散发性结直肠癌微卫星不稳定状态与错配修复蛋白表达缺失及临床病理特征的相关性

目的： 探讨散发性结直肠癌微卫星不稳定(microsatellite instability,MSI)情况及其与错配修复 (mismatch repair,MMR) 蛋白MLH1、MSH2、MSH6、PMS2表达缺失的相关性,并总结MSI散发性结直肠癌的临床病理学特征。方法：多重荧光PCR法检测散发性结直肠癌肿瘤组织DNA的微卫星不稳定性,免疫组化(Immunohistochemistry,IHC)S-P法检测散发性结直肠癌肿瘤组织MLH1、MSH2、MSH6、PMS2蛋白的表达缺失,分析MSI发生与MMR蛋白表达缺失及临床病理特征的相关性。结果：75 例散发性结直肠癌检出MSI 21例(28%),包括 MSI-H 19例、MSI-L 2例,其他54例(72%)为MSS。检出MMR蛋白表达缺失16例(21.33%),其中15例(93.75%)为MSI-H、1例(6.25%)为MSS;MMR蛋白表达59例(78.67%),其中4例(6.78%)为MSI-H、2例(3.39%)MSI-L,其他53例为MSS。MSI组MMR蛋白缺失率(15/21,71.43%)显著高于MSS组(1/54,1.9%)（P<0.01）。MSI与患者年龄,是否黏液腺癌,肿瘤有无远处转移有关（P<0.01）,其中MSI-H好发于年龄>50岁、肿瘤无远处转移、MMR蛋白缺失人群,且类型以黏液腺癌为主。结论： 散发性结直肠癌肿瘤组织中MSI发生率高于MMR蛋白缺失率,并且MSI-H的散发性结直肠癌转移风险较低、预后较好。检测MSI 状态对提高结直肠癌的预防、诊断和治疗水平,降低结直肠癌的发病率和病死率有着重要意义。     

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...     

DNA错配修复蛋白表达与胃腺癌临床病理特征的关系及意义

目的:检测DNA错配修复（mismatch repair，MMR）主要蛋白（MLH1、MSH2、MSH6和PMS2)在人胃腺癌组织中的表达，并分析错配修复缺陷（defective mismatch repair，dMMR）与胃腺癌临床病理因素及预后的关系。方法:采用免疫组织化学染色法检测4种MMR蛋白（MLH1、MSH2、MSH6和PMS2)在120例人胃腺癌组织中的表达，并从癌症基因组图谱（The Cancer Genome Atlas，TCGA）公共数据库下载432例胃腺癌患者的临床病理资料和微卫星不稳定性（microsatellite instability，MSI）的检测结果，分析MSI与胃腺癌临床病理特征的关系，利用TCGA的数据分析高频度微卫星不稳定（MSI-H）与胃腺癌患者预后的关系。结果:免疫组化染色结果显示在120例胃腺癌组织中，MMR蛋白表达正常（pMMR）组106例（88.3%），MMR蛋白表达缺失（dMMR)组14例（11.7%），其中MLH1缺失2例（1.7%）、PMS2缺失13例（10.8%）、MLH1和PMS2共同缺失2例（1.7%）、MSH2和MSH6共同缺失1例（0.8%）。统计分析结果显示，dMMR与胃腺癌淋巴结转移相关（P=0.022），而与其他临床病理因素无关。TCGA数据统计分析结果显示，MSI-H与胃腺癌患者年龄（P=0.001)、性别（P=0.000)、原发肿瘤部位（P=0.000)、Lauren分型（P=0.011）、肿瘤浸润深度T分期（P=0.024)、淋巴结有无转移（P=0.008)有关。Kaplan-Meier生存分析结果显示MSI-H型胃腺癌患者有预后更好的趋势，但差异不具有统计学意义（P=0.070）。结论:120例中国胃腺癌患者中MSI/dMMR型胃腺癌占比为11.7%，且dMMR状态与胃腺癌的淋巴结转移呈负相关；MSI-H型胃腺癌患者具有年龄大、多为女性、肿瘤多位于胃远端、肿瘤浸润深度T分期低、无淋巴结转移的特征，且MSI-H型胃腺癌具有预后更好的趋势，但不具有统计学意义。MSI状态与胃癌预后的关系尚需进一步深入研究和大样本数据的验证。     

