大肠癌组织DCC基因启动子甲基化及表达水平相关性研究

目的:探讨结直肠癌缺失基因 (DCC)在大肠癌组织中的表达特征及其与启动子甲基化的相关性.方法:分别采用免疫组织化学和甲基化特异性PCR (MSP)方法检测71例大肠癌及其相应癌旁组织中DCC蛋白的表达情况及DCC基因启动子甲基化状态.结果:大肠癌组织中DCC蛋白表达水平 (35/71, 49.3%) 显著低于癌旁正常组织 (34/39, 87.2%, P<0.001),且与临床Duke分期相关,P=0.023;大肠癌组织中DCC基因启动子甲基化发生率 (54/71, 76.1%)高于癌旁正常组织 (14/39, 35.9%, P<0.001)和癌旁炎性组织 (10/22, 45.5%, P=0.007),且直肠癌患者DCC基因启动子甲基化发生率 (28/31, 90.3%)高于结肠癌患者 (27/40, 67.5%, P=0.022);大肠癌组织中DCC蛋白失表达组甲基化发生率 (34/36, 94.4%)显著高于DCC蛋白表达组 (20/35, 57.1%, P<0.001).结论:DCC基因启动子甲基化可能是大肠癌中DCC失表达的主要机制之一.     

胃癌组织及相关淋巴结中端粒酶逆转录酶基因启动子区域甲基化检测的临床意义

[目的]检测胃癌患者肿瘤组织及其相应的癌旁组织和淋巴结组织中端粒酶逆转录酶(hTERT)基因启动子区域甲基化状态,并探讨其甲基化状态的改变与临床病理特征的关系.[方法]运用甲基化特异性PCR(MSP)方法,检测52例手术切除胃癌组织、癌旁组织及相关淋巴结中hTERT基因启动子区域甲基化状念、以同一标本正常组织作为阴性对照.[结果]正常胃黏膜组织未检测出hTERT表达、胃癌组织及癌旁组织、转移淋巴结中均检测出hTERT表达.转移淋巴结、胃癌组织中hTERT基因的甲基化阳性率分别为81.6％(31/38)、71.1％(37/52),明显高于癌旁组织的29.5％(13/52)(P＜0.01).胃癌组织hTERT基因甲基化阳性率与胃癌的临床分期、组织分化程度、肿瘤大小有相关性(P＜0.05).癌旁组织hTERT基因甲基化阳性率和胃癌的临床分期、肿瘤大小、组织分化程度、淋巴结转移具有相关性(P＜0.05).转移淋巴结hTERT基因 甲基化阳性率则与临床及病理特征无关.[结论]胃癌组织及转移淋巴结中存在hTERT基因启动子区域的异常甲基化调控、可能参与了胃癌的发生与发展.     

大肠肿瘤Syndecan-2基因甲基化及临床意义

目的探讨Syndecan-2(SDC2)基因甲基化对大肠肿瘤的诊断价值并分析其与临床病理特征和预后的关系。方法收集2014年1月至2016年12月大肠癌及配对癌旁石蜡组织各54例以及大肠腺瘤石蜡组织30例,另收集2018年8月至2019年5月大肠癌患者粪便32例、大肠腺瘤患者粪便28例及正常人群粪便40例。通过定量甲基化特异性PCR(QMSP)检测各样本中SDC2基因启动子区甲基化的发生率,分析SDC2基因甲基化检出率与临床病理特征的关系,并比较不同SDC2甲基化水平大肠癌患者的总生存期(OS)。结果SDC2基因甲基化在大肠癌、大肠腺瘤和癌旁组织中的阳性率分别为85.2%(46/54)、66.7%(20/30)和5.6%(3/54),在大肠癌患者、大肠腺瘤患者和正常人群粪便中的阳性率分别为78.1%(25/32)、57.1%(16/28)和2.5%(1/40)。与癌旁组织比较,SDC2甲基化在大肠癌组织和大肠腺瘤组织中均更易被检测到(P=0.000,P=0.000);SDC2甲基化阳性率在大肠癌患者粪便和大肠腺瘤患者粪便中明显高于正常人群粪便(P=0.000,P=0.000)。对于组织或粪便样本,大肠癌与大肠腺瘤SDC2甲基化阳性率的差异无统计学意义(P>0.05)。对于组织和粪便样本,SDC2基因甲基化与大肠癌和大肠腺瘤临床病理特征均无关(P>0.05)。与正常粪便比较,SDC2基因甲基化筛查大肠癌和大肠腺瘤的灵敏度分别为78.1%和57.1%,特异度均为97.5%。大肠癌组织SDC2基因甲基化低水平组的中位OS为68.0个月,与高水平组的70.0个月比较,差异无统计学意义(P=0.752)。结论SDC2基因甲基化是筛查大肠癌的有效分子标志物,但对大肠癌的预后无明显指导意义。     

