Functional characterization of novel germline TP53 variants in Swedish families.

Pathogenic germline TP53 variants predispose to a wide range of early onset cancers, often recognized as the Li-Fraumeni syndrome (LFS). They are also identified in 1% of families with hereditary breast cancer (HrBC) that do not fulfill the criteria for LFS. In this study, we present a total of 24 different TP53 variants identified in 31 Swedish families with LFS or HrBC. Ten of these variants, nine exonic and one splice, have previously not been described as germline pathogenic variants. The nine exonic variants were functionally characterized and demonstrated partial transactivation activity compared to wild-type p53. Some show nuclear localization similar to wild-type p53 while others possess cytoplasmic or perinuclear localization. The four frameshift variants (W91Gfs*32, L111 Wfs*12, S227 Lfs*20 and S240Kfs*25) had negligible, while F134 L and T231del had low level of p53 activity. The L111 Wfs*12 and T231del variants are also deficient for induction of apoptosis. The missense variant R110C retain p53 effects and the nonsense E349* shows at least partial transcription factor activity but has reduced ability to trigger apoptosis. This is the first functional characterization of novel germline TP53 pathogenic or likely pathogenic variants in the Swedish cohort as an attempt to understand its association with LFS and HrBC, respectively.

Regional differences in somatostatin receptor 2 (SSTR2) immunoreactivity is coupled to level of bowel invasion in small intestinal neuroendocrine tumors.

OBJECTIVE: Somatostatin receptor (SSTR) expression constitutes a pivotal cornerstone for accurate radiological detection and medical treatment of small intestinal neuroendocrine tumors (SI-NETs), and the development of somatostatin analogues for these purposes have revolutionized the clinical work-up. Previous assessments of SSTR isoform expression in SI-NETs have found correlations to overall prognosis and treatment response, however these analyses usually report overall tumoral immunoreactivity, and little is reported regarding histo-regional differences in expressional patterns. METHODS: Thirty-seven primary SI-NETs (WHO grade I, n=32 and WHO grade II, n=5) were collected and assessed for SSTR2 immunohistochemistry. Samples were stratified with regards to histological level of bowel infiltration and spread (mucosal region, muscularis propria region, subserosal region) and each of these tumoral regions was separately scored by SSTR2 staining localization (membrane, cytoplasmic), overall staining intensity and local staining differences within each region. RESULTS: SSTR2 immunoreactivity was progressively weaker as the tumor cells advanced through the small intestinal layers. This was exemplified by a reduction in the amount of tumor samples with strong SSTR2 expression in the deeper histological levels of the section; 56% of tumors displayed strong SSTR2 expression in the mucosal region, as compared to 29% and 30% of tumors within muscularis propria and subserosal layers, respectively. CONCLUSIONS: This observation indicates a down-regulation of SSTR2 expression as the tumors progress through the intestinal wall, which might signify underlying biological processes of importance for SI-NET invasion behavior.

TERT Promoter Hypermethylation in Gastrointestinal Cancer: A Potential Stool Biomarker.