胃癌组织中p53蛋白表达和微卫星不稳定及其与预后的相关性研究

摘 要：［目的］ 探讨胃癌组织中 p53 蛋白表达与微卫星不稳定(microsatellite instability,MSI)与胃癌临床病理特征及预后的关系。［方法］ 选取行胃癌手术患者104例,采用免疫组织化学法检测肿瘤组织中p53蛋白和错配修复蛋白(mismatch repair protein,MMRP)（MLH1、MSH2、MSH6和PMS2）表达,分析p53表达和MSI与患者临床病理参数的关系。术后患者随访2年,采用Logistics回归分析影响患者预后的危险因素。［结果］ 胃癌组织中p53、MLH1、MSH2、MSH6和PMS2均定位于肿瘤细胞核。104例胃癌中p53阳性46例(44.23%);MMRP阳性65例(62.50%),39例MMRP表达缺失(37.50%),其中MLH1、MSH2、MSH62及PMS表达缺失分别为25例(24.04%)、19例(18.27%)、18例(17.31%)和 22例(21.15%)。胃癌低分化组及Ⅲ期组中p53阳性表达率显著降低(P<0.05)。p53在癌组织中的表达与MSI呈负相关(r=-0.486,P<0.05)。Logistic多因素回归分析显示,TNM分期、MSI和p53阴性是影响患者预后的独立危险因素。［结论］ 胃癌组织中p53与MSI呈负相关。对胃癌组织监测p53与MSI对制定给药方案及评估预后具有重要意义。     

MMR蛋白在515例子宫内膜样腺癌中表达及其与临床病理学特征的相关性分析

背景与目的：林奇综合征（Lynch syndrome,LS）相关的子宫内膜癌有着独特的临床病理学特征及治疗手段。对新发子宫内膜癌患者采用免疫组织化学（immunohistochemistry,IHC）染色的方法检测错配修复（mismatch repair,MMR）蛋白表达情况,可以有效地筛查LS相关的癌症患者。本研究探讨MMR蛋白（MLH1、MSH2、MSH6及PMS2）在子宫内膜样腺癌中的表达情况及其与患者临床病理学特征的关系。方法：收集中国医科大学盛京医院2018年1月—2020年8月共515例子宫内膜样腺癌连续性病例为研究对象,年龄范围为28 ~ 81（57.73±8.41）岁。采用IHC染色的方法检测癌组织中MLH1、MSH2、MSH6和PMS2蛋白表达情况,应用聚合酶链式反应（polymerase chain reaction,PCR）方法对MLH1蛋白表达缺失的标本进行基因的甲基化检测,并且分析MMR蛋白表达缺失情况与子宫内膜样腺癌临床病理学特征的关系。只要有一种MMR蛋白表达缺失即判定为MMR蛋白错配修复缺陷（deficient mismatch repair,dMMR）,蛋白全部阳性则判定为MMR表达完整（proficient mismatch repair,pMMR）。结果：515例子宫内膜样腺癌中有138例（26.8%）发生MMR蛋白表达缺失,MLH1、PMS2、MSH2及MSH6蛋白表达缺失率分别是16.3%（84/515）、19.0%（98/515）、5.4%（28/515）、8.0%（41/515）。MMR蛋白的缺失以MLH1和PMS2联合表达缺失（60.9%,84/138）为主;其次为MSH2和MSH6联合表达缺失（18.8%,26/138）;MSH2、MSH6和PMS2联合表达缺失有2例（1.4%,2/138）;PMS2、MSH2和MSH6蛋白单独表达缺失比例分别为8.0%（11/138）、1.4%（2/138）、10.1%（14/138）。对27例MLH1蛋白表达缺失标本进行甲基化检测,结果显示,阳性率为85.2%（23/27）。515例子宫内膜样腺癌组织中的MMR蛋白表达缺失与患者发病年龄、国际妇产科联合会（The International Federation of Gynecology and Obstetrics,FIGO）分期、组织学分化程度、浸润深度、脉管转移、神经侵犯、淋巴结转移、p53异常表达、肿瘤浸润淋巴细胞（tumor infiltrating lymphocyte,TIL）及肿瘤伴瘤周淋巴细胞有相关性,而与是否累及子宫下段无关。与pMMR的患者相比,dMMR的患者发病年龄更小,FIGO临床分期多为Ⅲ ~ Ⅳ期,组织学分化程度多为低分化,肿瘤多无肌层浸润,肿瘤多出现脉管神经侵犯及淋巴结转移,肿瘤浸润淋巴细胞增多,且肿瘤伴瘤周淋巴细胞更显著,MSH6蛋白缺失患者多无p53异常表达。结论：dMMR的子宫内膜样腺癌患者具有独特的临床病理学特征。应用免疫组织化学染色方法检测MMR蛋白表达情况,并对MLH1表达缺失的标本进行基因甲基化检测,能初步筛查LS患者,对肿瘤患者免疫治疗具有一定指导意义。     

