结直肠癌中的微卫星不稳定现象

微卫星不稳定DNA标记目前已被广泛用于基因作图的遗传标记、遗传疾病致病基因的连锁分析及基因位点缺失或杂合性缺失的研究。因微卫星不稳定高频型结直肠癌有其特殊的临床特征 ,因此微卫星不稳定现象对临床有重要的指导意义。对微卫星不稳定现象可能的原因、微卫星不稳定高频型结直肠癌的临床特征及微卫星不稳定现象与抑癌基因的关系作一简单综述     

结直肠癌中的微卫星不稳定现象

微卫星不稳定DNA标记目前已被广泛用于基因作图的遗传标记、遗传疾病致病基因的连锁分析及基因位点缺失或杂合性缺失的研究.因微卫星不稳定高频型结直肠癌有其特殊的临床特征,因此微卫星不稳定现象对临床有重要的指导意义.对微卫星不稳定现象可能的原因、微卫星不稳定高频型结直肠癌的临床特征及微卫星不稳定现象与抑癌基因的关系作一简单综述.     

结直肠癌中的微卫生不稳定现象

微卫星不稳定DNA标记目前已被广泛用于基因作图的遗传标记、遗传疾病致病基因的连锁分析及基因位点缺失或杂合性缺失的研究。因微卫星不稳定高频型结直肠癌有其特殊的临床特征，因此微卫星不稳定现象对临床有重要的指导意义。对微卫星不稳定现象可能的原因、微卫星不稳定高频型结直肠癌的临床特征及微卫星不稳定现象与抑癌基因的关系作一简单综述。     

结直肠癌微卫星不稳定（MSI）与其发病及预后的关系

抑癌基因及癌基因之间的相互作用是结直肠癌发病主要发病原因,近年研究发现微卫星不稳定成为结直肠癌发病另一重要机制,尤其是遗传性非息肉病性结直肠癌（hereditary non-polyposis colorectal cancer,HNPCC）及部分散发性结直肠癌发生的重要原因。微卫星不稳定的结直肠患者具有独特的临床病理特征,如低分化、黏液腺癌、多位于右半结肠、淋巴细胞浸润明显等。化疗是结直肠癌患者手术后重要治疗手段,氟尿嘧啶类药物为结直肠癌患者化疗的基本药物,因此结直肠癌患者对于氟尿嘧啶类药物敏感性成为患者能否从化疗中获益的重要因素,也成为各位学者的研究热点。近年来有学者提出微卫星不稳定及其他分子标记物可预测结直肠癌患者化疗敏感性,同时也可成为判断预后的指标。微卫星不稳定将来可成为结直肠癌患者的预后及化疗敏感性的判断因素,也可为个体化治疗提供理论依据,但目前尚需大样本的前瞻性临床试验进一步证实。结直肠癌目前在国内外发病率均逐渐升高,成为危害人类生命的重要疾病,且遗传倾向明显,是目前人类恶性肿瘤中遗传变化最明显的肿瘤。对于结直肠癌的发病研究表明,染色体不稳定（chromosome instability）为结直肠癌发病的主要原因,其机制仍未完全阐明。近年的研究发现微卫星不稳定（microsatelite instability）为结直肠癌发病的另一重要机制,是遗传性非息肉病性结直肠癌（heredi? tary non-polyposis colorectal cancer,HNPCC）及部分散发性结直肠癌发生的重要原因。目前关于微卫星不稳定的研究不仅于发病机制上,与结直肠癌预后的关系也成为目前研究的热点。      

微卫星高度不稳定或错配修复缺陷结直肠癌新辅助免疫治疗的探讨和展望

微卫星高度不稳定（microsatellite instability-high,MSI-H）或错配修复缺陷（mismatch repair-deficient,dMMR）结直肠癌对传统新辅助治疗方案的敏感性较低，免疫治疗的出现改变了MSI-H/dMMR结直肠癌的治疗格局。从晚期疾病的后线治疗到一线治疗，甚至在早期结直肠癌的新辅助治疗，免疫治疗均展现出优异的疗效。全文探讨了结直肠癌新辅助免疫治疗的最新研究进展、目前存在的问题以及未来的发展方向，以期在临床实践过程中为MSI-H/d MMR结直肠癌患者制定个体化治疗方案提供参考。     

