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1.  Estrogen receptor and HER2/neu status affect epigenetic differences of tumor-related genes in primary breast tumors 
Estrogen receptor (ER)-positive breast cancers are considered prognostically more favorable than ER-negative tumors, whereas human epidermal growth factor receptor (HER)2/neu-positive breast cancers are associated with worse prognosis. The objective of the present study was to determine whether ER-positive and ER-negative status relates to epigenetic changes in breast cancer-related genes. To evaluate epigenetic differences in tumor-related genes relating to ER and HER2/neu status of primary tumors, we examined the promoter methylation status of the promoter region CpG islands of eight major breast tumor-related genes (RASSF1A, CCND2, GSPT1, TWIST, APC, NES1, RARβ2, and CDH1).
Paired ER-positive (n = 65) and ER-negative (n = 65) primary breast tumors (n = 130) matched for prognostic factors were assessed. DNA was extracted from paraffin-embedded tumor tissue after microdissection, and methylation-specific PCR and capillary-array electrophoresis analysis were performed.
In early stages of tumor progression (T1 and N0), RASSF1A and CCND2 were significantly (P < 0.05) more methylated in ER-positive than in ER-negative tumors. GSTP1 hypermethylation was more frequent in the lymph node metastasis positive group than in the negative group. Double negative (ER-negative, HER2/neu-negative) breast cancers had significantly lesser frequencies of RASSF1A, GSTP1, and APC methylation (P < 0.0001, P < 0.0001, and P = 0.0035, respectively). Both ER and HER2/neu status correlated independently with these epigenetic alterations.
We demonstrated significant differences in tumor-related gene methylation patterns relevant to ER and HER2/neu status of breast tumors. This may be of significance in the assessment of targeted therapy resistance related to ER and HER2/neu status in breast cancer patients.
PMCID: PMC2481494  PMID: 18485221
2.  Correlation between CpG methylation profiles and hormone receptor status in breast cancers 
Aberrant DNA methylation has been found frequently in human breast cancers, associated with the loss of expression of a number of regulatory genes for growth and correlated to clinical outcomes. The present study was undertaken to determine whether methylation of a set of growth-suppressor genes would correlate to the expression of estrogen receptors (ERs) and progesterone receptors (PRs).
We used a pyrosequencing methylation analysis to study the methylation of 12 known growth-suppressor genes in 90 pairs of malignant/normal breast tissues. We also examined the expression of ERs and PRs in those specimens by immunohistochemistry. Mutations of p53 in tumor cells were detected by direct sequencing.
Twelve tumor-suppressor genes: ARHI, RASSF1A, HIN-1, RARβ2, hMLH1, 14-3-3 σ, RIZ1, p16, E-cadherin, RIL, CDH13, and NKD2 were selected for this methylation study. Five of them (RIL, HIN-1, RASSF1A, CDH13, and RARβ2) were frequently methylated in breast cancers (57%, 49%, 58%, 44%, and 17%, respectively) but not the normal breast (0–4%). Two panels of methylation profiles were defined. The methylation of the HIN-1/RASSFIA panel strongly correlated to the expression of ERs, PRs, and hormone receptors (HRs; which were defined as 'positive' if ERs and/or PRs were positive; p < 0.001). Conversely, the methylation of the RIL/CDH13 panel strongly correlated to negative ER, PR, and HR expression (p = 0.001, 0.025, and 0.001, respectively). The subset of triple-negative breast cancers (in other words, those with negative ER, PR, and HER-2/neu status) was positively associated with the methylation of the RIL/CDH13 panel and negatively associated with the HIN-1/RASSF1A panel. Mutations of p53 were found in nine breast tumors (11%), seven of which lacked methylation in both panels.
We have defined two panels (HIN-1/RASSFIA, and RIL/CDH13) of methylation profiles, which correlated, either positively or negatively, to HR status.
PMCID: PMC2206733  PMID: 17764565
3.  Methylation profiling of twenty promoter-CpG islands of genes which may contribute to hepatocellular carcinogenesis 
BMC Cancer  2002;2:29.
Hepatocellular carcinoma (HCC) presents one of the major health threats in China today. A better understanding of the molecular genetics underlying malignant transformation of hepatocytes is critical to success in the battle against this disease. The methylation state of C5 of the cytosine in the CpG di-nucleotide that is enriched within or near the promoter region of over 50 % of the polymerase II genes has a drastic effect on transcription of these genes. Changes in the methylation profile of the promoters represent an alternative to genetic lesions as causative factors for the tumor-specific aberrant expression of the genes.
We have used the methylation specific PCR method in conjunction with DNA sequencing to assess the methylation state of the promoter CpG islands of twenty genes. Aberrant expression of these genes have been attributed to the abnormal methylation profile of the corresponding promoter CpG islands in human tumors.
While the following sixteen genes remained the unmethylated in all tumor and normal tissues: CDH1, APAF1, hMLH1, BRCA1, hTERC, VHL, RARβ, TIMP3, DAPK1, SURVIVIN, p14ARF, RB1, p15INK4b, APC, RASSF1c and PTEN, varying degrees of tumor specific hypermethylation were associated with the p16INK4a , RASSF1a, CASP8 and CDH13 genes. For instance, the p16INK4a was highly methylated in HCC (17/29, 58.6%) and less significantly methylated in non-cancerous tissue (4/29. 13.79%). The RASSF1a was fully methylated in all tumor tissues (29/29, 100%), and less frequently methylated in corresponding non-cancerous tissue (24/29, 82.75%).
Furthermore, co-existence of methylated with unmethylated DNA in some cases suggested that both genetic and epigenetic (CpG methylation) mechanisms may act in concert to inactivate the p16INK4a and RASSF1a in HCC. Finally, we found a significant association of cirrhosis with hypermethylation of the p16INK4a and hypomethylation of the CDH13 genes. For the first time, the survey was carried out on such an extent that it would not only provide new insights into the molecular mechanisms underscoring the aberrant expression of the genes in this study in HCC, but also offer essential information required for a good methylation-based diagnosis of HCC.
PMCID: PMC139988  PMID: 12433278
4.  Aberrant Methylation of Multiple Tumor Suppressor Genes in Aging Liver, Chronic Hepatitis, and Hepatocellular Carcinoma 
Hepatology (Baltimore, Md.)  2008;47(3):908-918.