Kiss-1基因启动子甲基化与结直肠癌的关系

目的探讨结直肠癌组织中Kiss-1基因启动子甲基化状态与临床病理学特征的关系及临床意义。方法采用甲基化特异性PCR检测142例正常结直肠组织、23例结直肠腺瘤组织、73例结直肠癌组织和相应癌旁组织中Kiss-1基因启动子甲基化状态。结果结直肠癌组织中Kiss-1基因启动子甲基化阳性率为82.2%,癌旁组织为30.1%,结直肠腺瘤组织为21.7%,正常结直肠组织为6.3%,总体比较差异有统计学意义(P<0.05)。Kiss-1基因启动子甲基化阳性率与结直肠癌的分化程度、浸润深度、淋巴结转移及远处转移有关(P<0.05)。结论 Kiss-1基因启动子甲基化可能促进结直肠癌的发生、发展与转移,Kiss-1基因启动子甲基化水平有可能成为评估结直肠癌转移风险及预后的指标之一。     

散发性乳腺癌患者血浆BRCA1基因启动子异常甲基化的检测

目的:探讨散发性乳腺癌组织及外周血浆中BRCA1基因启动子异常甲基化状况及其在散发性乳腺癌诊断中的价值。方法:用甲基化特异PCR方法对散发性乳腺癌患者癌组织、癌旁组织及相应血浆进行BRCA1异常甲基化检测。结果:93例散发性乳腺癌组织中,BRCA1基因启动子异常甲基化率为29%(27/93),相应血浆中BRCA1的甲基化检出率为24.7%(23/93),而癌旁组织、正常对照血浆未检出甲基化,只检出未甲基化的BRCA1。血浆中甲基化改变与肿瘤组织甲基化状况显著相关(P<0.05);BRCA1异常甲基化与髓样癌和粘液腺癌的组织分型显著相关(P<0.05),也与肿瘤淋巴结转移显著相关(P<0.005);但与散发性乳腺癌患者年龄(绝经与否)及肿瘤分级无显著的相关性(P>0.05)。结论:血浆BRCA1基因异常甲基化改变的检测在散发性乳腺癌的特异诊断、组织分型和淋巴结恶性转移等方面有一定的应用价值。     

肝细胞癌ASC基因启动子区甲基化及其mRNA表达研究

目的:探讨肝细胞肝癌(HCC)ASC基因启动子区甲基化与mRNA表达及其临床病理特征的关系.方法:运用甲基化特异性聚合酶链反应(MSP)和实时荧光定量PCR技术,检测58例肝细胞癌及其相应癌旁组织、15例肝硬化肝组织、5例慢性病毒性肝炎肝组织和5例正常肝组织中ASC基因启动子区甲基化状态及其mRNA的表达水平.结果:58例肝细胞癌组织中有40例(69.0%)发生ASC基因启动子区甲基化,其相应癌旁组织中有27例(46.6%)发生该基因启动子区甲基化,而在肝硬化、肝炎和正常肝组织中均未检测到该基因启动子区甲基化.ASC基因在肝细胞癌组织中甲基化频率高于其相应癌旁组织(P=0.015).ASC基因启动子区甲基化与肿瘤直径(P=0.001)、生长方式(P=0.003)以及国际抗癌联盟第6版TNM(TNM6)分期(P=0.001)有关.以ASC基因在正常肝组织中的表达量为参照,58例肝细胞癌组织中有33例出现ASC基因mRNA低表达或表达缺失,其相应癌旁组织中有14例出现低表达或表达缺失,而在肝硬化及肝炎肝组织中ASC基因mRNA均呈正常表达.与癌旁组织相比,肝细胞癌组织中ASC基因mRNA表达明显下调(P<0.05).在发生ASC基因启动子区甲基化的40例肝细胞癌组织中有26例出现mRNA低表达.结论:ASC基因启动子区甲基化是肝细胞癌中的频发事件,可能在肝细胞癌的进展中起重要作用.     