BACKGROUND: There is a high demand for noninvasive screening tools for gastrointestinal cancer (GIC) detection, and GIC-specific markers are required for such purposes. It is established that induction of the telomerase reverse transcriptase gene (TERT) coupled with telomerase activation is essential for cancer development/progression and aberrant TERT promoter methylation of specific 5'-C-phosphate-G-3' (CpGs) has been linked to TERT induction in oncogenesis. Here we analyzed TERT promoter methylation in fecal samples from GIC patients and healthy adults and determined its value as a stool biomarker for GIC detection. MATERIALS AND METHODS: Sixty-nine GIC patients (34 colorectal carcinoma and 35 gastric cancer) and 62 healthy adults were recruited and fecal samples were collected. Paired tumors and adjacent non-cancerous tissues from 34 patients and normal mucosa tissues from 12 healthy individuals were collected. TERT promoter methylation density was determined using pyrosequencing. RESULTS: We identified two GIC-specific methylation sites at -218 (CpG site 1) and -210 (CpG site 2) in the TERT promoter in tumor tissues. Methylated TERT promoter CpG sites 1 and 2 were also detectable in patient stool, while only background levels were observed in healthy individuals. The overall sensitivity reached 52.2% (95% confidence interval [CI]: 48.3-56.0) for fecal methylated TERT promoter assays at 90% specificity, which was comparable to other known stool methylation markers for GIC detection. The combined assays of fecal TERT promoter methylation and occult blood (OB) significantly improved sensitivity and specificity in colorectal cancer (area under curves for methylation alone: 0.798, 95% CI: 0.707-0.889 vs. methylation + OB: 0.920, 95% CI: 0.859-0.981; p = .028), but not in gastric cancer. CONCLUSION: This proof-of-concept study suggests the feasibility of stool TERT promoter methylation analyses as an additional tool in noninvasive GIC screening. IMPLICATIONS FOR PRACTICE: Induction of telomerase reverse transcriptase (TERT) expression coupled with telomerase activation is essential for cancer development/progression, while aberrant TERT promoter methylation has been linked to TERT induction in oncogenesis. We identified two cancer-specific methylation sites (CpG1 and 2) in the TERT promoter in tumors from GIC patients. Methylated TERT promoter CpG sites 1 and 2 were detectable in patient stool, while only background levels were observed in healthy individuals. The sensitivity and specificity was comparable to other known stool methylation markers for GIC detection. This proof-of-concept study suggests the feasibility of stool TERT promoter methylation analyses for noninvasive screening of GIC.

Copy number alterations in small intestinal neuroendocrine tumors determined by array comparative genomic hybridization.

BACKGROUND: Small intestinal neuroendocrine tumors (SI-NETs) are typically slow-growing tumors that have metastasized already at the time of diagnosis. The purpose of the present study was to further refine and define regions of recurrent copy number (CN) alterations (CNA) in SI-NETs. METHODS: Genome-wide CNAs was determined by applying array CGH (a-CGH) on SI-NETs including 18 primary tumors and 12 metastases. Quantitative PCR analysis (qPCR) was used to confirm CNAs detected by a-CGH as well as to detect CNAs in an extended panel of SI-NETs. Unsupervised hierarchical clustering was used to detect tumor groups with similar patterns of chromosomal alterations based on recurrent regions of CN loss or gain. The log rank test was used to calculate overall survival. Mann-Whitney U test or Fisher's exact test were used to evaluate associations between tumor groups and recurrent CNAs or clinical parameters. RESULTS: The most frequent abnormality was loss of chromosome 18 observed in 70% of the cases. CN losses were also frequently found of chromosomes 11 (23%), 16 (20%), and 9 (20%), with regions of recurrent CN loss identified in 11q23.1-qter, 16q12.2-qter, 9pter-p13.2 and 9p13.1-11.2. Gains were most frequently detected in chromosomes 14 (43%), 20 (37%), 4 (27%), and 5 (23%) with recurrent regions of CN gain located to 14q11.2, 14q32.2-32.31, 20pter-p11.21, 20q11.1-11.21, 20q12-qter, 4 and 5. qPCR analysis confirmed most CNAs detected by a-CGH as well as revealed CNAs in an extended panel of SI-NETs. Unsupervised hierarchical clustering of recurrent regions of CNAs revealed two separate tumor groups and 5 chromosomal clusters. Loss of chromosomes 18, 16 and 11 and gain of chromosome 20 were found in both tumor groups. Tumor group II was enriched for alterations in chromosome cluster-d, including gain of chromosomes 4, 5, 7, 14 and gain of 20 in chromosome cluster-b. Gain in 20pter-p11.21 was associated with short survival. Statistically significant differences were observed between primary tumors and metastases for loss of 16q and gain of 7. CONCLUSION: Our results revealed recurrent CNAs in several candidate regions with a potential role in SI-NET development. Distinct genetic alterations and pathways are involved in tumorigenesis of SI-NETs.

