Mutations of the 'minor' mismatch repair gene MSH6 in typical and atypical hereditary nonpolyposis colorectal cancer

Mutations of the mismatch repair (MMR) genes MLH1 and MSH2 are associated with hereditary nonpolyposis colorectal cancer (HNPCC), a highly penetrant autosomal dominant condition characterized by hypermutability of short tandemly repeated sequences in tumor DNA. Mutations of another MMR gene, MSH6, seem to be less common than MLH1 and MSH2 defects, and have been mostly observed in atypical HNPCC families, characterized by a weaker tumor family history, higher age at disease onset, and low degrees of microsatellite instability (MSI), predominantly involving mononucleotide runs. We have investigated the MSH6 gene sequence in the peripheral blood of 4 HNPCC and 20 atypical HNPCC probands. Two frameshift mutations within exon 4 were detected in 2 patients. One mutation was found in a proband from a typical HNPCC family, who had developed a colorectal cancer (CRC), a gastric cancer and a rectal adenoma. The CRC and the adenoma showed mild MSI limited to mononucleotide tracts, while the gastric carcinoma was microsatellite stable. The other mutation was detected in an atypical HNPCC proband, whose CRC showed widespread MSI involving both mono- and dinucleotide repeats. The phenotypic variability associated with MSH6 constitutional mutations represents a complicating factor for the optimization of strategies aimed at identifying candidates to MSH6 genetic testing.     

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...     

Male breast cancer in the hereditary nonpolyposis colorectal cancer syndrome

A male member of a large HNPCC kindred, affected by primary malignancies of the breast and colon, was identified. This individual was found to harbor a germline mutation of the MLH1 mismatch repair gene previously shown to segregate with disease in this kindred. The breast tumor exhibited somatic reduction to homozygosity for the MLH1 mutation, and microsatellite instability was evident in the breast tumor. We conclude that hereditary male breast cancer can occur as an integral tumor in the HNPCC syndrome.     

Association of hereditary hemorrhagic telangiectasia and hereditary nonpolyposis colorectal cancer in the same kindred

Endoglin (CD105) is a proliferation-associated protein that is strongly expressed in endothelial tissue and has a role in tumor angiogenesis. Mutations in endoglin are also linked to Hereditary Hemorrhagic Telangiectasia type 1 (HHT1), an autosomal dominant disease associated with aberrant angiogenesis. We report an unusual association of HHT1 and Hereditary Nonpolyposis Colorectal Cancer (HNPCC) in the same kindred. Genetic analysis indicates that these 2 syndromes are genetically unrelated and separately segregated within the family. The mutation in the endoglin gene leads to a truncated protein. The mutation in the mismatch repair gene MLH1 causes a splicing defect, giving synthesis to an unstable mRNA from this mutated allele. The potential protective role of an endoglin mutation in patients with HNPCC is discussed.     

敲低错配修复基因MSH6抑制结直肠癌细胞上皮间充质转化及其增殖

目的:探究错配修复基因MSH6对结直肠癌细胞的增殖、迁移和侵袭的影响及可能发生的机制。方法:根据美国国家生物信息技术中心(NCBI)中MSH6的基因序列构建靶向敲低MSH6的序列shMSH6-1、shMSH6-2和shMSH6-3,采用细胞转染技术敲低结直肠癌细胞中MSH6的表达,通过实时荧光定量 PCR 检测敲低效率并进行慢病毒包装,应用Western blot在细胞系中筛选MSH6高表达细胞系进行后续实验,应用CCK8检测细胞增殖能力,克隆形成实验检测细胞集落形成能力,伤口愈合和Transwell法检测细胞迁移和侵袭能力,通过Western blot方法检测上皮间充质相关蛋白的表达变化。结果:MSH6在结直肠癌细胞系中表达上调,其中RKO、SW620、LOVO细胞系上调明显,敲低MSH6明显限制了结直肠肿瘤细胞的增殖、迁移和侵袭,同时导致E-cadherin 蛋白水平增加,N-cadherin和Vimentin蛋白表达下降。结论:MSH6在结直肠癌中表达上调,敲低MSH6可抑制结直肠癌细胞的增殖、迁移和侵袭,诱导细胞发生凋亡并能够逆转EMT的发生。     

Validation of predictive models for germline mutations in DNA mismatch repair genes in colorectal cancer

