错配修复基因与大肠癌相关性的研究进展

ＤＮＡ错配修复（ｍｉｓｍａｔｃｈｒｅｐａｉｒ,ＭＭＲ）是机体内ＤＮＡ修复机制的一种重要形式,广泛存在于生物体中,在防止基因突变和维持基因组稳定性的过程中起关键作用。最早研究发现错配修复基因突变与遗传性非息肉性大肠癌的发生有密切关联。越来越多的研究发现,错配修复基因功能缺失在一部分散发性大肠癌的发生过程中也起到一定的作用。本文就错配修复基因与大肠癌相关性的研究进展作一综述。     

错配修复基因异常改变与大肠癌的关系

研究表明，大肠癌(colorectal cancer，CRC)的发生是1个多因素多步骤的过程，是机体的内因与环境的外因相互作用的结果。其中错配修复基因的改变与遗传性和散发性结直肠癌的基因不稳定性有关。本文就错配修复基因异常导致大肠癌的机制及其诊断与治疗的最新研究进展做一综述。     

错配修复基因变异与中国人散发性大肠癌发病年龄之间的关系

目的 :探讨错配修复基因变异与中国人散发性大肠癌发病年龄之间的关系。方法 :随机选取 1 0 0例临床初诊的散发性大肠癌患者 ,配对提取手术切除的癌组织和同源正常组织的基因组DNA ,检测并分析癌细胞微卫星DNA不稳定性 (MSI)。结果 :46/1 0 0 (46 % )的癌组织MSI阳性 (MSI+ ) ,其中 1 8%为MSI+ H ,2 8%MSI+ L。按年龄分组分析表明 ,发病年龄 <45岁的大肠癌患者中MSI+ 检出率明显高于≥ 65岁的大肠癌患者 (P <0 .0 5) ,且MSI+ 的检出率与患者的发病年龄呈负相关 (r =- 0 .95 ,P <0 .0 5) ,但与癌细胞的分化及患者的临床分期无关。结论 :中国人散发性大肠癌中错配修复基因功能的丧失可能出现在癌症发生的早期 ,可能参与构成部分散发性大肠癌发病的遗传背景因素     

散发性大肠癌的错配修复缺陷研究

目的探讨错配修复缺陷的散发性大肠癌的临床病理特征及错配修复缺陷检测手段的应用。方法对71例散发性大肠癌行hMLH1启动子甲基化检测、微卫星不稳定检测以及hMLH1和hMSH2的免疫组化检测,分析错配修复缺陷的散发性大肠癌的临床病理特征,探讨三种检测方法的应用价值。结果hMLH1基因启动子甲基化、微卫星不稳定和错配修复蛋白表达的阳性率分别为9.9%,9.9%和71.0%,三者密切相关。hMLH1启动子甲基化和微卫星不稳定的散发性大肠癌均具有结肠癌多发和低分化腺癌相对多见的特征。错配修复蛋白表达阴性的散发性大肠癌仅具有低分化腺癌相对多见的特征。结论错配修复缺陷的散发性大肠癌具有结肠癌和低分化腺癌多发的倾向,hMLH1启动子甲基化和微卫星不稳定以及错配修复蛋白的失表达三者密切相关。     

DNA错配修复系统缺陷在结肠癌中的研究进展

结肠癌在其多阶段演变过程中涉及多种基因。约85％的结肠癌由染色体不稳定（chromosomalinsta-bility,CIN）引起,另有约15％的结肠癌则由DNA错配修复（mismatchrepair,MMR）基因缺陷所致,其中遗传性非息肉性结直肠癌（hereditarynonpolypo—siscolorectalcancer,HNPCC）占3％～5％,而散发性结肠癌占10％～15％。     

DNA错配修复基因与肿瘤研究新进展

DNA错配修复(mismatch repair,MMR)基因对维持基因组的稳定性有重要作用,MMR基因突变与肿瘤的发生、发展关系密切.近年来,MMR基因在肿瘤组织中的作用成为研究热点,本文就其新进展作一简要综述.     

肺癌组织中错配修复基因mRNA表达

目的 探讨ＤＮＡ错配修复（ＭＭＲ）基因ｍＲＮＡ在肺癌组织中冢其与微卫星６改变关系。方法 用ＲＴ－ＰＣＲ和ＰＣＲ－变性聚丙烯酰胺凝胶电泳－银染法,检测４６原发性肺癌组织中５种ＭＭＲ基因ｍＲＮＡ表达及６种微卫星改变。结果 ５种ＭＭＲ基因ｍＲＮＡ在肺癌组织中表达降你的发生庇为１３．０％～３２．６％,至少一种基因ｍＲＮＡ表达降爸的发生率为５８．７％（２７／４６）。３９．１％（１８／４６）病例有至少２种基因     

微卫星不稳定性与结肠癌的研究进展

近年来的研究表明,微卫星不稳定性(MI)尤其是高度微卫星不稳定性(MI-H)与许多肿瘤的发生和发展关系密切.本文就MI的发生和致瘤机制、临床病理学意义以及MI相关研究存在问题等方面的研究现状作一综述.     