肺癌E-cadherin基因启动子CpG岛甲基化的研究

目的检测肺癌组织、相应的癌旁组织及正常肺组织中E-cadherin基因启动子CpG岛甲基化水平，探讨肺癌的发病机制。方法采用甲基化特异性PCR技术检测22例肺癌组织、相应的癌旁组织和9例正常肺组织中E-cad-herin基因启动子CpG岛甲基化水平。结果肺癌中E-cadherin基因启动子CpG岛完全甲基化率为13.6%（3/22），部分甲基化率为27.3%（6/22），总甲基化率为40.9%（9/22），显著高于相应癌旁组织中该基因的甲基化率9.1%（2/22）。9例正常肺组织中该基因未发生甲基化。此外，E-cadherin基因启动子CpG岛异常甲基化与患者性别、年龄无关，甲基化的发生率随着肿瘤的分期早晚有上升的趋势。结论E-cadherin基因启动子CpG岛的异常甲基化是肺癌发生中的常见分子事件，可能参与了肺癌的发生发展过程。     

DNA修复基因MGMT启动子区过甲基化与食管鳞状细胞癌

目的：O^6－甲基鸟嘌呤DNA甲基转移酶（MGMT）可以转移DNA加合物O^6－甲基鸟嘌呤中的甲基,从而修复DNA损伤,许多肿瘤中发现MGMT基因启动子过甲基化导致该基因失活,我们研究了MGMT基因启动子甲基化状态与食管癌的关系。方法：采用甲基化特异性聚合酶链反应及测序方法分析食管癌。癌旁组织和正常食管上皮中MGMT启动子甲基化状态。结果：在检测的199例食管癌组织中,46例（38．7％）有MGMT基因启动子过甲基化,相应癌旁组织22例中也有5例（22．7％）出现MGMT基因甲基化,而21例正常食管上皮均无此种改变。结论：MGMT基因启动子过甲基化是食管癌中常见的分子事件,可能发生在癌过程的早期阶段。     

胃癌组织RUNX3和CHFR基因启动子高甲基化的研究

目的:检测胃癌患者肿瘤组织及其相应的癌旁组织中RUNX3和CHFR基因启动子区域甲基化状态,并探讨其甲基化状态的改变与临床病理特征的关系.方法:将2007年3月至2007年9月间42例胃癌患者(男:女=34:8)的手术切除标本分为两组:一组是肿瘤组织,另一组是相应癌旁组织.胃癌患者术前均未行放疗和化疗,癌旁组织取自肿瘤组织5cm以外.采用酚-氯仿抽提法提取组织DNA,甲基化特异性PCR法(MSP)检测肿瘤组织及相应癌旁正常组织(各42例)中RUNX3和CHFR启动子区域甲基化状态,并用1.5%的琼脂糖凝胶对PCR产物进行电泳分析.结果:54.7%和40.4%的胃癌组织中分别存在RUNX3和CHFR基因异常甲基化,而相应的癌旁正常组织中这两个基因的甲基化率均是7.1%,癌组织中RUNX3和CHFR基因的异常甲基化率显著高于相应的癌旁正常组织(PRUNX3<0.05,PCHFR<0.05).胃癌组织中该两基因的甲基化与肿瘤大小显著相关(PRUNX3<0.05,PCHFR<0.05),但与患者年龄(PRUNX3=0.711,PCHFR=0.845)、性别(PRUNX3=0.764,pCHFR=0.849)、肿瘤浸润深度(PRUNX3=0.276,PCHFR=0.542)、组织分化程度(PRUNX3=0.491,PCHFR=0.695)、病理分期(PRUNX3=0.555,PCHFR=0.237)以及淋巴结受累(PRUNX3=0.155,PCHFR=0.124)等临床病理特征无关.结论:RUNX3和CHFR基因启动子区的异常甲基化是胃癌发生发展中的频繁事件,在胃癌的发生中具有肿瘤特异性.通过检测胃黏膜中RUNX3和CHFR的甲基化状态,对于胃癌的早期诊断具有一定的参考价值.     