Aberrant DNA methylation is an important epigenetic alteration in hepatocellular carcinoma (HCC). However, the molecular processes underlying the methylator phenotype and the contribution of hepatitis viruses are poorly understood. The current study is a comprehensive methylation analysis of human liver tissue specimens. A total of 176 liver tissues, including 77 pairs of HCCs and matching noncancerous liver and 22 normal livers, were analyzed for methylation. Methylation of 19 epigenetic markers was quantified, and the results were correlated with different disease states and the presence or absence of hepatitis B virus (HBV) and hepatitis C virus (HCV) infections. Based on methylation profiles, the 19 loci were categorized into 3 groups. Normal liver tissues showed methylation primarily in group 1 loci (HIC-1, CASP8, GSTP1, SOCS1, RASSF1A, p16, APC), which was significantly higher than group 2 (CDH1, RUNX3, RIZ1, SFRP2, MINT31) and group 3 markers (COX2, MINT1, CACNA1G, RASSF2, MINT2, Reprimo, DCC) (P < 0.0001). Noncancerous livers demonstrated increased methylation in both group 1 and group 2 loci. Methylation was significantly more abundant in HCV-positive livers compared with normal liver tissues. Conversely, HCC showed frequent methylation at each locus investigated in all 3 groups. However, the group 3 loci showed more dense and frequent methylation in HCV-positive cancers compared with both HBV-positive cancers and virus-negative cancers (P < 0.0001).
Methylation in HCC is frequent but occurs in a gene-specific and disease-specific manner. Methylation profiling allowed us to determine that aberrant methylation is commonly present in normal aging livers, and sequentially progresses with advancing stages of chronic viral infection. Finally, our data provide evidence that HCV infection may accelerate the methylation process and suggests a continuum of increasing methylation with persistent viral infection and carcinogenesis in the liver.
PMCID: PMC2865182  PMID: 18161048
5.  Nuclear localisation and epigenetic inactivation of the ras effector/tumour suppressor RASSF2A in multiple human cancers 
Oncogene  2007;27(12):1805-1811.
RASSF2 is a recently identified member of a class of novel tumour suppressor genes, all containing a ras association domain. We previously demonstrated that the A isoform of RASSF2, is frequently inactivated by promoter region hypermethylation in colorectal tumours and adenomas, methylation was tumour specific and that expression in methylated tumour lines could be reactivated by treatment with 5-aza-2dc. RASSF2 resides at 20p13, this region has been demonstrated to be frequently lost in human cancers. In this report we investigated methylation status of the RASSF2A promoter CpG island in a series of breast, ovarian and non-small cell lung cancers (NSCLC). RASSF2A was frequently methylated in breast tumour cell lines 65% (13/20) and in primary breast tumours 38% (15/40). RASSF2A gene expression could be switched back on in methylated breast tumour cell lines after treatment with 5-aza-2dC, whilst unmethylated lines showed no difference in level of expression before and after 5-aza-2dC treatment. RASSF2A was also frequently methylated in NSCLC tumours 44% (22/50). Methylation in breast tumours and NSCLC was tumour specific. We did not detect RASSF2A methylation in ovarian tumours (0/17). Furthermore no mutations were found in the coding region of RASSF2A in these ovarian tumours.
RASSF2A suppressed breast tumour cell growth in vitro (through colony formation and soft agar assays) and in vivo. We identified a highly conserved putative bipartite nuclear localisation signal (NLS) between amino acids 151 and 167 in the RASSF2A sequence and demonstrated that endogenous RASSF2A localised to the nucleus. Mutation of the putative nuclear localisation signal abolished the nuclear localisation so RASSF2A became predominantly cytoplasmic. Our data indicates that RASSF2A is frequently methylated in colorectal, breast and NSCLC tumours, furthermore, the methylation is tumour specific. Hence we have identified RASSF2A as a novel methylation marker for multiple malignancies and it has the potential to be developed into a valuable marker for screening several cancers in parallel using promoter hypermethylation profiles.
We also demonstrate that RASSF2 has a functional NLS signal. Furthermore this is the first report demonstrating that RASSF2 suppresses growth of cancer cells in vivo. Hence providing further evidence for its role as a tumour suppressor gene located at 20p13.
PMCID: PMC2948550  PMID: 17891178
6.  Methylation of HIN-1, RASSF1A, RIL and CDH13 in breast cancer is associated with clinical characteristics, but only RASSF1A methylation is associated with outcome 
BMC Cancer  2012;12:243.
Aberrant promoter CpG island hypermethylation is associated with transcriptional silencing. Tumor suppressor genes are the key targets of hypermethylation in breast cancer and therefore may lead to malignancy by deregulation of cell growth and division. Our previous pilot study with pairs of malignant and normal breast tissues identified correlated methylation of two pairs of genes - HIN-1/RASSFIA and RIL/CDH13 - with expression of estrogen receptors (ER), progesterone receptors (PR), and HER2 (HER2). To determine the impact of methylation on clinical outcome, we have conducted a larger study with breast cancers for which time to first recurrence and overall survival are known.
Tumors from 193 patients with early stage breast cancer who received no adjuvant systemic therapy were used to analyze methylation levels of RIL, HIN-1, RASSF1A and CDH13 genes for associations with known predictive and prognostic factors and for impact on time to first recurrence and overall survival.
In this study, we found that ER was associated with RASSF1A methylation (p < 0.001) and HIN-1 methylation (p = 0.002). PR was associated with RIL methylation (p = 0.012), HIN-1 (p = 0.002), and RASSF1A methylation (p = 0.019). Tumor size was associated with RIL and CDH13 methylation (both p = 0.002), and S-phase was associated with RIL methylation (p = 0.036). Only RASSF1A was associated with worse time to first recurrence (p = 0.045) and worse overall survival (p = 0.016) after adjusting for age, tumor size, S-phase, estrogen receptor and progesterone receptor.
Methylation of HIN-1, RASSF1A, RIL and CDH13 in breast cancers was associated with clinical characteristics, but only RASSF1A methylation was associated with time to first recurrence and overall survival. Our data suggest that RASSF1A methylation could be a potential prognostic biomarker.
PMCID: PMC3476972  PMID: 22695491
7.  The RASSF gene family members RASSF5, RASSF6 and RASSF7 show frequent DNA methylation in neuroblastoma 
Molecular Cancer  2012;11:40.