肺癌微卫星不稳定性与错配修复基因缺陷的相关性研究

 目的　通过对肺癌微卫星不稳定性（MSI）的分析与错配修复基因蛋白表达的检测,探讨肺癌发病的分子机制。方法　从50例肺癌患者的正常肺组织、癌组织中提取DNA;SSCP法检测标本中MSI发生情况;免疫组织化学法检测错配修复基因hMLH1及hMSH2在肺癌中的表达情况。结果　50例肺癌中微卫星高度不稳定（MSI-H）14例,低度不稳定（MSI-I）21 例,稳定（MSS）15例,正常组织中未出现MSI,两者之间差异有统计学意义（P＝0.000）;免疫组化结果显示hMLH1在MSI肺癌组织中常为缺失表达,表达率为74 %（37／50）;hMSH2在MSI肺癌组织中也呈缺失表达,表达率为32 %（16／50）;而在MSS肺癌组织中均显示hMLH1、 hMSH2基因蛋白表达阳性。结论　肺癌的发生可能存在MSI途径,而hMLH1、hMSH2的表达失活则可能导致MSI的发生,因此,MSI可作为肺癌诊断的指标之一。     

肺癌微卫星不稳定性与错配修复基因缺陷的相关性研究

目的 通过对肺癌微卫星不稳定性(MSI)的分析与错配修复基因蛋白表达的检测,探讨肺癌发病的分子机制.方法 从50例肺癌患者的正常肺组织、癌组织中提取DNA;SSCP法检测标本中MSI发生情况;免疫组织化学法检测错配修复基因hMLH1及hMSH2在肺癌中的表达情况.结果 50例肺癌中微卫星高度不稳定(MSI-H)14例,低度不稳定(MSI-I)21例,稳定(MSS)15例,正常组织中未出现MSI,两者之间差异有统计学意义(P=0.000);免疫组化结果显示hMLH1在MSI肺癌组织中常为缺失表达,表达率为74%(37/50);hMSH2在MSI肺癌组织中也呈缺失表达,表达率为32%(16/50);而在MSS肺癌组织中均显示hMLH1、hMSH2基因蛋白表达阳性.结论 肺癌的发生可能存在MSI途径,而hMLH1、hMSH2的表达失活则可能导致MSI的发生,因此,MSI可作为肺癌诊断的指标之一.     

筛查结直肠癌DNA错配修复基因缺失的方法分析

目的:通过对筛查结直肠癌DNA错配修复(mismatch repair,MMR)基因缺失两种最常用的检测方法的分析,寻找更为经济有效的检测策略。方法:分析新疆医科大学第一附属医院2018年9月至2019年9月收治并行手术的结直肠癌患者的肿瘤组织223例,采用免疫组织化学法检测平台检测MLH1、MSH2、PMS2、MSH6的表达缺失情况,PCR-毛细管电泳法检测肿瘤微卫星不稳定(microstatellites instability,MSI)状态。结果:在223例结直肠癌中,27例(12.1%)MMR蛋白表达缺失(MMR deficiency,dMMR),196例(87.9%)MMR蛋白表达完整(MMR proficient,pMMR)。MLH1、MSH2、MSH6和PMS2的缺失率分别为9.0%(20/223)、1.8%(4/223)、2.7%(6/223)和9.4%(21/223)。包含PMS2和MSH6的2种抗体试验筛查dMMR结直肠癌的灵敏度和特异度与4种抗体试验(MLH1、MSH2、PMS2、MSH6)的灵敏度和特异度均相同。微卫星高度不稳定(MSI-high,MSI-H)2...     

Mismatch repair status in patients with primary operable colorectal cancer: associations with the local and systemic tumour environment

Background:

Mismatch repair-deficient (dMMR) colorectal cancer (CRC) is associated with a conspicuous local immune infiltrate; however, its relationship with systemic inflammatory responses remains to be determined. The present study aims to examine the relationships and prognostic value of assessment of the local and systemic environment in the context of MMR status in patients with CRC.

