18%) with CASR mutations, and none with an HRPT2 mutation. All those with mutations had multiglandular hyperparathyroidism. Of the subjects with CASR mutations, none were of the typical FHH phenotype. These findings strongly favour a recommendation for MEN1 and CASR genotyping of patients with multiglandular FIHP, irrespective of urinary calcium excretion. However, it appears that HRPT2 genotyping should be reserved for cases in which other features of the HPT-JT phenotype have occurred in the kindred. Also apparent is the need for further investigation to identify additional genes associated with FIHP.

Independent genetic events associated with the development of multiple parathyroid tumors in patients with primary hyperparathyroidism

Multiple parathyroid tumors, as opposed to hyperplasia, have been reported in a subset of patients with sporadic primary hyperparathyroidism (PHPT). It is not clear whether these multiple tumors are representative of a neoplastic process or whether they merely represent hyperplasia that has affected the parathyroid glands differentially and resulted in asynchronous growth. The molecular genetic techniques of comparative genomic hybridization (CGH), loss of heterozygosity (LOH), and MEN1 mutation analysis were performed on a series of five patients with multiglandular PHPT, each of which had two parathyroid tumors removed. Analysis of these multiple parathyroid tumors from patients with PHPT revealed that independent genetic events were associated with the development of a subset of these tumors. The DNA sequence copy number changes, identified by CGH analyses, either involved different chromosomal regions in the paired glands of a patient (two patients), or those regions implicated in one gland were not changed in a second gland from the same patient (two patients). Each of the three patients exhibiting LOH demonstrated different changes between the paired glands. Where LOH was detected in one gland from a patient, the other gland from the same patient either exhibited no allelic loss or the loss detected was in another region. Each of the three tumors exhibiting LOH at 11q13 was found to contain a somatic MEN1 mutation in the remaining allele, however these mutations were not present in the germline or in the paired gland from the same patient. Although it is possible that a separate series of genetic changes has arisen randomly in two separate glands within the same individual, it seems more likely that the development of these multiple tumors has arisen because of the involvement of other unknown factors. These factors may be genetic [such as the involvement of one or more germline mutations in an unknown low-penetrance gene(s), germline mosaicism or alterations in calcium-sensing receptor gene(s)], epigenetic, physiological, or environmental.

Primary hyperparathyroidism caused by parathyroid-targeted overexpression of cyclin D1 in transgenic mice

The relationship between abnormal cell proliferation and aberrant control of hormonal secretion is a fundamental and poorly understood issue in endocrine cell neoplasia. Transgenic mice with parathyroid-targeted overexpression of the cyclin D1 oncogene, modeling a gene rearrangement found in human tumors, were created to determine whether a primary defect in this cell-cycle regulator can cause an abnormal relationship between serum calcium and parathyroid hormone response, as is typical of human primary hyperparathyroidism. We also sought to develop an animal model of hyperparathyroidism and to examine directly cyclin D1's role in parathyroid tumorigenesis. Parathyroid hormone gene regulatory region--cyclin D1 (PTH--cyclin D1) mice not only developed abnormal parathyroid cell proliferation, but also developed chronic biochemical hyperparathyroidism with characteristic abnormalities in bone and, notably, a shift in the relationship between serum calcium and PTH. Thus, this animal model of human primary hyperparathyroidism provides direct experimental evidence that overexpression of the cyclin D1 oncogene can drive excessive parathyroid cell proliferation and that this proliferative defect need not occur solely as a downstream consequence of a defect in parathyroid hormone secretory control by serum calcium, as had been hypothesized. Instead, primary deregulation of cell-growth pathways can cause both the hypercellularity and abnormal control of hormonal secretion that are almost inevitably linked together in this common disorder.