Hypermethylation of promotor CpG islands is a common mechanism that inactivates tumor suppressor genes in cancer. Genes belonging to the RASSF gene family have frequently been reported as epigenetically silenced by promotor methylation in human cancers. Two members of this gene family, RASSF1A and RASSF5A have been reported as methylated in neuroblastoma. Data from our previously performed genome-wide DNA methylation array analysis indicated that other members of the RASSF gene family are targeted by DNA methylation in neuroblastoma.
In the current study, we found that several of the RASSF family genes (RASSF2, RASSF4, RASSF5, RASSF6, RASSF7, and RASSF10) to various degrees were methylated in neuroblastoma cell lines and primary tumors. In addition, several of the RASSF family genes showed low or absent mRNA expression in neuroblastoma cell lines. RASSF5 and RASSF6 were to various degrees methylated in a large portion of neuroblastoma tumors and RASSF7 was heavily methylated in most tumors. Further, CpG methylation sites in the CpG islands of some RASSF family members could be used to significantly discriminate between biological subgroups of neuroblastoma tumors. For example, RASSF5 methylation highly correlated to MYCN amplification and INRG stage M. Furthermore, high methylation of RASSF6 was correlated to unfavorable outcome, 1p deletion and MYCN amplification in our tumor material.
In conclusion
This study shows that several genes belonging to the RASSF gene family are methylated in neuroblastoma. The genes RASSF5, RASSF6 and RASSF7 stand out as the most promising candidate genes for further investigations in neuroblastoma.
PMCID: PMC3493266  PMID: 22695170
8.  Cytoplasmic RASSF2A is a proapoptotic mediator whose expression is epigenetically silenced in gastric cancer 
Carcinogenesis  2008;29(7):1312-1318.
Gastric cancer cells often show altered Ras signaling, though the underlying molecular mechanism is not fully understood. We examined the expression profile of eight ras-association domain family (RASSF) genes plus MST1/2 and found that RASSF2A is the most frequently downregulated in gastric cancer. RASSF2A was completely silenced in 6 of 10 gastric cancer cell lines as a result of promoter methylation, and expression was restored by treating the cells with 5-aza-2′-deoxycytidine. Introduction of RASSF2A into non-expressing cell lines suppressed colony formation and induced apoptosis. These effects were associated with the cytoplasmic localization of RASSF2A and morphological changes to the cells. Complementary DNA microarray analysis revealed that RASSF2A suppresses the expression of inflammatory cytokines, which may in turn suppress angiogenesis and invasion. In primary gastric cancers, aberrant methylation of RASSF2A was detected in 23 of 78 (29.5%) cases, and methylation correlated significantly with an absence of the lymphatic invasion, absence of venous invasion, absence of lymph node metastasis, less advanced stages, Epstein–Barr virus, absence of p53 mutations and the presence of the CpG island methylator phenotype-high. These results suggest that epigenetic inactivation of RASSF2A is required for tumorigenesis in a subset of gastric cancers.
PMCID: PMC2500213  PMID: 18310659
9.  MicroRNA expression in ovarian carcinoma and its correlation with clinicopathological features 
MicroRNA (miRNA) expression is known to be deregulated in ovarian carcinomas. However, limited data is available about the miRNA expression pattern for the benign or borderline ovarian tumors as well as differential miRNA expression pattern associated with histological types, grades or clinical stages in ovarian carcinomas. We defined patterns of microRNA expression in tissues from normal, benign, borderline, and malignant ovarian tumors and explored the relationship between frequently deregulated miRNAs and clinicopathologic findings, response to therapy, survival, and association with Her-2/neu status in ovarian carcinomas.
We measured the expression of nine miRNAs (miR-181d, miR-30a-3p, miR-30c, miR-30d, miR-30e-3p, miR-368, miR-370, miR-493-5p, miR-532-5p) in 171 formalin-fixed, paraffin-embedded ovarian tissue blocks as well as six normal human ovarian surface epithelial (HOSE) cell lines using Taqman-based real-time PCR assays. Her-2/neu overexpression was assessed in ovarian carcinomas (n = 109 cases) by immunohistochemistry analysis.
Expression of four miRNAs (miR-30c, miR-30d, miR-30e-3p, miR-370) was significantly different between carcinomas and benign ovarian tissues as well as between carcinoma and borderline tissues. An additional three miRNAs (miR-181d, miR-30a-3p, miR-532-5p) were significantly different between borderline and carcinoma tissues. Expression of miR-532-5p was significantly lower in borderline than in benign tissues. Among ovarian carcinomas, expression of four miRNAs (miR-30a-3p, miR-30c, miR-30d, miR-30e-3p) was lowest in mucinous and highest in clear cell samples. Expression of miR-30a-3p was higher in well-differentiated compared to poorly differentiated tumors (P = 0.02), and expression of miR-370 was higher in stage I/II compared to stage III/IV samples (P = 0.03). In multivariate analyses, higher expression of miR-181d, miR-30c, miR-30d, and miR-30e-3p was associated with significantly better disease-free or overall survival. Finally, lower expression of miR-30c, miR-30d, miR-30e-3p and miR-532-5p was significantly associated with overexpression of Her-2/neu.
Aberrant expression of miRNAs is common in ovarian tumor suggesting involvement of miRNA in ovarian tumorigenesis. They are associated with histology, clinical stage, survival and oncogene expression in ovarian carcinoma.
PMCID: PMC3449188  PMID: 22925189
miRNA; Ovarian tumor; Her2/neu; Survival
10.  Epigenetic silencing of RASSF1A deregulates cytoskeleton and promotes malignant behavior of adrenocortical carcinoma 
Molecular Cancer  2013;12:87.
Adrenocortical carcinoma (ACC) is a rare endocrine malignancy with high mutational heterogeneity and a generally poor clinical outcome. Despite implicated roles of deregulated TP53, IGF-2 and Wnt signaling pathways, a clear genetic association or unique mutational link to the disease is still missing. Recent studies suggest a crucial role for epigenetic modifications in the genesis and/or progression of ACC. This study specifically evaluates the potential role of epigenetic silencing of RASSF1A, the most commonly silenced tumor suppressor gene, in adrenocortical malignancy.