Methods:

The relationship between MMR status, determined using immunohistochemistry, and the local inflammatory cell infiltrate, differential white cell count, neutrophil : platelet score (NPS), neutrophil : lymphocyte ratio and modified Glasgow Prognostic Score (mGPS), and cancer-specific survival was examined in 228 patients undergoing resection of stage I–III CRC.

Results:

Thirty-five patients (15%) had dMMR CRC. Mismatch repair deficiency was associated with a higher density of CD3⁺, CD8⁺ and CD45R0⁺ T lymphocytes within the cancer cell nests and an elevated mGPS (mGPS2: 23% vs 9%, P=0.007) and NPS (NPS2: 19% vs 3%, P=0.001). CD3⁺ density (P<0.001), mGPS (P=0.01) and NPS (P=0.042) were associated with survival independent of MMR status (P=0.367) and stratified 5-year survival of patients with MMR-competent CRC from 94% to 67%, 83% to 46% and 78% to 60% respectively.

Conclusions:

Mismatch repair deficiency was associated with local and systemic environments, and in comparison with their assessment, dMMR had relatively poor prognostic value in patients with primary operable CRC. In addition to MMR status, local and systemic inflammatory responses should be assessed in these patients.     

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.     

Familial microsatellite-stable non-polyposis colorectal cancer: Incidence and characteristics in a clinic-based population

Background:About 15%–20% of colorectalcancers (CRCs) are familial. While a fraction of these arise in thecontext of hereditary syndromes, the causes underlying the majority offamilial CRCs are not yet understood. Patients and methods:Family history of cancer, clinicalcharacteristics, and microsatellite instability (MSI) in a series of 100consecutive CRC patients were evaluated. Results:Eighteen patients had a positive family history ofCRC in a first-degree relative. Of these, two had a clinical diagnosisof familial adenomatous polyposis (FAP), and three were diagnosed withhereditary non-polyposis colorectal cancer (HNPCC) following results ofMSI analysis. A diagnosis of HNPCC was also established in a fourthpatient with early onset CRC, who had a second-degree relative with CRC,and whose tumor was positive for MSI. The remaining 13 familial CRCs didnot show MSI in tumor DNA. The mean age at tumor diagnosis in patientswith familial microsatellite-stable (MSS) CRC was higher than in HNPCCand FAP patients and similar to that recorded in sporadic cases. Theincidence of second primary malignancies was significantly higher infamilial MSS CRC probands (n = 4) compared to patients whodid not have a diagnosis of FAP or HNPCC and did not have first-degreerelatives affected with CRC (n = 6, in a total of 81probands with these characteristics). Conclusions:These results define the existence of a subsetof familial CRCs characterized by relatively late age at onset, highincidence of second primary tumors, and absence of MSI in tumor DNA.     

Clinicopathological significance of microsatellite instability and mutated RIZ in colorectal cancer.

BACKGROUND: Several studies have shown that microsatellite instability (MSI) is related to favourable survival in colorectal cancer patients but there are controversial results. Tumour suppressor gene RIZ is a susceptible mutational target of MSI. However, its clinicopathological significance has not been investigated. We investigated the prognostic significance of MSI in Swedish colorectal cancer patients and the clinicopathological significance of RIZ mutations. PATIENTS AND METHODS: We analysed 438 colorectal adenocarcinomas for MSI by microsatellite analysis. Among them, 29 MSI and 28 microsatellite stable (MSS) tumours were examined for RIZ mutations by DNA sequencing. RESULTS: MSI (13% of 438 cases) was not associated with survival (rate ratio = 0.97, 95% confidence interval = 0.57-1.64, P = 0.90), although it was related to proximal tumour (P <0.001), poor differentiation and mucinous carcinomas (P <0.001), multiple tumours (P = 0.01) and negative/weak expression of hMLH1 (P = 0.03). RIZ mutations were detected in 31% of 29 MSI tumours but in none of the 28 MSS tumours. The mutations were related to female (P = 0.01), proximal tumour (P = 0.01), stage B (P = 0.01) and poor differentiation (P = 0.047). CONCLUSIONS: MSI was not a prognostic factor in the Swedish patients included in this study. Clinicopathological variables associated with RIZ mutations might be a consequence of the MSI characteristics.     