Alternative mRNA Splicing Controls the Functions of the Histone H3K27 Demethylase UTX/KDM6A.

The UTX/KDM6A histone H3K27 demethylase plays an important role in development and is frequently mutated in cancers such as urothelial cancer. Despite many studies on UTX proteins, variations in mRNA splicing have been overlooked. Using Nanopore sequencing, we present a comprehensive analysis of UTX/KDM6A splicing events in human cell lines and in tissue samples from bladder cancer cases and normal epithelia. We found that the central region of UTX mRNAs encoded by exons 12 to 17 undergoes extensive alternative splicing. Up to half of all stable mRNAs (8-48% in bladder tissues and 18-58% in cell lines) are represented by the UTX canonical isoform lacking exon 14 encoding a nuclear localization sequence, and hence exon 14-containing UTX isoforms exclusively localize to the nucleus, unlike the cytonuclear localization of the canonical isoform. Chromatin association was also higher for exon-14-containing isoforms compared to the canonical UTX. Using quantitative mass spectrometry, we found that all UTX isoforms integrated into the MLL3 and MLL4, PR-DUB and MiDAC complexes. Interestingly, one of the novel UTX isoforms, which lacks exons 14 and 16, fails to interact with PR-DUB and MiDAC complex members. In conclusion, UTX mRNAs undergo extensive alternative splicing, which controls the subcellular localization of UTX and its interactions with other chromatin regulatory complexes.

Introducing a simple and cost-effective RT-PCR protocol for detection of DPYD*2A polymorphism: the first study in Kurdish population.

PURPOSE: Fluoropyrimidines, the major chemotherapeutic agents in various malignancies treatment, are metabolized by dihydropyrimidine dehydrogenase (DPD). DPD deficiency can lead to severe and sometimes fatal toxicity. In the present study, we developed a simple protocol to detect the DPYD*2A variant. Common side effects in patients treated with these drugs were also evaluated in a Kurdish population. METHOD: We established a reverse-transcriptase polymerase chain reaction (RT-PCR) technique for detection of DPYD*2A. Sanger sequencing was used to confirm the results. 121 Kurdish patients receiving fluoropyrimidine derivatives were enrolled, and clinical information regarding the dosage and toxicity was analyzed. RESULTS: Our RT-PCR method was able to detect one patient with heterozygous state for DPYD*2A (0.8%). The most observed adverse drug reactions were tingling, nausea, and hair loss. The frequency of patients with the toxicity of grade 3 or worse was 6.6%. CONCLUSION: This was the first study that detect DPYD*2A polymorphism in the Kurdish population. Our method was successfully able to detect the DPYD*2A variant and, due to its simplicity and cost-effectiveness, it may be considered as an alternative to the current methods, especially in developing countries. Our detected polymorphism rate at 0.8% is comparable with other studies. Despite the low rate of DPYD*2A polymorphism, pharmacogenetics assessment before beginning the treatment process is highly recommended due to its association with a high risk of severe toxicity.

Telomerase activation in small intestinal neuroendocrine tumours is associated with aberrant TERT promoter methylation, but not hot-spot mutations.