Using adrenocortical tumor and normal tissue specimens, we show a significant reduction in expression of RASSF1A mRNA and protein in ACC. Methylation-sensitive and -dependent restriction enzyme based PCR assays revealed significant DNA hypermethylation of the RASSF1A promoter, suggesting an epigenetic mechanism for RASSF1A silencing in ACC. Conversely, the RASSF1A promoter methylation profile in benign adrenocortical adenomas (ACAs) was found to be very similar to that found in normal adrenal cortex. Enforced expression of ectopic RASSF1A in the SW-13 ACC cell line reduced the overall malignant behavior of the cells, which included impairment of invasion through the basement membrane, cell motility, and solitary cell survival and growth. On the other hand, expression of RASSF1A/A133S, a loss-of-function mutant form of RASSF1A, failed to elicit similar malignancy-suppressing responses in ACC cells. Moreover, association of RASSF1A with the cytoskeleton in RASSF1A-expressing ACC cells and normal adrenal cortex suggests a role for RASSF1A in modulating microtubule dynamics in the adrenal cortex, and thereby potentially blocking malignant progression.
Downregulation of RASSF1A via promoter hypermethylation may play a role in the malignant progression of adrenocortical carcinoma possibly by abrogating differentiation-promoting RASSF1A- microtubule interactions.
PMCID: PMC3750604  PMID: 23915220
Adrenal cortex; Carcinoma; Adenoma; RASSF1A; Hypermethylation; Epigenetic silencing; Cytoskeleton
11.  Quantitative DNA methylation analyses reveal stage dependent DNA methylation and association to clinico-pathological factors in breast tumors 
BMC Cancer  2013;13:456.
Aberrant DNA methylation of regulatory genes has frequently been found in human breast cancers and correlated to clinical outcome. In the present study we investigate stage specific changes in the DNA methylation patterns in order to identify valuable markers to understand how these changes affect breast cancer progression.
Quantitative DNA methylation analyses of 12 candidate genes ABCB1, BRCCA1, CDKN2A, ESR1, GSTP1, IGF2, MGMT, HMLH1, PPP2R2B, PTEN, RASSF1A and FOXC1 was performed by pyrosequencing a series of 238 breast cancer tissue samples from DCIS to invasive tumors stage I to IV.
Significant differences in methylation levels between the DCIS and invasive stage II tumors were observed for six genes RASSF1A, CDKN2A, MGMT, ABCB1, GSTP1 and FOXC1. RASSF1A, ABCB1 and GSTP1 showed significantly higher methylation levels in late stage compared to the early stage breast carcinoma. Z-score analysis revealed significantly lower methylation levels in DCIS and stage I tumors compared with stage II, III and IV tumors. Methylation levels of PTEN, PPP2R2B, FOXC1, ABCB1 and BRCA1 were lower in tumors harboring TP53 mutations then in tumors with wild type TP53. Z-score analysis showed that TP53 mutated tumors had significantly lower overall methylation levels compared to tumors with wild type TP53. Methylation levels of RASSF1A, PPP2R2B, GSTP1 and FOXC1 were higher in ER positive vs. ER negative tumors and methylation levels of PTEN and CDKN2A were higher in HER2 positive vs. HER2 negative tumors. Z-score analysis also showed that HER2 positive tumors had significantly higher z-scores of methylation compared to the HER2 negative tumors. Univariate survival analysis identifies methylation status of PPP2R2B as significant predictor of overall survival and breast cancer specific survival.
In the present study we report that the level of aberrant DNA methylation is higher in late stage compared with early stage of invasive breast cancers and DCIS for genes mentioned above.
PMCID: PMC3819713  PMID: 24093668
Breast cancer; DNA methylation; Methylation index; Stage; TP53
12.  The RASSF1A Isoform of RASSF1 Promotes Microtubule Stability and Suppresses Tumorigenesis 
Molecular and Cellular Biology  2005;25(18):8356-8367.
The RASSF1A isoform of RASSF1 is frequently inactivated by epigenetic alterations in human cancers, but it remains unclear if and how it acts as a tumor suppressor. RASSF1A overexpression reduces in vitro colony formation and the tumorigenicity of cancer cell lines in vivo. Conversely, RASSF1A knockdown causes multiple mitotic defects that may promote genomic instability. Here, we have used a genetic approach to address the function of RASSF1A as a tumor suppressor in vivo by targeted deletion of Rassf1A in the mouse. Rassf1A null mice were viable and fertile and displayed no pathological abnormalities. Rassf1A null embryonic fibroblasts displayed an increased sensitivity to microtubule depolymerizing agents. No overtly altered cell cycle parameters or aberrations in centrosome number were detected in Rassf1A null fibroblasts. Rassf1A null fibroblasts did not show increased sensitivity to microtubule poisons or DNA-damaging agents and showed no evidence of gross genomic instability, suggesting that cellular responses to genotoxins were unaffected. Rassf1A null mice showed an increased incidence of spontaneous tumorigenesis and decreased survival rate compared with wild-type mice. Irradiated Rassf1A null mice also showed increased tumor susceptibility, particularly to tumors associated with the gastrointestinal tract, compared with wild-type mice. Thus, our results demonstrate that Rassf1A acts as a tumor suppressor gene.
PMCID: PMC1234312  PMID: 16135822
13.  Quantitative promoter methylation analysis of multiple cancer-related genes in renal cell tumors 
BMC Cancer  2007;7:133.
Aberrant promoter hypermethylation of cancer-associated genes occurs frequently during carcinogenesis and may serve as a cancer biomarker. In this study we aimed at defining a quantitative gene promoter methylation panel that might identify the most prevalent types of renal cell tumors.
A panel of 18 gene promoters was assessed by quantitative methylation-specific PCR (QMSP) in 85 primarily resected renal tumors representing the four major histologic subtypes (52 clear cell (ccRCC), 13 papillary (pRCC), 10 chromophobe (chRCC), and 10 oncocytomas) and 62 paired normal tissue samples. After genomic DNA isolation and sodium bisulfite modification, methylation levels were determined and correlated with standard clinicopathological parameters.
Significant differences in methylation levels among the four subtypes of renal tumors were found for CDH1 (p = 0.0007), PTGS2 (p = 0.002), and RASSF1A (p = 0.0001). CDH1 hypermethylation levels were significantly higher in ccRCC compared to chRCC and oncocytoma (p = 0.00016 and p = 0.0034, respectively), whereas PTGS2 methylation levels were significantly higher in ccRCC compared to pRCC (p = 0.004). RASSF1A methylation levels were significantly higher in pRCC than in normal tissue (p = 0.035). In pRCC, CDH1 and RASSF1A methylation levels were inversely correlated with tumor stage (p = 0.031) and nuclear grade (p = 0.022), respectively.