Methyl-CpG binding column-based identification of nine genes hypermethylated in colorectal cancer

DNA methylation is an epigenetic event that plays a role in gene expression regulation. Alterations in DNA methylation contribute to cancer development and progression. The aim of this study was to identify gene promoters aberrantly methylated in colorectal tumor tissue in comparison to normal colonic mucosa. Analyses were performed on two pooled DNA samples: from normal and cancerous tissue obtained from CRC patients. DNA was fractionated according to methylation degree with the use of affinity column containing methyl-CpG binding domain. To identify novel hypermethylated gene promoters, methylated DNA from normal and from cancerous tissues were analyzed with the use of promoter microarrays. We identified nine novel genes hypermethylated in colorectal cancer. The frequency of their promoter methylation was assessed in the larger group of patients (n = 77): KCNK12 (methylated in 41% of CRC patients), GPR101 (40%), CDH2 (45%), BARX1 (56%), CNTFR (22%), SYT6 (64%), SMO (21%), EPHA5 (43%), and GSPT2 (21%). The results of gene expression level analysis suggest the role of promoter methylation in downregulation of six out of nine genes examined. We did not find correlation between gene methylation and age, gender, tumor grade or stage. Importantly, in stage IV CRC methylation of GPR101 correlated with longer time to progression (P = 0.0042; HR = 2.5468; 95% CI 1.5391-10.0708).     

选择性剪接基因RBFOX1在食管鳞癌中的研究

背景与目的：选择性剪接是基因表达中的重要调控机制,异常的剪接可导致细胞周期异常、癌基因转录因子激活及抑癌基因转录因子失活;异常剪接与肿瘤发生、发展息息相关。DNA甲基化是表观遗传修饰的重要组成部分,基因启动子的异常甲基化可导致基因沉默,抑癌基因和DNA修复基因的高甲基化参与多种肿瘤的发生;另外DNA甲基化还是选择性剪接的关键参数,DNA异常甲基化影响选择性剪接的平衡。本研究通过对食管鳞癌组织标本中RBFOX1(RNA binding protein, fox-1 homolog 1)选择性剪接基因的甲基化水平和表达进行检测,探讨其临床应用价值。方法：在149例配对的食管鳞癌及癌旁组织中,运用MassARRAY对RBFOX1基因的甲基化水平进行检测,并从同一批样品中选取42对组织采用RT-PCR进行RBFOX1基因的mRNA表达分析,统计甲基化水平与食管鳞癌主要临床病理特征的关系。结果：在食管鳞癌组织标本中,RBFOX1的甲基化水平为41.8%,明显低于对应癌旁组织的68.3%。差异有统计学意义(P<0.01);RBFOX1的甲基化水平与患者的性别、年龄、吸烟、饮酒以及肿瘤的分化、分期等无明显相关。依据癌组织中甲基化水平阈值（33.6%）=Mean(癌旁组织)-2.5SD(标准差),将研究对象分为两组,低于阈值的一组定义为组1,高于阈值的为组2。组1和组2的5年总体生存率(overall survival,OS)为57.0%和35.7%。差异无统计学意义(P=0.06)。组1和组2的5年无进展生存率(progression-free survival,PFS)为48.7%和28.9%。差异有统计学意义(P=0.03)。多因素分析结果显示仅TNM分期为生存的独立预测因子。结论：选择性剪接基因RBFOX1在食管鳞癌组织中的甲基化水平和表达水平均低于癌旁组织,RBFOX1启动子区的甲基化水平不能作为生存分析的预测因子。     

Promoter hypermethylation of RASSF1A, MGMT, and HIC-1 genes in benign and malignant colorectal tumors

Hypermethylation at the promoter region is an important epigenetic mechanism underlying the inactivation of tumor suppressor genes and frequently occurs as an early event in the development of different types of cancer including colorectal carcinoma (CRC). The aim of the present study is the detection of methylation status for some tumor suppressor genes including RASSF1A, MGMT, and HIC-1 in both cancerous and precancerous lesions of colorectal mucosa to evaluate the possibility of developing epigenetic biomarker for early detection of Egyptian CRC. Tissue biopsy was collected from 72 patients (36 CRC, 17 adenomatous polyps, and 19 ulcerative colitis), and in addition, adjacent normal-appearing tissues were collected as control. Promoter hypermethylation status for RSSAF1A, MGMT, and HIC-1 genes was detected after isolation of genomic DNA from the tissues samples using methylation-specific PCR technique. High frequency of methylation at MGMT, RASSFA, and HIC-1 was detected in CRC patients (25%, 47.2%, and 41.7% respectively). The highest methylation detected in adenomatous polyps patients was in MGMT gene (47.1%) followed by 35.3% for HIC-1 and only 5.9% for RASSF1A gene. HIC-1 gene exhibited highest frequency of methylation in ulcerative colitis patients (57.8%) whereas it was 26.3% for both RASSF1A and MGMT genes. A nonsignificant association was recorded between the methylation status in different genes examined with the clinicopathological factors except the association between methylation at RASSF1A gene with gender (p?=?0.005), and it was significant. In conclusion, aberrant hypermethylation at promoter region of RASSFA, MGMT, and HIC-1 genes is involved in Egyptian CRCs. Hypermethylation of MGMT and HIC-1 genes plays an important role in the initiation of disease especially ulcerative colitis–carcinoma pathway.     