散发性结直肠癌染色体5q14区杂合性缺失精细定位

目的:研究散发性结直肠癌五号染色体杂合性缺失,对5q14区精细定位,寻找新的结直肠癌抑癌基因. 方法: 五号染色体采用16个微卫星DNA标记,在5q14区另取7个微卫星标记对83例结直肠癌病例的肿瘤和正常组织进行PCR反应.PCR产物在ABI Prism 377自动荧光测序仪进行电泳3小时,以 GeneScan 3.1和Genotyper 2.1软件进行基因分型. 结果: 在五号染色体上发现了三个高频杂合缺失区即5p15、5q14和5q22区.对5q14区再用7对微卫星标记引物行精细定位,界定了三个精细的高频杂合缺失区域. 结论: 通过精细杂合缺失作图研究,在5q14区发现三个精细的杂合缺失区域,该区很可能存在一个或多个与结直肠癌相关的新的抑癌基因.     

散发性结直肠癌患者5号染色体杂合缺失分析

目的：探讨散发性结直肠癌患者5号染色体上与抑癌基因相关的杂合缺失（LOH）情况,并探讨新的抑癌基因位点,方法：对83例散发性结直肠癌患者基因组DNA,以15个不同荧光标记的高度多态性微卫星引物（平均遗传距离12．67cm)扩增相应的微卫星位点,用ABI PRISM 377测序仪进行基因扫描,统计各位点杂合缺失率。结果：在15个微卫星位点中,平均杂合缺失率为25．80％,5p中最高为D5S416,占48．15％,5q中最高为D5S471,占38．71％,D5S471周围的3个位点（D5S428,D5S2027 和 D5S2115）也存在高频的杂合缺失（＞30．00％）,结论：5号染色体上存在着高频的杂合缺失,其中5q13.3-31.1区域中,有与结直肠癌发生密切相关的APC,MCC,CTNNA1及IL家族等基因,而在5p15.1上的D5S416的杂合缺失率高达48．15％,此区域至今尚未发现与结直肠癌相关的基因位点,估计可能有未知的抑癌基因存在。     

微卫星不稳定在结直肠癌预后及治疗指导中的研究进展

微卫星不稳定是基因组不稳定的表现之一,其在结直肠癌、乳癌、肺癌以及淋巴瘤等多种恶性肿瘤中均有存在,并且对肿瘤的发生、发展以及预后转归起到关键作用。近年来,国内外学者对微卫星不稳定的相关研究取得了显著成果,尤其在结直肠癌领域,其对结直肠癌免疫治疗和化学治疗的指导性意见已被纳入诊疗指南,并且成为该病治疗以及预后指导上的重要分子指标。本文就此总结国内外相关研究进展,以期为后续研究工作提供指导。     

结直肠癌组织MSI状态及其与临床病理参数之间的相关性

目的:分析结直肠癌组织微卫星不稳定（MSI）状态及其与临床病理参数之间的相关性。方法:利用免疫组化法检测MLH1、MSH2、MSH6、PMS2错配修复蛋白的表达,分析441例结直肠癌组织的MSI状态。结果:免疫组化检测发现,441例结直肠癌中,微卫星稳定（MSS）为375例,MLH1、MSH2、MSH6、PMS2错配修复蛋白任一表达缺失共66例,占14.97%（66/441）;其中MLH1、MSH2、MSH6、PMS2单一表达缺失率分别为1.4%（6/441）、0.2%（1/441）、0.7%（3/441）、2.3%（10/441）;MLH1和PMS2同时表达缺失率9.1%（40/441）,MSH2和MSH6同时表达缺失率1.1%（5/441）,MSH6和PMS2同时表达缺失率0.2%（1/441）。结直肠癌患者MSI与MSS在民族、肿瘤部位、分化程度、T分期、N分期、肿瘤大小等临床病理特征方面存在差异,而在性别、年龄、大体类型、病理类型、M分期、临床分期、神经和脉管侵犯方面均无明显差异。结论:新疆少数民族、右半结肠、低分化、T4、N0、肿瘤＞5 cm的结直肠癌患者更易发生MSI。     