Telomere maintenance is a critical requirement for enabling replicative immortality and tumour development. Here, telomerase expression and activity, telomere length (TL) and potential regulatory factors that can underlie telomerase machinery alterations in small intestinal neuroendocrine tumours (SI-NETs) were analyzed. Telomerase activity assessed by TRAP assay was increased in SI-NETs compared to normal ileum (P < 0.001). The telomerase reverse transcriptase gene (TERT) was over-expressed in SI-NETs vs. normal ileal samples (P = 0.01). Furthermore, relative TL assessed by qPCR was found shorter in tumours compared with normal ileum (P = 0.02) and in distant metastasis samples compared to primary tumours and local metastases (P= 0.02). TERT promoter hotspot mutations were not present and TERT copy number gain was only observed in 3/70 tumour samples. TERT or chromosome 18 copy number alterations were not associated with telomerase expression and activity or TL. However, hypermethylation of TERT promoter in Region B - in the proximity of the transcription start site - was inversely correlated with TERT expression and telomerase activity and positively correlated with TL. Global LINE1 methylation was positively correlated with TERT promoter Region B methylation and was inversely correlated with telomerase activity, TERT expression and the upstream Region A methylation. The results show that telomerase activation, TERT expression and shorter telomeres are commonly found in SI-NETs. Aberrant DNA methylation of TERT promoter and of LINE1 can be implicated in abnormal regulation of TERT in SI-NETs.

Proteomics identifies neddylation as a potential therapy target in small intestinal neuroendocrine tumors.

Patients with small intestinal neuroendocrine tumors (SI-NETs) frequently develop spread disease; however, the underlying molecular mechanisms of disease progression are not known and effective preventive treatment strategies are lacking. Here, protein expression profiling was performed by HiRIEF-LC-MS in 14 primary SI-NETs from patients with and without liver metastases detected at the time of surgery and initial treatment. Among differentially expressed proteins, overexpression of the ubiquitin-like protein NEDD8 was identified in samples from patients with liver metastasis. Further, NEDD8 correlation analysis indicated co-expression with RBX1, a key component in cullin-RING ubiquitin ligases (CRLs). In vitro inhibition of neddylation with the therapeutic agent pevonedistat (MLN4924) resulted in a dramatic decrease of proliferation in SI-NET cell lines. Subsequent mass spectrometry-based proteomics analysis of pevonedistat effects and effects of the proteasome inhibitor bortezomib revealed stabilization of multiple targets of CRLs including p27, an established tumor suppressor in SI-NET. Silencing of NEDD8 and RBX1 using siRNA resulted in a stabilization of p27, suggesting that the cellular levels of NEDD8 and RBX1 affect CRL activity. Inhibition of CRL activity, by either NEDD8/RBX1 silencing or pevonedistat treatment of cells resulted in induction of apoptosis that could be partially rescued by siRNA-based silencing of p27. Differential expression of both p27 and NEDD8 was confirmed in a second cohort of SI-NET using immunohistochemistry. Collectively, these findings suggest a role for CRLs and the ubiquitin proteasome system in suppression of p27 in SI-NET, and inhibition of neddylation as a putative therapeutic strategy in SI-NET.

Molecular profiles of oxyphilic and chief cell parathyroid adenoma.

CONTEXT: Parathyroid adenomas may be composed of chief cells (conventional or water-clear), oxyphilic cells or a mixture of both cells. The molecular background is rarely studied. OBJECTIVE: To molecularly characterize parathyroid adenomas of different cell type composition. DESIGN: Chief and oxyphilic cell adenomas were compared in a cohort of 664 sporadic cases. Extensive analyses of parathyroid tissues were performed in subgroup. Gene expressions of known parathyroid-related genes were quantified by qRT-PCR. Protein expression profiles determined by liquid chromatography - tandem mass spectrometry (LC-MS/MS) were compared between each type of parathyroid adenomas. Selected proteins were analysed by Western blot and immunohistochemistry. RESULTS: Patients with oxyphilic cell adenoma were found to be older at the time of operation than chief cell adenoma cases but did not differ in gender, serum calcium or tumor weight. The gene expression of CASR, VDR, FGFR1, CYP27B1, CYP24A1, PTHLH, GCM2, NDUFA13, CDKN1B, MEN1 and CNND1 did not differ between the groups. VDR protein levels were weaker in oxyphilic adenomas. The proteomic studies identified a set of novel dysregulated proteins of interest such as nuclear receptor subfamily 2 group C member 2 (TR4), LIM domain only protein 3 (LMO3) and calcium-binding protein B (S100B). LMO3 and S100B showed higher expression in oxyphilic adenoma and may be involve in parathyroid tumorgenesis through the p53 pathway. TR4 showed different subcellular localisation between adenoma and normal rim. CONCLUSION: Chief and oxyphilic cell parathyroid adenomas have partly overlapping but also distinct molecular profiles. The calmodulin-eEF2K, TR4 and p53 pathways may be involved in the tumor development.