Identification of GABRA1 and LAMA2 as new DNA methylation markers in colorectal cancer

Aberrant methylation of CpG islands in the promoter region of genes is a common epigenetic phenomenon found in early cancers. Therefore conducting genome-scale methylation studies will enhance our understanding of the epigenetic etiology behind carcinogenesis by providing reliable biomarkers for early detection of cancer. To discover novel hypermethylated genes in colorectal cancer by genome-wide search, we first defined a subset of genes epigenetically reactivated in colon cancer cells after treatment with a demethylating agent. Next, we identified another subset of genes with relatively down-regulated expression patterns in colorectal primary tumors when compared with normal appearing-adjacent regions. Among 29?genes obtained by cross-comparison of the two gene-sets, we subsequently selected, through stepwise subtraction processes, two novel genes, GABRA1 and LAMA2, as methylation targets in colorectal cancer. For clinical validation pyrosequencing was used to assess methylation in 134 matched tissue samples from CRC patients. Aberrant methylation at target CpG sites in GABRA1 and LAMA2 was observed with high frequency in tumor tissues (92.5% and 80.6%, respectively), while less frequently in matched tumor-adjacent normal tissues (33.6% for GABRA1 and 13.4% for LAMA2). Methylation levels in primary tumors were not significantly correlated with clinico-pathological features including age, sex, survival and TNM stage. Additionally, we found that ectopic overexpression of GABRA1 in colon cancer cell lines resulted in strong inhibition of cell growth. These results suggest that two novel hypermethylated genes in colorectal cancer, GABRA1 and LAMA2, may have roles in colorectal tumorigenesis and could be potential biomarkers for the screening and the detection of colorectal cancer in clinical practice.     

食管鳞癌中p16基因启动子区甲基化及其表达

 目的探讨食管鳞癌（ESCC）p16基因甲基化的状况及其表达与食管鳞癌临床病理特征之间的关系。方法采用甲基化特异性PCR方法（MSP）分别检测75例食管癌组织、癌旁组织和切缘组织p16基因启动子区域CpG岛甲基化状态。采用Envision免疫组化法检测食管癌组织及癌旁组织的p16蛋白的表达。结果75例标本中，食管癌组织、癌旁组织和切缘细织p16基因甲基化率分别为41．3％（31／75）、13．3％（10／75）和6．67％（5／75）。癌组织和癌旁组织P16蛋白的阳性表达率分别为29．3％（22／75）和56．7％0（17／30）。31例癌组织p16基因甲基化阳性标本中有2例（6．4％）检测到P16蛋白的表达，而44例癌组织p16基因甲基化阴性标本中有20例（45．5％）检测到P16蛋白的表达。食管癌组织p16基因甲基化率显著高于癌旁组织和切缘组织（P〈0.01），P16蛋白表达与p16基因甲基化呈负相关。p16基因启动子区甲基化与食管癌的组织学分级、肿瘤部位无明显相关，与临床分期、淋巴转移密切相关。结论p16基因甲基化在食管癌发生发展中起着重要作用，食管鳞癌的分期和淋巴结转移与p16基因甲基化之间有密切关系。     

Aberrant promoter methylation of p16 in colorectal adenocarcinoma in North Indian patients