非小细胞肺癌组织微卫星不稳定与T淋巴细胞浸润的关系

目的:分析非小细胞肺癌(non-small cell lung cancer,NSCLC)组织错配修复蛋白MLH1、MSH2和MSH6的表达和T淋巴细胞浸润情况,探讨微卫星不稳定(microsatellite instability,MSU与NSCLC组织T淋巴细胞浸润的关系.方法:收集天津医科大学肿瘤医院2004年至2010年NSCLC组织标本100例,应用免疫组化法检测癌组织中MLH1、MSH2和MSH6的表达,以其中1种及1种以上蛋白表达阴性者判定为MSI;同时检测T淋巴细胞浸润情况,并分析MSI与NSCLC临床病理特征的关系.结果:NSCLC组织中MSI检出率24％,少于微卫星稳定(microsatellite stability,MSS).MSI NSCLC组织中T淋巴细胞浸润明显高于MSS者.免疫组化结果显示:MSI NSCLC组织CD3+、CD4+、CD8+T淋巴细胞浸润数目明显多于MSS NSCLC 组织,两者差异有统计学意义(P＜0.05).MSI与患者的年龄有关(P＜0.05),而与患者的性别、肿瘤组织类型、肿瘤大小、淋巴结有无转移和肿瘤有无远处转移均无关(P＞0.05).结论:MSI影响NSCLC肿瘤免疫微环境,MSI的检测可为NSCLC免疫治疗效应提供预测指标.     

免疫组织化学与聚合酶链反应在结肠癌微卫星状态筛选中的比较

目的 比较免疫组织化学（IHC）与聚合酶链反应（PCR）检测结肠癌微卫星不稳定状态的一致性,评价IHC检测微卫星不稳定状态的可行性。方法 采用IHC和PCR两种方法分别检测80例结肠癌中微卫星不稳定状态。结果 （1）IHC法检测结果显示癌旁正常黏膜中错配修复蛋白（包括MLH1、PMS2、MSH2、MSH6）均阳性表达。四个蛋白表达缺失率分别为23.8%（19/80）、21.2%（17/80）、7.5%（6/80）、3.7%（3/80）,其中有16例显示MLH1、PMS2表达同时缺失,3例显示MSH2和MSH6表达同时缺失。19例（23.8%）显示为高频微卫星不稳定,剩余病例显示微卫星稳定状态或低频微卫星不稳定;（2）PCR产物测序结果显示18例为高频微卫星不稳定,5例为低频微卫星不稳定,其余病例均为微卫星稳定状态;（3）两种方法具有高度一致性。结论 与PCR法相比,IHC具有操作简单、耗时短、费用低以及对实验仪器条件要求不高等优点,具有较高的临床应用价值,可以作为检测结肠癌微卫星不稳定状态的首选方法。     