Lynch syndrome is defined by the presence of germline mutations in mismatch repair (MMR) genes. Several models have been recently devised that predict mutation carrier status (Myriad Genetics, Wijnen, Barnetson, PREMM and MMRpro models). Families at moderate‐high risk for harboring a Lynch‐associated mutation, referred to the BC Cancer Agency (BCCA) Hereditary Cancer Program (HCP), underwent mutation analysis, immunohistochemistry and/or microsatellite testing. Seventy‐two tested cases were included. Twenty‐five patients were mutation positive (34.7%) and 47 were mutation negative (65.3%). Nineteen of 43 patients who were both microsatellite stable and normal on immunohistochemistry for MLH1 and MSH2 were also genotyped for mutations in these genes; all 19 were negative for MMR gene mutations. Model‐derived probabilities of harboring a MMR gene mutation in the proband were calculated and compared to observed results. The area under the ROC curves were 0.75 (95%CI; 0.63–0.87), 0.86 (0.7–0.96), 0.89 (0.82–0.97), 0.89 (0.81–0.98) and 0.93 (0.86–0.99) for the Myriad, Barnetson, Wijnen, MMRpro and PREMM models, respectively. The Amsterdam II criteria had a sensitivity and specificity of 0.76 and 0.74, respectively, in this cohort. The PREMM model demonstrated the best performance for predicting carrier status based on the positive likelihood ratios at the >10%, >20% and >30% probability thresholds. In this referred cohort, the PREMM model had the most favorable concordance index and predictive performance for carrier status based on the positive LR. These prediction models (PREMM, MMRPro and Wijnen) may soon replace the Amsterdam II and revised Bethesda criteria as a prescreening tool for Lynch mutations.     

检测微卫星不稳在中国遗传性非息肉病性结直肠癌患者诊断中的应用

背景与目的：遗传性非息肉病性结直肠癌（hereditary nonpolyposis colorectal cancer，HNPCC）是常染色体显性遗传综合征，国外报道90％的HNPCC肿瘤表现为微卫星不稳（microsatellite instability，MSI），可作为筛查HNPCC的金标准。本研究旨在了解中国HNPCC肿瘤MSI发生率以及可疑HNPCC患者大肠癌肿瘤中的MSI发生率，由此探讨大肠癌患者家族中的胃癌等HNPCC相关肿瘤对发现HNPCC患者的意义。方法：选择符合Amsterdam标准的HNPCC组大肠癌标本18例，和不符合Amsterdam标准、但高度怀疑为HNPCC的可疑HNPCC组大肠癌标本16例，检测BAT26、D2S123、BAX、IGFIIR、hMSH3和hMSH66个做卫星位点的微卫星不稳在两组中的发生率，比较两组微卫星不稳频率的差异。结果：上述各傲卫星位点在HNPCC组和可疑HNPCC组标本中均显示较高的突变率。高度微p星不稳肿瘤在两组标本中的检出率分别为94．4％和93．7％．差异无显著性。BAT26对高度微卫星不稳肿瘤敏感度高。结论：MSI在中国HNPCC患者中的发生频率与国外类同。仅用BAT26可发现大部分高度微卫星不稳肿瘤。将胃癌等HNPCC相关肿瘤纳入临床诊断标准，可能有助于避免在中国大肠癌人群中漏诊HNPCC患者。     

Hereditary nonpolyposis colorectal cancer in endometrial cancer patients

Endometrial cancer is the second most common cancer in hereditary nonpolyposis colorectal cancer (HNPCC). It has often been overlooked to explore the possibility of HNPCC in endometrial cancer patients. Our study was to investigate how many HNPCC patients existed among endometrial cancer patients. Among patients who underwent hysterectomy for endometrial cancer at Seoul National University Hospital from 1996 to 2004, 113 patients were included, whose family history and clinical data could be obtained and tumor specimens were available for microsatellite instability (MSI) testing and immunohistochemical (IHC) staining of MLH1, MSH2 and MSH6 proteins. There were 4 (3.5%) clinical HNPCC patients fulfilling the Amsterdam criteria II, and 2 (2/4, 50%) of them carried MSH2 germline mutations. There were also 8 (7.1%) suspected HNPCC (s-HNPCC) patients fulfilling the revised criteria for s-HNPCC, and one (1/8, 12.5%) of them revealed MLH1 germline mutation. In 101 patients, who were not clinical HNPCC or s-HNPCC, 11 patients showed both MSI-high and loss of expression of MLH1, MSH2 or MSH6 proteins, and 2 (2/11, 18.2%) of them showed MSH6 germline mutations. In 113 patients with endometrial cancer, we could find 5 (4.4%) HNPCC patients with MMR germline mutation and 2 (1.8%) clinical HNPCC patients without identified MMR gene mutation. Family history was critical in detecting 3 HNPCC patients with MMR germline mutation, and MSI testing with IHC staining for MLH1, MSH2 and MSH6 proteins was needed in the diagnosis of 2 HNPCC patients who were not clinical HNPCC or s-HNPCC, especially for MSH6 germline mutation.     