TERT promoter hypermethylation is associated with poor prognosis in adrenocortical carcinoma.

Telomere maintenance, most commonly achieved by telomerase activation through induction of the telomerase reverse transcriptase (TERT) gene, is required for cell immortalization, a hallmark of cancer. Adrenocortical carcinoma (ACC) is an endocrine tumor for which TERT promoter mutations and telomerase activation have been reported. The present study assessed alterations of the TERT gene locus and telomere length in relation to clinical characteristics in ACC. In total, 38 cases of ACC with known TERT promoter mutational status were included. TERT promoter methylation densities were assessed by pyrosequencing, and TERT copy numbers and telomere length were determined by quantitative polymerase chain reaction analysis, followed by comparison of the mRNA expression of TERT and clinical parameters. The ACC tissue samples showed increased TERT copy numbers, compared with normal adrenal tissue (NAT) samples (P=0.001). Mutually exclusive TERT copy number gains or promoter mutation were present in 70% of the ACC samples. The ACC tissues exhibited higher levels of CpG promoter methylation of all eight CpG sites investigated within the ­578 to ­541 bp (Region A), compared with the NATs (P=0.001). High methylation density at this region was associated with metastatic disease and/or relapse, poor survival rates and higher European Network for the Study of Adrenal Tumor stage (P<0.05). The mRNA expression of TERT was inversely correlated with methylation density at ­162 to ­100 bp (Region B). Correlation was observed between relative telomere length and the gene expression of TERT. It was concluded that epigenetic alterations of the TERT promoter are frequent and associated with advanced disease and poorer clinical outcome in ACC.

Loss of miR-514a-3p regulation of PEG3 activates the NF-kappa B pathway in human testicular germ cell tumors.

Deregulation of microRNAs (miRNAs) contributes to the development and progression of many cancer types; however, their functions in the pathogenesis of testicular germ cell tumor (TGCT) remain unclear. Here, we determined miRNA expression profiles of TGCTs and normal testes using small RNA sequencing, and identified several deregulated miRNAs in TGCTs, including the miR-506~514 cluster. In functional studies in vitro we demonstrated that miR-514a-3p induced apoptosis through direct regulation of the paternally expressed gene 3 (PEG3), and ectopically expressed PEG3 could rescue the apoptotic effect of miR-514a-3p overexpression. Silencing of PEG3 or miR-514a-3p overexpression reduced nuclear accumulation of p50 and NF-κB reporter activity. Furthermore, PEG3 was co-immunoprecipitated with tumor necrosis factor receptor-associated factor 2 (TRAF2) in TGCT cell lysates. We propose a model of PEG3-mediated activation of NF-κB in TGCT. Loss of miR-514a-3p expression in TGCT increases PEG3 expression that recruits TRAF2 and activates the NF-kappa B pathway, which protects germ cells from apoptosis. Importantly, we observed strong expression of PEG3 and nuclear p50 in the majority of TGCTs (83% and 78%, respectively). In conclusion, our study describes a novel function for miR-514a-3p in TGCT and highlights an unrecognized mechanism of PEG3 regulation and NF-κB activation in TGCT.

Human papillomavirus and its clinical relevance in oesophageal squamous cell carcinoma in a Kurdish population in the west of Iran.