AIM: To investigate p16 gene methylation and its expression in 30 patients with sporadic colorectal adenocarcinoma in a North Indian population.METHODS: Methylation specific polymerase chain reaction was used to detect p16 gene methylation and immunohistochemistry was used to study the p16 expression in 30 sporadic colorectal tumors as well as adjoining and normal tissue specimens.RESULTS: Aberrant promoter methylation of p16 gene was detected in 12 (40%) tumor specimens, whereas no promoter methylation was observed in adjoining and normal tissue. Immunohistochemistry showed expression of p16 protein in 26 (86.6%) colorectal tumors whereas complete loss of expression was seen in 4 (13.3%) and reduced expression was observed in 12 (40%) tumors. In the adjoining mucosa, expression of p16 was in 11 (36.6%) whereas no clear positivity for p16 protein was seen in normal tissue. There was a significant difference in the expression of p16 protein in tumor tissue and adjoining mucosa (P < 0.001). The methylation of the p16 gene had a significant effect on the expression of p16 protein (P = 0.021). There was a significant association of methylation of p16 gene with the tumor size (P = 0.015) and of the loss/reduced expression of p16 protein with the proximal site of the tumor (P = 0.047). Promoter methylation and expression of p16 had no relation with the survival of the patients (P > 0.05).CONCLUSION: Our study demonstrated that promoter hypermethylation of the p16 gene results in loss/reduced expression of p16 protein and this loss/reduced expression may contribute to tumor enlargement.     

Promoter methylation of leukemia inhibitory factor receptor gene in colorectal carcinoma

Aberrant methylation of gene promoters and corresponding loss of gene expression plays a critical role in the initiation and progression of colorectal cancer. An IL-6-type cytokine receptor, leukemia inhibitory factor receptor (LIFR), is a component of cell-surface receptor complexes for multifunctional cytokines such as LIF. Herein, we report that LIFR is methylated in human colon cancer. LIFR promoter was methylated in primary tumor tissues with high frequency (65%, 52/80). Quantitative methylation-specific PCR (TaqMan-MSP) demonstrated differential promoter methylation of LIFR in primary colorectal cancer tissues as compared to normal colon tissues (5%, 4/80). LIFR methylation was not detectable in 13 normal colon mucosa samples obtained from patients without cancer. The mRNA expression of LIFR was significantly down-regulated in colon cancer tissues as compared to corresponding normal tissues. A strong expression of LIFR protein was observed in all non-malignant normal and adjacent normal colon mucosa tissues whereas down-regulated LIFR protein expression was observed in primary tumors. These results demonstrate that cancer-specific methylation and a specific decrease of LIFR expression are a common inactivation event in colon cancer development.     

Methylation and regulation of expression of different retinoic acid receptor beta isoforms in human colon cancer

Tumor suppressor genes can become inactivated in cancer via hypermethylation of their promoter. The retinoic acid receptor beta (RARbeta) gene is expressed from two distinct promoters, both of which have CpG islands. RARbeta1 is expressed primarily during embryogenesis, whereas RARbeta2 is expressed in adult tissues and hypermethylated in a number of cancer cells. We used combined bisulfite restriction analysis to evaluate their methylation in colorectal mucosa and tumors. Methylation of RARbeta1 was detected, with a mean of 2% in normal colon tissues in young subjects (< 32 years), and 16% in older subjects (> 75 years) (P < 0.001). Using paired normal/tumor tissue samples, we found higher mean methylation rate in tumors than in adjacent normal tissue (mean, 46% versus 16%; P < 0.001) and hypermethylation of RARbeta1 in all eight cell lines examined. By RT-PCR, RARbeta1 was not expressed in normal adult colon tissues and its expression could not be efficiently activated in most cell lines by the DNA methyltransferase inhibitor 5-aza-2'-deoxycytidine (5-Aza-CdR). RARbeta2 methylation was also observed in normal colon tissues and was lower in young individuals than in older ones (mean, 11% versus 23%; P < 0.05). Among paired samples, RARbeta2 methylation was higher in tumor tissue than in normal tissue in 14 cases, vice versa in 7 cases, and equal in 6 cases. All eight cell lines were hypermethylated and did not express RARbeta2, but RARbeta2 expression could be reactivated easily by 5-Aza-CdR. We suggest that the embryonic RARbeta1 isoform is readily hypermethylated in aging colon mucosa and all colorectal cancers because of its lack of expression in normal tissues. The adult RARbeta2 isoform also shows age-related methylation in normal tissues but more variable methylation in colorectal cancer, perhaps because its expression offers continued protection against methylation or its silencing does not provide a selective advantage in the early stages of the disease.