遗传性非腺瘤病性结直肠癌的诊治进展

遗传性非腺瘤病性结直肠癌（HNPCC）是一种常染色体显性遗传的综合症,占总的结直肠癌的56%--10%。该病由错配修复基因缺陷造成,肿瘤表现出高度的微卫星不稳。临床上辨别HNPCC患者对诊断和治疗以及监测HNPCC家庭成员发病有指导意义。     

Prevalence of germline mutations of MLH1 and MSH2 in hereditary nonpolyposis colorectal cancer families from Spain

HNPCC is an autosomal dominantly inherited cancer-susceptibility syndrome that confers an increased risk for colorectal cancer and endometrial cancer at a young age. It also entails an increased risk of a variety of other tumors, such as ovarian, gastric, uroepithelial and biliary tract cancers. The underlying pathogenic mutation lies in 1 of the 5 known DNA MMR genes (MSH2, MLH1, PMS1, PMS2 and MSH6). We screened a total of 140 individuals from 56 Spanish families with suspected HNPCC for mutations in the DNA mismatch repair genes MLH1 and MSH2, using DGGE and direct DNA sequencing. Families were selected on the basis of a history of HNPCC-related tumors or the occurrence of other associated tumors in members besides the index case affected with colorectal cancer. We detected 14 definite pathogenic germline mutations, 9 in MLH1 and 5 in MSH2 in 13 unrelated families selected by the Amsterdam criteria and Bethesda guidelines (1 family carries 2 mutations) and 3 missense mutations in 3 unrelated families selected by the Amsterdam criteria. Among the 17 germline mutations noted in the Spanish cohort, 10 are novel, 7 in MLH1 and 3 in MSH2, perhaps demonstrating different mutational spectra in the Spanish population, where no founder mutation has been identified. Based on our results, we suggest that in the Spanish population not only HNPCC families fulfilling the Amsterdam criteria but also those following Bethesda guidelines should undergo genetic testing for MSH2 and MLH1 mutations.     

Mismatch repair polymorphisms and the risk of colorectal cancer

Rare germline variants in mismatch repair genes have been linked to hereditary nonpolyposis colorectal cancer; however, it is unknown whether common polymorphisms in these genes alter the risk of colorectal cancer. To examine the association between common variants in mismatch repair genes and colorectal cancer, we conducted a case-cohort study within the CLUE II cohort. Four single nucleotide polymorphisms in 3 mismatch repair genes (MSH3 R940Q, MSH3 T1036A, MSH6 G39E and MLH1 I219V) were genotyped in 237 colorectal cancer cases and a subcohort of 2,189 participants. Incidence rate ratios (RRs) and 95% confidence intervals (95% CIs) for each polymorphism were estimated. The MSH3 1036A variant was found to be associated with an increased risk of colorectal cancer (RR=1.28, 95% CI: 0.94-1.74 and RR=1.65, 95% CI: 1.01-2.70 for the AT and TT genotypes, respectively, with p(trend)=0.02), particularly proximal colon cancer. Although the MSH3 940Q variant was only weakly associated with colorectal cancer overall (p(trend)=0.07), it was associated with a significant increased risk of proximal colon cancer (RR=1.69, 95% CI: 1.10-2.61 and RR=2.68, 95% CI: 0.96-7.47 for the RQ and QQ genotypes, respectively with p(trend)=0.005). Processed meat intake appeared to modify the association between the MSH3 polymorphisms and colorectal cancer (p(interaction) < 0.10 for both). No association was observed with the MSH6 and MLH1 polymorphisms overall. This study suggests that common polymorphisms in the mismatch repair gene, MSH3, may increase the risk of colorectal cancer, especially proximal colon cancer.     

Surveillance for endometrial cancer in hereditary nonpolyposis colorectal cancer syndrome