Background The aetiological role of Human Papillomavirus (HPV) in oesophageal squamous cell carcinoma (ESCC) was evaluated by assessment of the presence and status of HPV DNA in a Kurdish population in the west of Iran. Methods One hundred and three paraffin-embedded ESCC tissue samples, diagnosed between 2007-2013, were included in the study. DNA was extracted and then HPV presence and genotypes were determined by PCR and INNO-LiPA genotyping, respectively. Results HPV DNA was detected in 11/103 (10.7%) of ESCCs. HPV-18 and HPV-16 genotypes were determined in five and six samples, respectively. Co-infection of HPV-6 was only found with HPV-18 in two cases. There were no statistically significant distinctions between HPV-positive and HPV-negative cases with regard to clinical and pathologic findings. Conclusion The present study indicates that, among a group of Kurdish people in two provinces in the west of Iran, as a low-risk ESCC area, HPV could be one of the risk factors, although in a small proportion of the patients.

Genetic and epigenetic background and protein expression profiles in relation to telomerase activation in medullary thyroid carcinoma.

Medullary thyroid carcinomas (MTCs) exhibit telomerase activation in strong association with shorter patient survival. To understand the background of telomerase activation we quantified TERT copy numbers and TERT promoter methylation in 42 MTCs and normal thyroid references. Gain of TERT was demonstrated by quantitative PCR in 5/39 sporadic MTC. Increased methylation index (MetI) for CpG methylation at the TERT promoter was found in sporadic MTCs (P < 0.0001) and in MEN 2 associated MTCs (P = 0.011) vs. normal thyroid tissues. MetI correlated positively with TERT gene expression (r = 0.432, P = 0.006) and negatively with telomere length (r = -0.343, P = 0.032). MTC cases with MetI above the median of 52% had shorter survival as compared to cases with lower MetI (P = 0.005 for overall survival and P = 0.007 for disease-related survival).Protein expression profiles obtained by mass spectrometry were then studied in relation to telomerase activation in MTCs. Comparing protein levels between tumors defined by telomerase activity status, 240 proteins were associated with telomerase activity. Among telomerase activation positive cases a set of proteins was found to discriminate between MTCs with high and low TERT gene expression with enrichment for proteins involved in telomerase regulation. XRCC5 mRNA expression was found increased in MTCs vs. normal thyroid (P = 0.007). In conclusion the findings suggest a role for TERT copy number gain, TERT promoter methylation and XRCC5 expression in telomerase activation and telomere maintenance of MTC.

Proteomics Suggests a Role for APC-Survivin in Response to Somatostatin Analog Treatment of Neuroendocrine Tumors.

CONTEXT: Somatostatin analogs are established in the treatment of neuroendocrine tumors (NETs) including small intestinal NET; however, the molecular mechanisms are not well known. Here, we examined the direct effects of lanreotide in NET cell line models. SETTING AND DESIGN: The cell lines HC45 and H727 were treated with 10nM lanreotide for different time periods and alterations of the proteome were analyzed by in-depth high-resolution isoelectric focusing tandem liquid chromatography-mass spectrometry. We next investigated whether the observed suppression of survivin was mediated by adenomatous polyposis coli (APC) and possible effects on tumor proliferation in vitro. Expression of survivin was assessed by immunohistochemistry in 112 NET cases and compared with patient outcome. RESULTS: We quantified 6451 and 7801 proteins in HC45 and H727, respectively. After short time lanreotide treatment APC was increased and survivin reduced. Overexpression of APC in H727 cells decreased, and APC knock-down elevated the survivin level. The lanreotide regulation of APC-survivin could be suppressed by small interfering RNA against somatostatin receptor 2. Although lanreotide only gave slight inhibition of proliferation, targeting of survivin with the small molecule YM155 dramatically reduced proliferation. Moderate or high as compared with low or absent total survivin expression was associated with shorter progression-free survival, independent of tumor stage, grade, and localization. CONCLUSIONS: We report a proteome-wide analysis of changes in response to lanreotide in NET cell lines. This analysis suggests a connection between somatostatin analog, APC, and survivin levels. Survivin is a possible prognostic factor and a new potential therapeutic target in NETs.