The major subtypes of renal epithelial neoplasms display differential aberrant CDH1, PTGS2, and RASSF1A promoter methylation levels. This gene panel might contribute to a more accurate discrimination among common renal tumors, improving preoperative assessment and therapeutic decision-making in patients harboring suspicious renal masses.
PMCID: PMC1940017  PMID: 17645803
14.  Methylation of tumor suppressor genes in ovarian cancer 
Aberrant methylation of gene promoter regions is one of the mechanisms for inactivation of tumor suppressor genes in human malignancies. In this study, the methylation pattern of 24 tumor suppressor genes was analyzed in 75 samples of ovarian cancer using the methylation-specific multiplex ligation-dependent probe amplification (MS-MLPA) assay. Of the 24 tumor suppressor genes examined, aberrant methylation was observed in 17. The three most frequently methylated genes were CDKN2B, CDH13 and RASSF1, followed by ESR1 and MLH1. Methylation frequencies ranged from 1.3% for CDKN2A, RARβ, CASP8, VHL and TP73 to 24% for CDKN2B. The corresponding normal DNA from each patient was also investigated. Methylation was detected in tumors, although not in normal tissues, with the exception of two samples, indicating aberrant methylation in tumors. Clear cell carcinoma samples exhibited a higher frequency of CDKN2B promoter hypermethylation compared to those of other histological types (P=0.05). Our data indicate that methylation of the CDKN2B gene is a frequent event in ovarian carcinogenesis and that analysis of only three genes is sufficient to detect the presence of methylation in 35% of ovarian cancer cases. However, more studies using a much larger sample size are needed to define the potential role of DNA methylation as a marker for ovarian cancer.
PMCID: PMC3494110  PMID: 23226780
ovarian cancer; methylation; methylation-specific multiplex ligation-dependent probe amplification; tumor suppressor gene
15.  Methylation associated inactivation of RASSF1A and its synergistic effect with activated K-Ras in nasopharyngeal carcinoma 
Epigenetic silencing of tumor suppressor genes associated with promoter methylation is considered to be a hallmark of oncogenesis. RASSF1A is a candidate tumor suppressor gene which was found to be inactivated in many human cancers. Although we have had a prelimilary cognition about the function of RASSF1A, the exact mechanisms about how RASSF1A functions in human cancers were largely unknown. Moreover, the effect of mutated K-Ras gene on the function of RASSF1A is lacking. The aim of this study was to investigate the expression profile and methylation status of RASSF1A gene, and to explore its concrete mechanisms as a tumor suppressor gene in Nasopharyngeal Carcinoma.
We examined the expression profile and methylation status of RASSF1A in two NPC cell lines, 38 primary nasopharyngeal carcinoma and 14 normal nasopharyngeal epithelia using RT-PCR and methylated specific PCR(MSP) respectively. 5-aza-dC was then added to confirm the correlation between hypermethylation status and inactivation of RASSF1A. The NPC cell line CNE-2 was transfected with exogenous pcDNA3.1(+)/RASSF1A plasmid in the presence or absence of mutated K-Ras by liposome-mediated gene transfer method. Flow cytometry was used to examine the effect of RASSF1A on cell cycle modulation and apoptosis. Meanwhile, trypan blue dye exclusion assays was used to detect the effect of RASSF1A transfection alone and the co-transfection of RASSF1A and K-Ras on cell proliferation.
Promoter methylation of RASSF1A could be detected in 71.05% (27/38) of NPC samples, but not in normal nasopharyngeal epithelia. RASSF1A expression in NPC primary tumors was lower than that in normal nasopharyngeal epithelial (p < 0.01). Expression of RASSF1A was down-regulated in two NPC cell lines. Loss of RASSF1A expression was greatly restored by the methyltransferase inhibitor 5-aza-dC in CNE-2. Ectopic expression of RASSF1A in CNE-2 could increase the percentage of G0/G1 phase cells (p < 0.01), inhibit cell proliferation and induce apoptosis (p < 0.001). Moreover, activated K-Ras could enhance the growth inhibition effect induced by RASSF1A in CNE-2 cells (p < 0.01).
Expression of RASSF1A is down-regulated in NPC due to the hypermethylation of promoter. Exogenous expression of RASSF1A is able to induce growth inhibition effect and apoptosis in tumor cell lines, and this effect could be enhanced by activated K-Ras.
PMCID: PMC2809060  PMID: 20042089
16.  The Intronic Long Noncoding RNA ANRASSF1 Recruits PRC2 to the RASSF1A Promoter, Reducing the Expression of RASSF1A and Increasing Cell Proliferation 
PLoS Genetics  2013;9(8):e1003705.
The down-regulation of the tumor-suppressor gene RASSF1A has been shown to increase cell proliferation in several tumors. RASSF1A expression is regulated through epigenetic events involving the polycomb repressive complex 2 (PRC2); however, the molecular mechanisms modulating the recruitment of this epigenetic modifier to the RASSF1 locus remain largely unknown. Here, we identify and characterize ANRASSF1, an endogenous unspliced long noncoding RNA (lncRNA) that is transcribed from the opposite strand on the RASSF1 gene locus in several cell lines and tissues and binds PRC2. ANRASSF1 is transcribed through RNA polymerase II and is 5′-capped and polyadenylated; it exhibits nuclear localization and has a shorter half-life compared with other lncRNAs that bind PRC2. ANRASSF1 endogenous expression is higher in breast and prostate tumor cell lines compared with non-tumor, and an opposite pattern is observed for RASSF1A. ANRASSF1 ectopic overexpression reduces RASSF1A abundance and increases the proliferation of HeLa cells, whereas ANRASSF1 silencing causes the opposite effects. These changes in ANRASSF1 levels do not affect the RASSF1C isoform abundance. ANRASSF1 overexpression causes a marked increase in both PRC2 occupancy and histone H3K27me3 repressive marks, specifically at the RASSF1A promoter region. No effect of ANRASSF1 overexpression was detected on PRC2 occupancy and histone H3K27me3 at the promoter regions of RASSF1C and the four other neighboring genes, including two well-characterized tumor suppressor genes. Additionally, we demonstrated that ANRASSF1 forms an RNA/DNA hybrid and recruits PRC2 to the RASSF1A promoter. Together, these results demonstrate a novel mechanism of epigenetic repression of the RASSF1A tumor suppressor gene involving antisense unspliced lncRNA, in which ANRASSF1 selectively represses the expression of the RASSF1 isoform overlapping the antisense transcript in a location-specific manner. In a broader perspective, our findings suggest that other non-characterized unspliced intronic lncRNAs transcribed in the human genome might contribute to a location-specific epigenetic modulation of genes.