Candidate driver genes in microsatellite-unstable colorectal cancer

Defects in the mismatch repair system lead to microsatellite instability (MSI), a feature observed in ～ 15% of all colorectal cancers (CRCs). Microsatellite mutations that drive tumourigenesis, typically inactivation of tumour suppressors, are selected for and are frequently detected in MSI cancers. Here, we evaluated somatic mutations in microsatellite repeats of 790 genes chosen based on reduced expression in MSI CRC and existence of a coding mononucleotide repeat of 6-10 bp in length. All the repeats were initially sequenced in 30 primary MSI CRC samples and whenever frameshift mutations were identified in >20%, additional 70 samples were sequenced. To distinguish driver mutations from passengers, we similarly analyzed the occurrence of frameshift mutations in 121 intronic control repeats and utilized a statistical regression model to determine cut-off mutation frequencies for repeats of all types (A/T and C/G, 6-10 bp). Along with several know target genes, including TGFBR2, ACVR2, and MSH3, six novel candidate driver genes emerged that harbored significantly more mutations than identical control repeats. The mutation frequencies in 100 MSI CRC samples were 51% in G8 of GLYR1, 47% in T9 of ABCC5, 43% in G8 of WDTC1, 33% in A8 of ROCK1, 30% in T8 of OR51E2, and 28% in A8 of TCEB3. Immunohistochemical staining of GLYR1 revealed defective protein expression in tumors carrying biallelic mutations, supporting a loss of function hypothesis. This is a large scale, unbiased effort to identify genes that when mutated are likely to contribute to MSI CRC development.     

Microsatellite instability in colorectal cancer

Approximately 20 percent of right-sided colon cancers and 5 percent of left-sided colon and rectal cancers have a deficient DNA mismatch repair system. This results in the widespread accumulation of mutations to nucleotide repeats, some of which occur within the coding regions of cancer-related genes such as TGFβRII and BAX. A standardized definition for microsatellite instability (MSI) based on the presence of deletions to mononucleotide repeats is gaining widespread acceptance in both research and the clinic. Colorectal cancer (CRC) with MSI are characterized histologically by an abundance of tumor-infiltrating lymphocytes, poor differentiation and a signet ring or mucinous phenotype. In younger patients these tumors usually develop along the chromosomal instability pathway, in which case the mismatch repair genes are inactivated by germline mutation, somatic mutation and loss of heterozygosity. In older patients MSI CRC usually develops against a background of widespread hypermethylation that includes methylation-induced silencing of the mismatch repair gene MLH1. The overall biological and clinical phenotype of MSI CRC that arise in these two pathways is likely to be different and may account for some of the discordant results reported in the literature relating to the clinical properties of these tumors. The available evidence indicates that MSI is unlikely to be a clinically useful marker for the prognostic stratification of early-stage CRC. The predictive value of MSI for response to 5-fluorouracil-based chemotherapy remains controversial, while for other agents the predictive value is difficult to assess because they are used in combination regimens. The MSI phenotype is being actively investigated for novel therapeutic approaches based on the principle of synthetic lethality. Finally, the MSI status of CRC is an extremely useful marker for population-based screening programs that aim to identify individuals and families with the hereditary cancer condition known as Lynch syndrome.     

Prognosis and chemosensitivity of deficient MMR phenotype in patients with metastatic colorectal cancer: An AGEO retrospective multicenter study

Mismatch repair-deficient (dMMR) and/or microsatellite instability-high (MSI) colorectal cancers (CRC) represent about 5% of metastatic CRC (mCRC). Prognosis and chemosensitivity of dMMR/MSI mCRC remain unclear. This multicenter study included consecutive patients with dMMR/MSI mCRC from 2007 to 2017. The primary endpoint was the progression-free survival (PFS) in a population receiving first-line chemotherapy. Associations between chemotherapy regimen and survival were evaluated using a Cox regression model and inverse of probability of treatment weighting (IPTW) methodology in order to limit potential biases. Overall, 342 patients with dMMR/MSI mCRC were included. Median PFS and overall survival (OS) on first-line chemotherapy were 6.0 and 26.3 months, respectively. For second-line chemotherapy, median PFS and OS were 4.4 and 21.6 months. Longer PFS (8.1 vs. 5.4 months, p = 0.0405) and OS (35.1 vs. 24.4 months, p = 0.0747) were observed for irinotecan-based chemotherapy compared to oxaliplatin-based chemotherapy. The association was no longer statistically significant using IPTW methodology. In multivariable analysis, anti-VEGF as compared to anti-EGFR was associated with a trend to longer OS (HR = 1.78, 95% CI 1.00–3.19, p = 0.0518), whatever the backbone chemotherapy used. Our study shows that dMMR/MSI mCRC patients experienced short PFS with first-line chemotherapy with or without targeted therapy. OS was not different according to the chemotherapy regimen used, but a trend to better OS was observed with anti-VEGF. Our study provides some historical results concerning chemotherapy in dMMR/MSI mCRC in light of the recent nonrandomized trials with immune checkpoint inhibitors.