错配修复基因蛋白在结直肠癌诊治中的临床应用

  目的  探讨错配修复基因（mismatch repair gene,MMR）蛋白MLH1、MSH2、MSH6、PMS2在结直肠癌中的表达及在临床中的应用。  方法  选取四川省人民医院2015年1月至2016年9月收治的607例结直肠癌患者,采用免疫组织化学法检测手术标本中MMR蛋白的表达情况,研究其与临床病理学的关系,并评价其在Lynch综合征和散发性结直肠癌筛查中的价值。  结果  607例患者中MMR表达缺失率为35.58%。MMR蛋白表达缺失的阴性组与表达正常的阳性组,在年龄、性别、肿瘤大小、P53、CD34、D2-40的比较,差异均无统计学意义（P>0.05）;两组患者在肿瘤位置、分化程度、TNM分期、淋巴结转移、VEGF、Ki-67的比较,差异均有统计学意义（P < 0.05）。联合检测MLH1、MSH2、PSM2、MSH6蛋白可以作为初步筛选Lynch综合征患者的方法。  结论  对结直肠癌患者的手术标本进行MMR检测,筛查Lynch综合征患者和家族成员,进行管理及干预,可降低部分人群患结直肠癌的风险。      

MMR蛋白在云南地区遗传性非息肉病性 大肠癌中的表达及意义

 目的探讨MLH1、MSH2、PMS2和MSH6蛋白在云南地区遗传性非息肉病性大肠癌（hereditary nonpolyposis colorectal cancer,HNPCC）中的表达及意义。方法根据目前国内外通常采用的三个标准在 云南地区选择遗传性非息肉病性大肠癌病例13个家系中19例肿瘤组织,应用免疫组织化学方法（IHC）检 测MLH1、MSH2、PMS2和MSH6蛋白。结果在这13个家系中,MLH1、MSH2、PMS2和MSH6四种蛋白表达缺失率分 别为30.77%、38.46%、23.08%、15.38%,其中2例家系先证者同时存在MLH1和PMS2蛋白表达缺失,2例家系 先证者同时存在MSH2和MSH6蛋白表达缺失,四种MMR蛋白总的表达缺失率为84.62%。结论云南地区HNPCC病 例存在MLH1、MSH2、PMS2和MSH6 四种MMR蛋白不同程度的缺失表达,应用IHC检测MMR蛋白可以作为筛选 HNPCC家系的一有效手段。     

MLH1基因突变在Lynch综合征中的研究进展

结直肠癌是常见的消化系统恶性肿瘤,有些类型具有家族聚集性。Lynch综合征作为最常见的遗传性结直肠癌综合征,主要因相关基因突变致错配修复蛋白表达异常、减少或缺失而致病,其主要包括MLH1、MSH2、MSH6和PMS2基因。考虑到MLH1和MSH2基因的胚系突变占Lynch综合征总突变近90%,因此本文将着重综述近年来错配修复蛋白基因MLH1的突变,整理在不同国家和地区的重要创始人突变。通过对公共数据库已有报道突变及单中心收录数据比较,从而对其诊断,基因筛查,为了解不同人种和地域的Lynch综合征创始人突变提供一定的指导意义。     

Immunohistochemical expression pattern of MMR protein can specifically identify patients with colorectal cancer microsatellite instability