Author Summary
RASSF1A is a tumor suppressor gene whose expression is repressed through epigenetic events in a wide range of different cancers. Repression is effected by DNA hypermethylation of the RASSF1A promoter, which in turn is triggered through histone H3K9/H3K27 trimethylation repressive marks. The addition of the H3K27me3 mark at the RASSF1A promoter locus involves the polycomb repressive complex 2 (PRC2). The molecular mechanisms that control the recruitment of PRC2 to the promoter to initiate H3K27 trimethylation and repress RASSF1A expression have not been described. Here, we identified a long noncoding RNA (lncRNA), termed ANRASSF1 for antisense noncoding RASSF1, that is transcribed from the opposite strand of the RASSF1A gene and is responsible for recruiting PRC2 to the RASSF1A promoter region in a highly location-specific manner. No effect of ANRASSF1 was detected on the promoter of the RASSF1C isoform or the promoters of the four other genes within the vicinity of RASSF1, including two other well-characterized tumor suppressor genes. This work provides evidence that the epigenetic modulation of the tumor suppressor gene RASSF1A is dependent on the lncRNA ANRASSF1 and highlights the importance of further studies on the involvement of ANRASSF1 in tumorigenesis.
PMCID: PMC3749938  PMID: 23990798
17.  DNA methylation patterns in bladder cancer and washing cell sediments: a perspective for tumor recurrence detection 
BMC Cancer  2008;8:238.
Epigenetic alterations are a hallmark of human cancer. In this study, we aimed to investigate whether aberrant DNA methylation of cancer-associated genes is related to urinary bladder cancer recurrence.
A set of 4 genes, including CDH1 (E-cadherin), SFN (stratifin), RARB (retinoic acid receptor, beta) and RASSF1A (Ras association (RalGDS/AF-6) domain family 1), had their methylation patterns evaluated by MSP (Methylation-Specific Polymerase Chain Reaction) analysis in 49 fresh urinary bladder carcinoma tissues (including 14 cases paired with adjacent normal bladder epithelium, 3 squamous cell carcinomas and 2 adenocarcinomas) and 24 cell sediment samples from bladder washings of patients classified as cancer-free by cytological analysis (control group). A third set of samples included 39 archived tumor fragments and 23 matched washouts from 20 urinary bladder cancer patients in post-surgical monitoring. After genomic DNA isolation and sodium bisulfite modification, methylation patterns were determined and correlated with standard clinic-histopathological parameters.
CDH1 and SFN genes were methylated at high frequencies in bladder cancer as well as in paired normal adjacent tissue and exfoliated cells from cancer-free patients. Although no statistically significant differences were found between RARB and RASSF1A methylation and the clinical and histopathological parameters in bladder cancer, a sensitivity of 95% and a specificity of 71% were observed for RARB methylation (Fisher's Exact test (p < 0.0001; OR = 48.89) and, 58% and 17% (p < 0.05; OR = 0.29) for RASSF1A gene, respectively, in relation to the control group.
Indistinct DNA hypermethylation of CDH1 and SFN genes between tumoral and normal urinary bladder samples suggests that these epigenetic features are not suitable biomarkers for urinary bladder cancer. However, RARB and RASSF1A gene methylation appears to be an initial event in urinary bladder carcinogenesis and should be considered as defining a panel of differentially methylated genes in this neoplasia in order to maximize the diagnostic coverage of epigenetic markers, especially in studies aiming at early recurrence detection.
PMCID: PMC2527332  PMID: 18702824
18.  Kras Gene Mutation and RASSF1A, FHIT and MGMT Gene Promoter Hypermethylation: Indicators of Tumor Staging and Metastasis in Adenocarcinomatous Sporadic Colorectal Cancer in Indian Population 
PLoS ONE  2013;8(4):e60142.
Colorectal cancer (CRC) development involves underlying modifications at genetic/epigenetic level. This study evaluated the role of Kras gene mutation and RASSF1A, FHIT and MGMT gene promoter hypermethylation together/independently in sporadic CRC in Indian population and correlation with clinicopathological variables of the disease.
One hundred and twenty four consecutive surgically resected tissues (62 tumor and equal number of normal adjacent controls) of primary sporadic CRC were included and patient details including demographic characteristics, lifestyle/food or drinking habits, clinical and histopathological profiles were recorded. Polymerase chain reaction - Restriction fragment length polymorphism and direct sequencing for Kras gene mutation and Methylation Specific-PCR for RASSF1A, FHIT and MGMT genes was performed.
Kras gene mutation at codon 12 & 13 and methylated RASSF1A, FHIT and MGMT gene was observed in 47%, 19%, 47%, 37% and 47% cases, respectively. Alcohol intake and smoking were significantly associated with presence of Kras mutation (codon 12) and MGMT methylation (p-value <0.049). Tumor stage and metastasis correlated with presence of mutant Kras codon 12 (p-values 0.018, 0.044) and methylated RASSF1A (p-values 0.034, 0.044), FHIT (p-values 0.001, 0.047) and MGMT (p-values 0.018, 0.044) genes. Combinatorial effect of gene mutation/methylation was also observed (p-value <0.025). Overall, tumor stage 3, moderately differentiated tumors, presence of lymphatic invasion and absence of metastasis was more frequently observed in tumors with mutated Kras and/or methylated RASSF1A, FHIT and MGMT genes.
Synergistic interrelationship between these genes in sporadic CRC may be used as diagnostic/prognostic markers in assessing the overall pathological status of CRC.
PMCID: PMC3616004  PMID: 23573237
19.  CpG Island Methylator Phenotype Predicts Progression of Malignant Melanoma 
The CpG island methylator phenotype (CIMP) may be associated with development of malignancy through coordinated inactivation of tumor suppressor and tumor-related genes (TRG) and methylation of multiple noncoding, methylated-in-tumor (MINT) loci. These epigenetic changes create a distinct CIMP pattern that has been linked to recurrence and survival in gastrointestinal cancers. Because epigenetic inactivation of TRGs also has been shown in malignant melanoma, we hypothesized the existence of a clinically significant CIMP in cutaneous melanoma progression.