错配修复系统hMutS、hMutL的变异与结直肠癌的相关性研究进展

DNA错配修复系统（mismatch repair system,MMR）是重要的复制后修复机制,修复各种类型的碱基错配和插入/缺失环。hMutS、hMutL是MMR中重要的两个子系统,它们的功能缺陷与多种肿瘤,尤其结直肠癌密切相关。hMutS、hMutL系统关键基因SNPs、启动子甲基化水平的变化,都会直接或间接影响MMR的功能,以及由此引起微卫星不稳定性增加,进而影响结直肠癌的发生、发展和预后。本文主要从hMutS、hMutL系统关键基因的SNPs、启动子甲基化和微卫星不稳定三个方面综述了hMutS、hMutL系统关键基因变异与结直肠癌相关性研究的进展。     

Genetic instability in lung cancer: concurrent analysis of chromosomal, mini- and microsatellite instability and loss of heterozygosity

To investigate what kind of genetic instability plays important roles in lung carcinogenesis, we analyzed micro- and minisatellite instability, loss of heterozygosity (LOH) and chromosome instability in 55 cases of lung cancer, including, 10 squamous cell, 5 large cell, and 3 small cell carcinomas, and 37 adenocarcinomas. Analysis of minisatellite instability, the mechanism of which is different from microsatellite instability, has not been reported previously. Minisatellite instability was detected in only one case (1/55, 1.8%), and the frequency of microsatellite instability was low, being found only in three cases (3/55, 5.5%). In contrast, LOH, for at least in one locus, was observed in 27 cases (49.1%). In adenocarcinomas, the frequency of LOH was higher in poorly differentiated compared to more differentiated carcinomas. For chromosome instability, a similar correlation between differentiation grade and instability was observed in adenocarcinomas. And instability was more common in large cell and small cell carcinomas than in adenocarcinomas. Our analysis showed that chromosome instability and LOH, rather than mini- and microsatellite instability, play significant roles in the development of lung cancer.     

肝细胞癌染色体不稳定性的研究进展

肝细胞癌 (hepatocellularcarcinoma ,HCC)的发展是一个多步过程 ,涉及多染色体的改变 ,且与肿瘤的形态和进展相关。在癌前病变 ,由于DNA甲基化的改变、HBV和HCV的侵入、肿瘤抑制基因的点突变或杂合子丢失 (lossofheterozygosity ,LOH )引起基因表达的改变。肿瘤进展期的特征包括许多染色体上肿瘤抑制基因的LOH。不同的HCC结节所观察到的改变常常是不同的 ,表明其在分子水平上的异质性。这些发现表明HCC的发生过程中遗传学的改变也是一个进行性积累的过程。对HCC分子机制的理解可能获得肿瘤分期的新的标记物 ,评价肿瘤形成的相对危险性 ,为肿瘤的治疗提供新的机会     

Microsatellite instability in colorectal cancer

BACKGROUND: Colorectal cancer (CRC) is the third most common cancer in the world. In 75% CRC develops sporadically, in 25% hereditary or as a consequence of inflammatory bowel disease. CRC carcinogenesis develops over many years. The cause of CRC in 85% is chromosomal instability (CIN) and in 15% microsatellite instability (MSI-H), where hereditary nonpolyposis colorectal cancer (HNPCC) represents 10-20%. Microsatellite sequences (MS) are repeated sequences of short stretches of DNA all over the genome. Microsatellite stability (MSS) means MS are the same in each cell of an individual, whereas microsatellite instability (MSI-H) means MS differ in normal and cancer cells of an individual. The cause of MSI-H is a damaged mismatch repair mechanism (MMR), with the most important MMR proteins being MSH2, MLH1 and MSH6. CONCLUSIONS: MSI-H seems to be an important prognostic factor in CRC and an important predictive factor of CRC chemotherapeutic treatment efficacy. Clinical trials conducted until now have shown contradictory findings in different chemotherapeutic settings, adjuvant and palliative; therefore MSI-H is going to be the object of the future research. The future of cancer treatment is in the individualized therapy based on molecular characteristics of the tumour, such as MSI-H in CRC.     