The estimated lifetime risk for endometrial carcinoma (EC) in hereditary nonpolyposis colorectal cancer syndrome (HNPCC) is 32-60%, thus supporting surveillance. The survival rate of EC patients is, however, favourable questioning the need for surveillance. Yet, the effectiveness of gynecological surveillance remains to be shown. The 2 previously published studies were based on transvaginal ultrasound (TVUS) alone. Intrauterine biopsy has not been tested in surveillance for EC in HNPCC families. The effect of gynecological surveillance was evaluated among 175 Finnish mutation carriers. During 759 person years at risk, there were 503 surveillance visits including TVUS and intrauterine biopsy of endometrium at 94% and 74% of the visits, respectively. EC occurred in 14 cases, 11 of which were diagnosed by surveillance, 8 by intrauterine biopsies. TVUS indicated only 4 EC patients but missed 6 other cases. Intrauterine sampling detected 14 additional cases of potentially premalignant hyperplasia. The stage distribution and survival tended to be more favorable in the 14 EC cases of the surveilled group (no deaths) than in the group of 83 symptomatic mutation carriers of whom 6 died of EC, but with no statistical significance. Four cases of ovarian cancer occurred but none was detected by surveillance in TVUS examinations. In conclusion, EC surveillance in HNPCC seems more effective with endometrial biopsies than with TVUS alone. A definite improvement in survival remains to be shown. The detection of early cancer stages and premalignant lesions offers the opportunity to avoid extensive adjuvant treatment.     

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.     

错配修复基因hMLH3在家族性食管癌中的意义

目的：探讨错配修复基因hMLH3在家族性食管癌发生与发展中的作用。方法：应用聚合酶链反应（PCR）、变性高效液相色谱分析（DHPLC）和直接测序法对10个有遗传背景的食管癌家族（66名成员）,检测hMLH3基因所有外显子（共12个）的突变。对发现的基因改变,在家系内进行分离分析,并与在96例散发性食管癌患者和96例正常对照中发生的频率相比较。结果：在4个家系中共发现了4个错义突变和3个碱基多态性,而4个错义突变在各自家系中的发生频率均高于散发性食管癌患者和正常对照中的频率。在家系9（A2173C）和10（C2825T）中,hMLH3的突变可能具有致病性,但外显率下降;而在家系1（T3826C）和7（T3826C）的结果不支持它是单一的高风险基因。结论：hM-LH3基因在某些家族性食管癌中可能为高风险基因,但外显率下降,而在某些家系中可能仅为一低风险的基因,它诱导肿瘤的产生可能通过与其他基因相互叠加、共同起作用。     

Deficient mismatch repair system in patients with sporadic advanced colorectal cancer

A deficient mismatch repair system (dMMR) is present in 10–20% of patients with sporadic colorectal cancer (CRC) and is associated with a favourable prognosis in early stage disease. Data on patients with advanced disease are scarce. Our aim was to investigate the incidence and outcome of sporadic dMMR in advanced CRC. Data were collected from a phase III study in 820 advanced CRC patients. Expression of mismatch repair proteins was examined by immunohistochemistry. In addition microsatellite instability analysis was performed and the methylation status of the MLH1 promoter was assessed. We then correlated MMR status to clinical outcome. Deficient mismatch repair was found in only 18 (3.5%) out of 515 evaluable patients, of which 13 were caused by hypermethylation of the MLH1 promoter. The median overall survival in proficient MMR (pMMR), dMMR caused by hypermethylation of the MLH1 promoter and total dMMR was 17.9 months (95% confidence interval 16.2–18.8), 7.4 months (95% CI 3.7–16.9) and 10.2 months (95% CI 5.9–19.8), respectively. The disease control rate in pMMR and dMMR patients was 83% (95% CI 79–86%) and 56% (30–80%), respectively. We conclude that dMMR is rare in patients with sporadic advanced CRC. This supports the hypothesis that dMMR tumours have a reduced metastatic potential, as is observed in dMMR patients with early stage disease. The low incidence of dMMR does not allow drawing meaningful conclusions about the outcome of treatment in these patients.     

遗传性非息肉病性结直肠癌7个家系的临床分析

目的:总结遗传性非息肉病性结直肠癌(HNPCC)家系的临床特点,提高临床诊断和治疗水平。方法:收集7个HNPCC家系的病例资料,分析其发病特点并记录随访结果。结果:7个HNPCC家系共有癌症患者23例,肿瘤灶27处:大肠外瘤灶3处;大肠瘤灶24处,其中有13处位于脾曲近侧结肠,占54.1%。平均发病年龄为41.2岁,17例(73.5%)发病在50岁以前。1家系累及连续三代人、4家系累及连续两代人。多原发癌患者4例,其中3例为肠外癌。结论:HNPCC具有发病年龄轻、垂直传递、肠外癌发病率高、常见多原发癌、好发于右半结肠、病理分化较差的特点,但预后相对较好。     

Familial colorectal adenocarcinoma and hereditary nonpolyposis colorectal cancer: a nationwide epidemiological study from Sweden