Experimental Design:
The methylation status of the CpG island promoter region of TRGs related to melanoma pathophysiology (WIF1, TFPI2, RASSF1A, RARβ2, SOCS1, and GATA4) and a panel of MINT loci (MINT1, MINT2, MINT3, MINT12, MINT17, MINT25, and MINT31) in primary and metastatic tumors of different clinical stages (n = 122) was assessed.
Here, we show an increase in hypermethylation of theTRGsWIF1,TFPI2, RASSF1A, and SOCS1with advancing clinical tumor stage. Furthermore, we find a significant positive association between the methylation status of MINT17, MINT31, and TRGs. The methylation status of MINT31is associated with disease outcome in stage III melanoma.
These findings show the significance of a CIMP pattern that is associated with advancing clinical stage of malignant melanoma. Future prospective large-scale studies may determine if CIMP-positive primary melanomas are at high risk of metastasis or recurrence.
PMCID: PMC2703821  PMID: 19223509
20.  Frequent epigenetic inactivation of RASSF2 in thyroid cancer and functional consequences 
Molecular Cancer  2010;9:264.
The Ras association domain family (RASSF) encodes for distinct tumor suppressors and several members are frequently silenced in human cancer. In our study, we analyzed the role of RASSF2, RASSF3, RASSF4, RASSF5A, RASSF5C and RASSF6 and the effectors MST1, MST2 and WW45 in thyroid carcinogenesis.
Frequent methylation of the RASSF2 and RASSF5A CpG island promoters in thyroid tumors was observed. RASSF2 was methylated in 88% of thyroid cancer cell lines and in 63% of primary thyroid carcinomas. RASSF2 methylation was significantly increased in primary thyroid carcinoma compared to normal thyroid, goiter and follicular adenoma (0%, 17% and 0%, respectively; p < 0.05). Patients which were older than 60 years were significantly hypermethylated for RASSF2 in their primary thyroid tumors compared to those younger than 40 years (90% vs. 38%; p < 0.05). RASSF2 promoter hypermethylation correlated with its reduced expression and treatment with a DNA methylation inhibitor reactivated RASSF2 transcription. Over-expression of RASSF2 reduced colony formation of thyroid cancer cells. Functionally our data show that RASSF2 interacts with the proapoptotic kinases MST1 and MST2 and induces apoptosis in thyroid cancer cell lines. Deletion of the MST interaction domain of RASSF2 reduced apoptosis significantly (p < 0.05).
These results suggest that RASSF2 encodes a novel epigenetically inactivated candidate tumor suppressor gene in thyroid carcinogenesis.
PMCID: PMC2956732  PMID: 20920251
21.  Relationship between Tumor DNA Methylation Status and Patient Characteristics in African-American and European-American Women with Breast Cancer 
PLoS ONE  2012;7(5):e37928.
Aberrant DNA methylation is critical for development and progression of breast cancer. We investigated the association of CpG island methylation in candidate genes and clinicopathological features in 65 African-American (AA) and European-American (EA) breast cancer patients. Quantitative methylation analysis was carried out on bisulfite modified genomic DNA and sequencing (pyrosequencing) for promoter CpG islands of p16, ESR1, RASSF1A, RARβ2, CDH13, HIN1, SFRP1 genes and the LINE1 repetitive element using matched paired non-cancerous and breast tumor specimen (32 AA and 33 EA women). Five of the genes, all known tumor suppressor genes (RASSF1A, RARβ2, CDH13, HIN1 and SFRP1), were found to be frequently hypermethylated in breast tumor tissues but not in the adjacent non-cancerous tissues. Significant differences in the CDH13 methylation status were observed by comparing DNA methylation between AA and EA patients, with more obvious CDH13 methylation differences between the two patient groups in the ER- disease and among young patients (age<50). In addition, we observed associations between CDH13, SFRP1, and RASSF1A methylation and breast cancer subtypes and between SFRP1 methylation and patient's age. Furthermore, tumors that received neoadjuvant therapy tended to have reduced RASSF1A methylation when compared with chemotherapy naïve tumors. Finally, Kaplan Meier survival analysis showed a significant association between methylation at 3 loci (RASSF1A, RARβ2 and CDH13) and reduced overall disease survival. In conclusion, the DNA methylation status of breast tumors was found to be significantly associated with clinicopathological features and race/ethnicity of the patients.
PMCID: PMC3365111  PMID: 22701537
22.  Methylation-associated down-regulation of RASSF1A and up-regulation of RASSF1C in pancreatic endocrine tumors 
BMC Cancer  2011;11:351.
RASSF1A gene silencing by DNA methylation has been suggested as a major event in pancreatic endocrine tumor (PET) but RASSF1A expression has never been studied. The RASSF1 locus contains two CpG islands (A and C) and generates seven transcripts (RASSF1A-RASSF1G) by differential promoter usage and alternative splicing.
We studied 20 primary PETs, their matched normal pancreas and three PET cell lines for the (i) methylation status of the RASSF1 CpG islands using methylation-specific PCR and pyrosequencing and (ii) expression of RASSF1 isoforms by quantitative RT-PCR in 13 cases. CpG island A methylation was evaluated by methylation-specific PCR (MSP) and by quantitative methylation-specific PCR (qMSP); pyrosequencing was applied to quantify the methylation of 51 CpGs also encompassing those explored by MSP and qMSP approaches.
MSP detected methylation in 16/20 (80%) PETs and 13/20 (65%) normal pancreas. At qMSP, 11/20 PETs (55%) and 9/20 (45%) normals were methylated in at least 20% of RASSF1A alleles.
Pyrosequencing showed variable distribution and levels of methylation within and among samples, with PETs having average methylation higher than normals in 15/20 (75%) cases (P = 0.01). The evaluation of mRNA expression of RASSF1 variants showed that: i) RASSF1A was always expressed in PET and normal tissues, but it was, on average, expressed 6.8 times less in PET (P = 0.003); ii) RASSF1A methylation inversely correlated with its expression; iii) RASSF1 isoforms were rarely found, except for RASSF1B that was always expressed and RASSF1C whose expression was 11.4 times higher in PET than in normal tissue (P = 0.001). A correlation between RASSF1A expression and gene methylation was found in two of the three PET cell lines, which also showed a significant increase in RASSF1A expression upon demethylating treatment.
RASSF1A gene methylation in PET is higher than normal pancreas in no more than 75% of cases and as such it cannot be considered a marker for this neoplasm. RASSF1A is always expressed in PET and normal pancreas and its levels are inversely correlated with gene methylation. Isoform RASSF1C is overexpressed in PET and the recent demonstration of its involvement in the regulation of the Wnt pathway points to a potential pathogenetic role in tumor development.