The microsatellite instability (MSI) pathway is found in most cases of hereditary nonpolyposis colorectal cancer (HNPCC) and in 12 % of sporadic colorectal cancer (CRC). It involves inactivation of deoxyribonucleic acid mismatch repair (MMR) genes MLH1, MSH2, PMS2, and MSH6. MMR germline mutation detections are an important supplement to HNPCC clinical diagnosis. It enables at-risk and mutation-positive relatives to be informed about their cancer risks and to benefit from intensive surveillance programs that have been proven to reduce the incidence of CRC. In this study, we analyzed for the first time in Tunisia the potential value of immunohistochemical assessment of MMR protein to identify microsatellite instability in CRC. We evaluate by immunohistochemistry MMR protein expression loss in tumoral tissue compared to positive expression in normal mucosa. Immunohistochemistry revealed loss of expression for MLH1, MSH2, MSH6, and PMS2 in 15, 21, 13, and 15 % of cases, respectively. Here, we report a more elevated frequency of MSI compared to data of the literature. In fact, by immunohistochemistry, 70 % of cases were shown to be MSS phenotype, whereas 30 % of cases, in our set, were instable. Moreover, according to molecular investigation, 71 % of cases were instable (MSI-H) and remaining cases were stable (29 %). Thus, we found a perfect association between MMR immunohistochemical analyses and MSI molecular investigation. Immunohistochemical analysis of MMR gene product expression may allow one to specifically identify MSI phenotype of patients with colorectal carcinomas.     

The added value of PMS2 immunostaining in the diagnosis of hereditary nonpolyposis colorectal cancer

Identification and characterization of the genetic background in patients with the hereditary nonpolyposis colorectal cancer (HNPCC) syndrome is important since control programmes can in a cost-effective manner prevent cancer development in high-risk individuals. HNPCC is caused by germline mismatch repair (MMR) gene mutations and the genetic analysis of HNPCC therefore includes assessment of microsatellite instability (MSI) and immunohistochemical MMR protein expression in the tumor tissue. MSI is found in >95% of the HNPCC-associated tumors and immunostaining using antibodies against the MMR proteins MLH1, MSH2, and MSH6 has been found to correctly pinpoint the affected gene in about 90% of the cases. The PMS2 antibody was the most recently developed and we have in a clinical material assessed the added value of PMS2 immunostaining in 213 patients with suspected hereditary colorectal cancer. All 119 MSS tumors showed retained expression for all four antibodies and PMS2 did thus not identify any underlying MMR defect in these cases. However, PMS2 immunostaining contributed to the characterization of the MMR defect in a subset of the MSI tumors. Concomitant loss of MLH1 and PMS2, which functionally interact in the MutLα complex, was found in 98% of the tumors from patients with germline MLH1 mutations. Among the 12 MSI-high tumors with retained expression of MLH1, MSH2 and MSH6, 8 tumors showed loss of PMS2 staining, and mutations in MLH1 were identified in 2 and mutations in PMS2 in 3 of these individuals. In summary, isolated loss of PMS2 was found in 8% of the MSI-high tumors in our series, including 8/12 previously unexplained MSI-high tumors, in which mutations either in MLH1 or in PMS2 were identified in five cases.     

Microsatellite instability and expression of MLH1 and MSH2 in carcinomas of the small intestine