微小卫星体不稳定性频繁表达于胃癌中

 应用放射性PCR为基础的技术对106例系列胃癌DNA微小卫星体不稳定（MIN）进行评估，发现MIN在一个或一个以上座位者占41％（44/106例）胃癌。分析MIN与胃癌临床病理特点的关系发现，MIN在膨胀性生长方式胃癌中的表达明显高于在浸润型生长方式胃癌中的表达（P＜0.005），但MIN的表达在不同的组织学类型，PTNM分期，年龄和性别没有明显区别（P＞0.05）。这些发现揭示MIN可能在相当一部分胃癌，尤其是在传统上认为愈后较好的膨胀性生长方式胃癌的发生发展过程中起着非常重要的作用。     

胆管癌中微卫星不稳定的变化

目的:探讨胆管癌中微卫星不稳定(MSI)的变化。方法:肝外胆管癌标本70例、肝外胆管结石胆管组织40例,饱和氯化钠法提取组织DNA,PCR-SSCP变性聚丙烯酰胺凝胶电泳检测MSI,根据规定标准判定microsatellite stable(MSS),low-frequency MSI(MSI-L)和high-frequency MSI(MSI-H),计算总MSI率。结果:在肝外胆管结石胆管组织、胆管癌(无转移)、胆管癌(区域淋巴结或局部/远处转移)中MSI率分别为5.0%、21.1%、37.5%,高中分化腺癌及低分化腺癌中MSI率分别为32.6%、22.2%。结论:MSI与胆管癌的发生及浸润转移有关。     

中心体异常、基因不稳定性与肿瘤

基因不稳定性是人类肿瘤细胞的显著特征,包括细胞倍体改变及一系列染色体异常,而在肿瘤细胞中还发现伴有中心体异常。异常中心体可产生多极纺锤体,使染色体错误分离及分配不平衡,介导染色体不稳定性(CIN)和非整倍体的形成。因此,中心体异常也是肿瘤细胞的普遍特征,并且可能出现在肿瘤发生的早期阶段。     

Frequent microsatellite instability in non-Hodgkin lymphomas irresponsive to chemotherapy

Microsatellite instability (MSI) in haematopoietic malignancies has been controversial. Particularly in non-Hodgkin lymphoma, the data published to date lack unity. Using a unique fluorescent technique, we found MSI in eight (14%) tumours in a panel of 59 carefully selected non-Hodgkin lymphoma patients. Our fluorescent technique also reveals two qualitatively distinct modes of MSI, i.e. Type A and Type B. Based on our previous studies using DNA mismatch repair (MMR) gene-knock out animals, we have concluded that Type A MSI is a direct consequence of defective MMR. MSI observed in non-Hodgkin lymphomas was uniformly Type A, which implies that MMR deficiency occurs in this malignancy. Intriguingly, in non-Hodgkin lymphoma patients treated by CHOP/VEPA-based therapies, response to chemotherapy was significantly worse in those with microsatellite-unstable tumours (p = 0.027). As a consequence, the patient outcomes at 1 year after treatment were significantly less favourable in this population (p = 0.046), although the survival difference was not statistically confirmed in a longer term. These findings suggest that in some non-Hodgkin lymphomas MMR deficiency may lead to drug resistance in tumour cells and, consequently, to poor patient outcomes. In non-Hodgkin lymphoma, MSI may be a potential biomarker that predicts the tumour response against chemotherapy.     

Differences in genomic instability between intestinal- and diffuse-type gastric cancer