Although estimates are available of the proportion of hereditary nonpolyposis colorectal cancer (HNPCC) among all colorectal cancer (CRC), its proportion among familial CRC is unclear. We estimated these proportions epidemiologically from the nationwide Swedish Family-Cancer Database on 9.6 million individuals. Colorectal adenocarcinomas were retrieved from the Cancer Registry covering years 1958-1996. Standardized incidence ratios (SIRs) were calculated for offspring (aged less than 62 years) when their parent had colorectal adenocarcinoma. In 9.82% of all families, an offspring and a parent were affected, giving a population attributable proportion of 4.91% and a familial SIR of 2.00. When offspring and parents shared the anatomic site, the SIR was 2.32 for proximal and 2.00 for distal CRC. When offspring were diagnosed before age 40 years and parents before age 50 years, the SIR was 25.72 for familial proximal CRC. In older age groups familial risks did not differ between proximal and distal CRC. Familial risks were increased also for endometrial, small intestinal and gastric cancers, manifestations in HNPCC. Depending on which assumptions were made, HNPCC was calculated to account for 20 to 50% of familial CRC, corresponding to 1 or 2.5% of all CRC among 0-61-year-old individuals.     

DNA mismatch repair gene polymorphisms affect survival in pancreatic cancer

Purpose.

DNA mismatch repair (MMR) maintains genomic stability and mediates cellular response to DNA damage. We aim to demonstrate whether MMR genetic variants affect overall survival (OS) in pancreatic cancer.

Materials and Methods.

Using the Sequenom method in genomic DNA, we retrospectively genotyped 102 single-nucleotide polymorphisms (SNPs) of 13 MMR genes from 706 patients with pancreatic adenocarcinoma seen at The University of Texas MD Anderson Cancer Center. Association between genotype and OS was evaluated using multivariable Cox proportional hazard regression models.

Results.

At a false discovery rate of 1% (p ≤ .0015), 15 SNPs of EXO1, MLH1, MSH2, MSH3, MSH6, PMS2, PMS2L3, TP73, and TREX1 in patients with localized disease (n = 333) and 6 SNPs of MSH3, MSH6, and TP73 in patients with locally advanced or metastatic disease (n = 373) were significantly associated with OS. In multivariable Cox proportional hazard regression models, SNPs of EXO1, MSH2, MSH3, PMS2L3, and TP73 in patients with localized disease, MSH2, MSH3, MSH6, and TP73 in patients with locally advanced or metastatic disease, and EXO1, MGMT, MSH2, MSH3, MSH6, PMS2L3, and TP73 in all patients remained significant predictors for OS (p ≤ .0015) after adjusting for all clinical predictors and all SNPs with p ≤ .0015 in single-locus analysis. Sixteen haplotypes of EXO1, MLH1, MSH2, MSH3, MSH6, PMS2, PMS2L3, RECQL, TP73, and TREX1 significantly correlated with OS in all patients (p ≤ .001).

Conclusion.

MMR gene variants may have potential value as prognostic markers for OS in pancreatic cancer patients.     

Mismatch repair gene defects in sporadic colorectal cancer enhance immune surveillance

Background

There is evidence that colorectal cancers (CRC) with DNA mismatch repair deficiency (MMR-D) are associated with a better prognosis than the generality of large bowel malignancies. Since an active immune surveillance process has been demonstrated to influence CRC outcome, we investigated whether MMR-D can enhance the immune response in CRC.

Patients and Methods

A group of 113 consecutive patients operated for CRC (42 stage I or II and 71 with stage III or IV) was retrospectively analyzed. The expression of MMR genes (MSH2, MLH1, MSH6 and PSM2) and co-stimulatory molecule CD80 was assessed by tissue microarray immunohistochemistry. In addition, tumor infiltrating mononuclear cells (TIMC) and T cell subpopulations (CD4, CD8, T-bet and FoxP-3) were quantified. The effect of specific siRNA (siMSH2, siMLH1, siMSH6 and siPSM2) transfection in HT29 on CD80 expression was quantified by flow cytometry. Non parametric statistics and survival analysis were used.

Results

Patients with MMR-D showed a higher T-bet/CD4 ratio (p = 0.02), a higher rate of CD80 expression and CD8 lymphocyte infiltration compared to those with no MMR-D. Moreover, in the MMR-D group, the Treg marker FoxP-3 was not expressed (p = 0.05). MMR-D patients with stage I or II and T-bet expression had a significant better survival (p = 0.009). Silencing of MSH2, MLH1 and MSH6, but not PSM2, significantly increased the rate of CD80+ HT29 cells (p = 0.007, p = 0.023 and p = 0.015, respectively).

Conclusions

CRC with MMR-D showed a higher CD80 expression, and CD8+ and Th1 T-cell infiltration. In vitro silencing of MSH2, MLH1 and MSH6 significantly increased CD80+ cell rate. These results suggest an enhanced immune surveillance mechanism in presence of MMR-D.