Global hypomethylation and promoter methylation in small intestinal neuroendocrine tumors: an in vivo and in vitro study.

Aberrant DNA methylation is a feature of human cancer affecting gene expression and tumor phenotype. Here, we quantified promoter methylation of candidate genes and global methylation in 44 small intestinal-neuroendocrine tumors (SI-NETs) from 33 patients by pyrosequencing. Findings were compared with gene expression, patient outcome and known tumor copy number alterations. Promoter methylation was observed for WIF1, RASSF1A, CTNNB1, CXCL14, NKX2-3, P16, LAMA1, and CDH1. By contrast APC, CDH3, HIC1, P14, SMAD2, and SMAD4 only had low levels of methylation. WIF1 methylation was significantly increased (P = 0.001) and WIF1 expression was reduced in SI-NETs vs. normal references (P = 0.003). WIF1, NKX2-3, and CXCL14 expression was reduced in metastases vs. primary tumors (P<0.02). Low expression of RASSF1A and P16 were associated with poor overall survival (P = 0.045 and P = 0.011, respectively). Global methylation determined by pyrosequencing of LINE1 repeats was reduced in tumors vs. normal references, and was associated with loss in chromosome 18. The tumors fell into three clusters with enrichment of WIF1 methylation and LINE1 hypomethylation in Cluster I and RASSF1A and CTNNB1 methylation and loss in 16q in Cluster II. In Cluster III, these alterations were low-abundant and NKX2-3 methylation was low. Similar analyses in the SI-NET cell lines HC45 and CNDT2 showed methylation for CDH1 and WIF1 and/or P16, CXCL14, NKX2-3, LAMA1, and CTNNB1. Treatment with the demethylating agent 5-azacytidine reduced DNA methylation and increased expression of these genes in vitro. In conclusion, promoter methylation of tumor suppressor genes is associated with suppressed gene expression and DNA copy number alterations in SI-NETs, and may be restored in vitro.

Global and gene-specific promoter methylation analysis in primary hyperparathyroidism.

Epigenetic mechanisms involved in primary hyperparathyroidism are poorly understood as studies are limited. In order to understand the role of aberrant DNA promoter methylation in the pathogenesis of parathyroid tumors, we have quantified the CpG island promoter methylation density of several candidate genes including APC (promoter 1A and 1B), ß-catenin (CTNNB1), CASR, CDC73/HRPT2, MEN1, P16 (CDKN2A), PAX1, RASSF1A, SFRP1 and VDR in 72 parathyroid tumors and 3 normal parathyroid references using bisulfite pyrosequencing. Global methylation levels were assessed for LINE-1. We also compared methylation levels with gene expression levels measured by qRT-PCR for genes showing frequent hypermethylation. The adenomas displayed frequent hypermethylation of APC 1A (37/66; 56%), RASSF1A (34/66; 52%) and ß-catenin (19/66; 29%). One of the three atypical adenomas was hypermethylated for APC 1A. The three carcinomas were hypermethylated for RASSF1A and SFRP1, and the latter was only observed in this subtype. The global methylation density was similar in tumors (mean 70%) and parathyroid reference samples (mean 70%). In general, hypermethylated genes had reduced expression in the parathyroid adenomas using qRT-PCR. Among the adenomas, methylation of APC 1A correlated with adenoma weight (r = 0.306, p < 0.05). Furthermore, the methylation status of RASSF1A correlated with each of APC 1A (r = 0.289, p < 0.05) and ß-catenin (r = 0.315, p < 0.01). Our findings suggest a role for aberrant DNA promoter methylation of APC 1A, ß-catenin and RASSF1A in a subset of parathyroid tumors.