Background Microsatellite instability (MSI) and loss of heterozygosity (LOH) are lesions in the genome found with different frequencies in gastric carcinomas (GCAs). Despite a great body of studies, no systematic approach to the detailed classification of MSI and LOH in the two major types of GCA has been published. Methods Thirty-seven advanced GCAs, 25 intestinal-type (IGCAs) and 12 diffuse-type (DGCAs), were assayed with 15 autosomal tetranucleotide markers on 14 chromosomal arms. The observed frequencies and types of microsatellite alterations allowed stratification into subgroups, i.e., high- and low-grade MSI (MSI-H, MSI-L) or microsatellite-stable (MSS), and high- or low-grade, or non-detectable LOH (LOH-H, LOH-L, LOH-N). Results Collectively, the markers detected MSI-H tumors with sensitivity equal to that of BAT-26 (a single marker highly specific for MSI-H). Likewise, the markers detected LOH at chromosomal arms 5q, 18q, and 21q with a sensitivity equal to markers used previously. Seven (19%) MSI-H and six (16%) LOH-H tumors were found, with a significant association (P = 0.027) with IGCA: 92% of MSI-H and LOH-H occurred in IGCA patients only. Conversely, in DGCA, a significantly higher prevalence of a stable (LOH-N/MSS) phenotype was found as compared with IGCA (75.1% vs 28.0%; P = 0.035). The MSI-L phenotype was found in 57.9% of non-MSI-H IGCA tumors and was associated significantly (P = 0.015) with LOH-H. Conclusion A clear difference in genomic instability between IGCA and DGCA was found. In IGCA, the MSI and LOH pathways were more commonly involved, whereas in DGCA, a stable phenotype was predominant. As a novel finding, MSI-L as a true phenomenon and its association with LOH was observed in IGCA.     

Genomic instability and colon cancer

Colorectal cancer affected 135,000 people in the United States in 2001, resulting in 57,000 deaths. At the cellular level, colorectal cancer results from the progressive accumulation of genetic and epigenetic alterations that lead to the transformation of normal colonic epithelial cells to colon adenocarcinoma cells. The loss of genomic stability appears to be a key molecular and pathogenetic step that occurs early in the tumorigenesis process and serves to create a permissive environment for the occurrence of alterations in tumor suppressor genes and oncogenes. At least three forms of genomic instability have been identified in colon cancer: (1) microsatellite instability (MSI), (2) chromosome instability (i.e. aneusomy, gains and losses of chromosomal regions) (CIN), and (3) chromosomal translocations. Microsatellite instability occurs in 15% of colon cancers and results from inactivation of the mutation mismatch repair (MMR) system by either MMR gene mutations or hypermethylation of the MLH1 promoter. MSI promotes tumorigenesis through generating mutations in target genes that possess coding microsatellite repeats, such as TGFBR2 and BAX. CIN is found in the majority of colon cancers and leads to a different pattern of gene alterations that contribute to tumor formation. CIN appears to result primarily from deregulation of the DNA replication checkpoints and mitotic-spindle checkpoints. The mechanisms that induce and influence genomic instability in cancer in general and more specifically in colon cancer are only partly understood and are consequently under intense investigation. These studies have revealed mutation of the mitotic checkpoint regulators BUB1 and BUBR1 and amplification of STK15 in a subset of CIN colon cancers. The etiology of CIN in the other unexplained cases of colon cancer remains to be determined. Hopefully, discovery of the cause and specific role of genomic instability in colon cancer will yield more effective chemotherapy strategies that take advantage of this unique characteristic of cancer cells.     

Microsatellite instability in thorotrast-induced human intrahepatic cholangiocarcinoma

Thorotrast, a colloidal suspension of radioactive (232)ThO(2) that emits alpha particles, was used as a radiographic contrast during World War II. It is known to induce liver cancers, most frequently ICC, decades after injection. Since radiation induces genomic instability, we analyzed MSI in Thorotrast-induced ICC. The frequency of MSI(+) cases was 62.5% in Thorotrast ICC, whereas it was 22.7% in non-Thorotrast ICC. However, frameshift mutations of mononucleotide repeats were not observed in Thorotrast ICC. In addition, the MSI(+) phenotype was not associated with the quantity of Thorotrast deposited or the latency period of ICC induction. Promoter regions of both the hMLH1 and the hMSH2 MMR genes tended to be hypermethylated in the tumor part compared to the adjacent nontumor part in Thorotrast ICC. Methylation of the hMLH1 promoter was associated with the MSI(+) phenotype in Thorotrast ICC. In contrast, methylation status of these promoter regions was not related to MSI in non-Thorotrast ICC cases. These findings suggest that MSI induced by exposure to Thorotrast mainly reflects clonal expansion of cancer cells and is partly due to inactivation of hMLH1 by hypermethylation.