Deletion of 11q23 and cyclin D1 overexpression are frequent aberrations in parathyroid adenomas

Hyperparathyroidism may result from parathyroid hyperplasia or adenoma, or rarely from parathyroid carcinoma. Pericentromeric inversion of chromosome 11 that results in activation of the P:RAD1/cyclin D1 gene and tumor suppressor gene loss have been described as genetic abnormalities in the evolution of parathyroid neoplasms. We studied tissue samples taken from primary parathyroid hyperplasia, parathyroid adenoma, and histologically normal parathyroid tissue by comparative genomic hybridization, fluorescent in situ hybridization, and immunohistochemistry for cyclin D1. DNA copy number changes were infrequent in primary hyperplasia (4 of 24, 17%), but common in adenomas (10 of 16, 63%; P: = 0.0059). The most common change was deletion of the entire chromosome 11 or a part of it, with a minimal common region at 11q23. This change was present in five (31%) adenomas and two (8%) primary hyperplasias. Fluorescent in situ hybridization confirmed the presence of both MEN1 alleles located at 11q13 despite deletion of 11q23 in all three cases studied. Cyclin D1 was overexpressed in six (40%) of the 15 adenomas studied, whereas none of the 27 hyperplasias (P: = 0.0010) nor the five histologically normal tissue samples overexpressed cyclin D1. Either DNA copy number loss or cyclin D1 overexpression was present in 13 (81%) of the 16 adenomas. We conclude that DNA copy number loss and cyclin D1 overexpression are common in parathyroid adenomas. The region 11q23 is frequently lost in parathyroid adenomas and occasionally in parathyroid hyperplasias, and this suggests the possibility that a tumor suppressor gene that is important in their pathogenesis is present on 11q23.

Molecular mechanisms of primary hyperparathyroidism

Several advances have been achieved toward the goal of understanding the molecular basis of parathyroid tumorigenesis. The cyclin D1/PRAD1 oncogene has been identified, and is involved in the development of several different tumor types besides those of the parathyroid. The tumor suppressor RB gene has been linked to the pathogenesis of parathyroid carcinoma. The MEN-1 gene product has been identified and mutations in MENIN shown to contribute to sporadic tumors. An understanding of the functions of MENIN will provide further insights into parathyroid disease. Mutations in the RET gene have been identified as the causal agent in MEN-2 but this gene contributes rarely to development of sporadic parathyroid tumors. Ultimately, a description of parathyroid tumorigenesis will need to account for such features as the rarity of parathyroid carcinoma, the increased incidence of tumors after neck irradiation, and the increased frequency of hyperparathyroidism in postmenopausal women. In addition, the relationship between excessive cellular proliferation and an altered set-point in the mechanism linking extracellular calcium concentration to PTH secretion requires explanation. While mutations in the CASR gene itself play a critical role in familial disease, they do not appear to be involved in sporadic parathyroid tumorigenesis, and investigation of genes important for its expression is clearly warranted.

Patterns of chromosomal imbalances in parathyroid carcinomas

In this study we have characterized chromosomal imbalances in a panel of 29 parathyroid carcinomas using comparative genomic hybridization (CGH). The most frequently detected imbalances were losses of 1p and 13q that were seen in >40% of the cases. The commonly occurring regions of loss were assigned to 1p21-p22 (41%), 13q14-q31 (41%), 9p21-pter (28%), 6q22-q24 (24%), and 4q24 (21%), whereas gains preferentially involved 19p (45%), Xc-q13 (28%), 9q33-qter (24%), 1q31-q32 (21%) and 16p (21%). The distribution of CGH alterations supports the idea of a progression of genetic events in the development of parathyroid carcinoma, where gains of Xq and 1q would represent relatively early events that are followed by loss of 13q, 9p, and 1p, and by gain of 19p. A sex-dependent distribution was also evident for two of the common alterations with preferential gain of 1q in female cases and of Xq in male cases. When the CGH profiles for the 29 carcinomas were compared with our previously published results for sporadic parathyroid adenomas, highly significant differences were revealed. Loss of 1p, 4q, and 13q as well as gains of 1q, 9q, 16p, 19p and Xq were significantly more common in the carcinomas than in the adenomas. In contrast, loss of the 11q13 region, which is the most common CGH abnormality in sporadic adenomas, was not detected in any of the carcinomas. Taken together, the findings identify several candidate locations for tumor suppressor genes and oncogenes that are potentially involved in parathyroid carcinogenesis.