PMCID: PMC3170651  PMID: 21838870
23.  DNA methylation in thyroid tumorigenesis 
Cancers  2011;3(2):1732-1743.
Thyroid cancer is the most common endocrine cancer with 1,690 deaths each year. There are four main types of which the papillary and follicular types together account for >90% followed by medullary cancers with 3% to 5% and anaplastic carcinomas making up <3%. Epigenetic events of DNA hypermethylation are emerging as promising molecular targets for cancer detection. Our immediate and long term goal is to identify DNA methylation markers for early detection of thyroid cancer. This pilot study comprised of 21 patients to include 11 papillary thyroid cancers (PTC), 2 follicular thyroid cancers (FTC), 5 normal thyroid cases, and 3 hyperthyroid cases. Aberrant promoter methylation was examined in 24 tumor suppressor genes using the methylation specific multiplex ligation-dependent probe amplification (MS-MLPA) assay and in the NIS gene using methylation-specific PCR (MSP). The frequently methylated genes were CASP8 (17/21), RASSF1 (16/21) and NIS (9/21). In the normal samples, CASP8, RASSF1 and NIS were methylated in 5/5, 4/5 and 1/5 respectively. In the hyperthyroid samples, CASP8, RASSF1 and NIS were methylated in 3/3, 2/3 and 1/3 respectively. In the thyroid cancers, CASP8, RASSF1, and NIS were methylated in 9/13, 10/13, and 7/13 respectively. CASP8, RASSF1 and NIS were also methylated in concurrently present normal thyroid tissue in 3/11, 4/11 and 3/11 matched thyroid cancer cases (matched for presence of both normal thyroid tissue and thyroid cancer), respectively. Our data suggests that aberrant methylation of CASP8, RASSF1, and NIS maybe an early change in thyroid tumorigenesis regardless of cell type.
PMCID: PMC3129708  PMID: 21738852
Papillary thyroid cancer; Follicular thyroid cancer; hypermethylation; NIS; CASP8; RASSF1
24.  DNA Methylation in Thyroid Tumorigenesis 
Cancers  2011;3(2):1732-1743.
Thyroid cancer is the most common endocrine cancer with 1,690 deaths each year. There are four main types of which the papillary and follicular types together account for >90% followed by medullary cancers with 3% to 5% and anaplastic carcinomas making up <3%. Epigenetic events of DNA hypermethylation are emerging as promising molecular targets for cancer detection. Our immediate and long term goal is to identify DNA methylation markers for early detection of thyroid cancer. This pilot study comprised of 21 patients to include 11 papillary thyroid cancers (PTC), 2 follicular thyroid cancers (FTC), 5 normal thyroid cases, and 3 hyperthyroid cases. Aberrant promoter methylation was examined in 24 tumor suppressor genes using the methylation specific multiplex ligation-dependent probe amplification (MS-MLPA) assay and in the NIS gene using methylation-specific PCR (MSP). The frequently methylated genes were CASP8 (17/21), RASSF1 (16/21) and NIS (9/21). In the normal samples, CASP8, RASSF1 and NIS were methylated in 5/5, 4/5 and 1/5 respectively. In the hyperthyroid samples, CASP8, RASSF1 and NIS were methylated in 3/3, 2/3 and 1/3 respectively. In the thyroid cancers, CASP8, RASSF1, and NIS were methylated in 9/13, 10/13, and 7/13 respectively. CASP8, RASSF1 and NIS were also methylated in concurrently present normal thyroid tissue in 3/11, 4/11 and 3/11 matched thyroid cancer cases (matched for presence of both normal thyroid tissue and thyroid cancer), respectively. Our data suggests that aberrant methylation of CASP8, RASSF1, and NIS maybe an early change in thyroid tumorigenesis regardless of cell type.
PMCID: PMC3129708  PMID: 21738852
papillary thyroid cancer; follicular thyroid cancer; hypermethylation; NIS; CASP8; RASSF1
25.  Differential DNA methylation profiles in gynecological cancers and correlation with clinico-pathological data 
BMC Cancer  2006;6:212.
Epigenetic gene silencing is one of the major causes of carcinogenesis. Its widespread occurrence in cancer genome could inactivate many cellular pathways including DNA repair, cell cycle control, apoptosis, cell adherence, and detoxification. The abnormal promoter methylation might be a potential molecular marker for cancer management.
For rapid identification of potential targets for aberrant methylation in gynecological cancers, methylation status of the CpG islands of 34 genes was determined using pooled DNA approach and methylation-specific PCR. Pooled DNA mixture from each cancer type (50 cervical cancers, 50 endometrial cancers and 50 ovarian cancers) was made to form three test samples. The corresponding normal DNA from the patients of each cancer type was also pooled to form the other three control samples. Methylated alleles detected in tumors, but not in normal controls, were indicative of aberrant methylation in tumors. Having identified potential markers, frequencies of methylation were further analyzed in individual samples. Markers identified are used to correlate with clinico-pathological data of tumors using χ2 or Fisher's exact test.
APC and p16 were hypermethylated across the three cancers. MINT31 and PTEN were hypermethylated in cervical and ovarian cancers. Specific methylation was found in cervical cancer (including CDH1, DAPK, MGMT and MINT2), endometrial cancer (CASP8, CDH13, hMLH1 and p73), and ovarian cancer (BRCA1, p14, p15, RIZ1 and TMS1). The frequencies of occurrence of hypermethylation in 4 candidate genes in individual samples of each cancer type (DAPK, MGMT, p16 and PTEN in 127 cervical cancers; APC, CDH13, hMLH1 and p16 in 60 endometrial cancers; and BRCA1, p14, p16 and PTEN in 49 ovarian cancers) were examined for further confirmation. Incidence varied among different genes and in different cancer types ranging from the lowest 8.2% (PTEN in ovarian cancer) to the highest 56.7% (DAPK in cervical cancer). Aberrant methylation for some genes (BRCA1, DAPK, hMLH1, MGMT, p14, p16, and PTEN) was also associated with clinico-pathological data.
Thus, differential methylation profiles occur in the three types of gynecologic cancer. Detection of methylation for critical loci is potentially useful as epigenetic markers in tumor classification. More studies using a much larger sample size are needed to define the potential role of DNA methylation as marker for cancer management.
PMCID: PMC1560388  PMID: 16928264

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