BACKGROUND: Carcinomas of the small intestine are rare, but the risk is greatly increased in patients with hereditary nonpolyposis colorectal cancer (HNPCC) due to an inherited mismatch repair (MMR) gene mutation, most commonly affecting the genes MLH1 or MSH2. Defective MMR is characterized by microsatellite instability (MSI) and loss of MMR protein expression in the tumor tissue. However, a subset of several sporadic tumor types, including about 15% of colon cancers, also evolve through defective MMR. METHODS: The authors have assessed the frequency of MSI and analyzed the immunohistochemical expression of MLH1 and MSH2 in a population-based series of 89 adenocarcinomas of the small intestine. To study the contribution of MSI and defective MMR protein expression in young patients, 43 cancers of the small intestine from patients below age 60 years (including 24 tumors from the population-based series and an additional 19 tumors from young individuals) were also analyzed. RESULTS: MSI was detected in 16/89 tumors (18%) in the population-based series, and immunohistochemistry revealed loss of expression for MLH1 in 7/16 MSI tumors and in 2/73 MSS tumors, whereas all tumors showed normal expression for MSH2. Among the young patients, the authors identified MSI in 10/43 tumors (23%), and 6 of these 10 MSI tumors showed immunohistochemical loss of MMR protein expression, which affected MLH1 in 3 cases and MSH2 in 3 cases. CONCLUSIONS: The frequency of MSI (18%) in adenocarcinomas of the small intestine equals that of colon cancer. However, silencing of MLH1 seems to explain the MSI status in only about half of the MSI tumors. Among patients with cancer of the small intestine before age 60 years, MSI is found in 23% of the cases, with MLH1 and MSH2 being affected at equal frequencies, indicating that HNPCC may underly a subset of such cases.     

Relationship between MLH1, PMS2, MSH2 and MSH6 gene-specific alterations and tumor mutational burden in 1057 microsatellite instability-high solid tumors

Microsatellite instability-high (MSI-H) and tumor mutational burden (TMB) are predictive biomarkers for immune-checkpoint inhibitors (ICIs). Still, the relationship between the underlying cause(s) of MSI and TMB in tumors remains poorly defined. We investigated associations of TMB to mismatch repair (MMR) protein expression patterns by immunohistochemistry (IHC) and MMR mutations in a diverse sample of tumors. Hypothesized differences were identified by the protein/gene affected/mutated and the tumor histology/primary site. Overall, 1057 MSI-H tumors were identified from the 32 932 tested. MSI was examined by NGS using 7000+ target microsatellite loci. TMB was calculated using only nonsynonymous missense mutations sequenced with a 592-gene panel; a subset of MSI-H tumors also had MMR IHC performed. Analyses examined TMB by MMR protein heterodimer impacted (loss of MLH1/PMS2 vs. MSH2/MSH6 expression) and gene-specific mutations. The sample was 54.6% female; mean age was 63.5 years. Among IHC tested tumors, loss of co-expression of MLH1/PMS2 was more common (n = 544/705, 77.2%) than loss of MSH2/MSH6 (n = 81/705, 11.5%; P < .0001), and was associated with lower mean TMB (MLH1/PMS2: 25.03 mut/Mb vs MSH2/MSH6 46.83 mut/Mb; P < .0001). TMB also varied by tumor histology: colorectal cancers demonstrating MLH1/PMS2 loss had higher TMBs (33.14 mut/Mb) than endometrial cancers (20.60 mut/Mb) and other tumors (25.59 mut/Mb; P < .0001). MMR gene mutations were detected in 42.0% of tumors; among these, MSH6 mutations were most common (25.7%). MSH6 mutation patterns showed variability by tumor histology and TMB. TMB varies by underlying cause(s) of MSI and tumor histology; this heterogeneity may contribute to differences in response to ICI.     

Microsatellite instability and mutation analysis among southern Italian patients with colorectal carcinoma: detection of different alterations accounting for MLH1 and MSH2 inactivation in familial cases.

BACKGROUND: Microsatellite instability (MSI) is due to defective DNA mismatch repair (MMR) and has been detected at various rates in colorectal carcinoma (CRC). The role of MSI in colorectal tumorigenesis was assessed further in this study by both microsatellite analysis of two CRC subsets [unselected patients (n = 215) and patients <50 years of age (n = 95)], and mutation screening of the two major MMR genes MLH1 and MSH2 among familial CRC cases. PATIENTS AND METHODS: PCR-based microsatellite analysis was performed on paraffin-embedded tissues. In CRC families, MLH1/MSH2 mutation analysis and MLH1/MSH2 immunostaining were performed on germline DNA and MSI+ tumour tissues, respectively. RESULTS: The MSI+ phenotype was detected in 75 (24%) patients, with higher incidence in early-onset or proximally located tumours. Among 220 patients investigated for family cancer history, MSI frequency was markedly higher in familial [18/27 (67%)] than in sporadic [32/193 (17%)] cases. Three MLH1 and six MSH2 germline mutations were identified in 14 out of 36 (39%) CRC families. Prevalence of MLH1/MSH2 mutations in CRC families was significantly increased by the presence of: (i) fulfilled Amsterdam criteria; (ii) four or more CRCs; or (iii) one or more endometrial cancer. While MSH2 was found mostly mutated, almost all [8/9 (89%)] familial MSI+ cases with loss of the MLH1 protein were negative for MLH1 germline mutations. CONCLUSIONS: Both genetic (for MSH2) and gene-silencing (for MLH1) alterations seem to be involved in CRC pathogenesis.     

Little evidence for involvement of MLH3 in colorectal cancer predisposition

Mutations in the DNA MMR genes MSH2, MLH1, MSH6 and PMS2 underlie a large subset of HNPCC cases, and a hallmark of the tumors is MSI. In many HNPCC families, however, a causative mutation has not been found. Therefore, the involvement of additional, thus far unknown, genes in MSI as well as MSS colorectal tumor predisposition is possible. The role of a relatively recently cloned MMR gene, MLH3, in familial CRC has been studied; but the results appear somewhat conflicting. To further evaluate the role of MLH3 in CRC predisposition, we analyzed 30 Finnish CRC cases for germline mutations by sequencing. These cases were selected from a large series of Finnish CRC patients, to match features previously proposed to associate with MLH3 germline defects. We found 5 missense variants, 4 of which were also found in Finnish cancer-free controls. The only remaining variant does not appear to be an attractive candidate for a disease-associated mutation because the amino acid change is located outside the conserved residues. We also screened for the previously reported variants, including a frameshift change, the most likely pathogenic MLH3 mutation observed so far. The frameshift was not present in the 30 CRC cases or in 700 cancer-free controls. While it is a difficult task to exclude a role of MLH3 in HNPCC, our study could not confirm a role for MLH3 in CRC predisposition.     

Immunohistochemistry and microsatellite instability testing for selecting MLH1, MSH2 and MSH6 mutation carriers in hereditary non-polyposis colorectal cancer

Hereditary non-polyposis colorectal cancer (HNPCC) represents 1-3% of all colorectal cancers. HNPCC is caused by a constitutional defect in a mismatch repair (MMR) gene, most commonly affecting the genes MLH1, MSH2 and MSH6. The MMR defect results in an increased cancer risk, with the greatest lifetime risk for colorectal cancer and other cancers associated to HNPCC. The HNPCC-associated tumor phenotype is generally characterized by microsatellite instability (MSI) and immunohistochemical loss of expression of the affected MMR protein. The aim of this study was to determine the sensitivity of IHC for MLH1, MSH2 and MSH6, and MSI analysis in tumors from known MMR gene mutation carriers. Fifty-eight paired normal and tumor samples from HNPCC families enrolled in our high-risk colorectal cancer registry were studied for the presence of germline mutations in MLH1, MSH2 and MSH6 by DGGE and direct sequencing. MSI analysis and immunostaining for MLH1, MSH2 and MSH6 were evaluated. Of the 28 patients with a real pathogenic mutation, loss of immunohistochemical expression for at least 1 of these MMR proteins was found, and all except 1 have MSI-H. Sensitivity by MSI analysis was 96%. IHC analysis had a sensitivity of 100% in detecting MMR deficiency in carriers of a pathogenic MMR mutation, and can be used to predict which gene is expected to harbor the mutation for MLH1, MSH2 and MSH6. This study suggests that both analyses are useful for selecting high-risk patients because most MLH1, MSH2 and MSH6 gene carriers will be detected by this 2-step approach. This practical method should have immediate application in the clinical work of patients with inherited colorectal cancer syndromes.