Microsatellite Instability In Colorectal Carcinoma Research Articles

Significance of Microsatellite Instability in Colorectal Carcinoma- A Complete Review

The microsatellite instability (MSI-H) or mismatch repair deficient (dMMR) colorectal tumors recently have been reported that can benefit from immunotherapy, and MSI can be used as a genetic instability of a tumor detection index. Many studies have shown that there are many heterogeneous phenomena in patients with MSI tumors in terms of immunotherapy, prognosis and chemotherapy sensitivity. Here we mainly review the research results of MSI detection methods, its mechanisms, occurrence and its relationship with related tumors, aiming in such a way for brief analysis of the micro satellite instability. Microsatellites (MS) are the repeated sequences of DNA that play an important role in maintaining the tissue morphology. Any mutation of the DNA or chromosomes, lead to the instability of the microsatellites, thereby causing the microsatellite instability. There are three types of microsatellite instability (MSI). High microsatellite instability (MSI-H), low microsatellite instability (MSI-L) and microsatellite stability (MSS). Recent clinical research tends to classify MSS-L and MSS as similar. Microstaellite instability plays an important role in colorectal carcinoma. Based on different molecular mechanisms, MSI in colorectal cancer can be divided into colorectal cancer (CRC) with no obvious family genetic history and Lynch syndrome with non-polyposis with family genetic history. Lynch syndrome is an autosomal dominant disorder and syndrome caused by mutations in MMR strains, and it can also cause tumors in other parts of the colon and rectum. With the recent development of MSI detection technology and immunosuppressant in tumor therapy, researchers found that MSI-H tumors respond well to immunotherapy. There are several methods to detect the microsatellite instability. 1. Next Generation sequencing (NGS), 2. Fluoresence multiplex PCR and capillary electrophoresis. 3. Immunohistochemistry. 4. Single molecule- molecular inversion probes (SmMIP). The main mechanism of MSI includes, Slipped strand mispairing, MMR deficient.

English

BACKGROUND Colorectal cancer (CRC) is one of the leading causes of mortality and morbidity from cancer. The risk group ranges from 69-79 years and the mean age being 62 years. This study was done to assess and compare the clinicopathological characteristics of colorectal carcinoma in adults above and below 50 years and also study the expression of MLH1 for demonstration of microsatellite instability in colorectal carcinoma. METHODS This was a cross-sectional study conducted in the Government Medical College, Trivandrum, Kerala, after obtaining ethical committee clearance (IEC.15/18/2017/MCT dt 19/12/2017). All cases of colorectal carcinomas that had surgical resection and the specimen brought to the Pathology department were included in the study. Carcinomas which were secondary deposits from elsewhere were excluded. Sample size was 61 calculated using the formula n=4pq/d2. Study variables included age, site, histology type, stage, differentiation, lymphatic and vascular spread and lymphocyte infiltration were recorded. Routine H&E sections were used to observe the morphology, invasion, grade, and stage of the tumours. Then MSI was detected using MLH I. Clinical details were collected from the patients and medical records. Data were entered in excel sheets. categorical variables are expressed as proportions and quantitative variables are expressed as mean and standard deviation. Chi square test was used as the test of significance for categorical variables. RESULTS Clinicopathological features of 61 cases were studied and the mean age was 61 years. Most cases were left-sided cancer with moderately differentiated classical adenocarcinoma being the most common histopathological subtype. Individuals less than 50 years presented with adenocarcinoma with mucinous and signet ring cell morphology and with poor differentiation. 67.2 % had no lymphovascular invasion. The majority of the cases were positive for MLH1. The cases which showed negativity for MLH1 were cases with mucinous differentiation or signet ring cell type and were predominantly moderate to poorly differentiated and this relation was found to be significant. CONCLUSIONS The study concludes that the majority of CRC occurred in individuals between 61 - 70 years of age, they were left-sided moderately differentiated adenocarcinomas with stage IIB disease, most were negative for lymphovascular invasion and tumour infiltrating lymphocytes. Younger patients had a higher percentage of mucinous and signet-ring cell histology. 78.7 % were positive for MLH1. KEY WORDS Colorectal carcinoma, MLH1, Microsatellite instability

Targeted next-generation sequencing-based detection of microsatellite instability in colorectal carcinomas.

In the present study, we developed a computational method and panel markers to assess microsatellite instability (MSI) using a targeted next-generation sequencing (NGS) platform and compared the performance of our computational method, mSILICO, with that of mSINGS to detect MSI in CRCs. We evaluated 13 CRC cell lines, 84 fresh and 119 formalin-fixed CRC tissues (including 61 MSI-high CRCs and 155 microsatellite-stable CRCs) and tested the classification performance of the two methods on 23, 230, and 3,154 microsatellite markers. For the fresh tissue and cell line samples, mSILICO showed a sensitivity of 100% and a specificity of 100%, regardless of the number of panel markers, whereas for the formalin-fixed tissue samples, mSILICO exhibited a sensitivity of up to 100% and a specificity of up to 100% with three differently sized panels ranging from 23 to 3154. These results were similar to those of mSINGS. With the application of mSILICO, the small panel of 23 markers had a sensitivity of ≥95% and a specificity of 100% in cell lines/fresh tissues and formalin-fixed tissues of CRC. In conclusion, we developed a new computational method and microsatellite marker panels for the determination of MSI that does not require paired normal tissues. A small panel could be integrated into the targeted NGS panel for the concurrent analysis of single nucleotide variations and MSI.

Diagnostic test assessment. Validation study of an alternative system to detect microsatellite instability in colorectal carcinoma.

SummaryThe American Society for Clinical Pathology (ASCP), College of American Pathologists (CAP), Association for Molecular Pathology (AMP), and the American Society of Clinical Oncology (ASCO) have been recently strongly recommended the evaluation of mismatch repair status (MMS) as molecular biomarkers in colorectal cancer for a better prognostic stratification of patients. This recommendation is emphasized by the recent evidence of Microsatellite Instability (MSI) as a predictive marker for chemotherapy and immunotherapy.In this scenario, the validation of molecular biomarker testing methods seems to be essential to design the most appropriate tailored therapy and the most suitable care strategy, respectively.In this study, we validated an alternative method based on capillary electrophoresis system label-free PCR (Qiaxcel system) to evaluate the MSI Bethesda Panel. We also parallel the results with a standard approach.Our data showed total concordance with the standard approach, with a highly time-efficient and easy procedure combined with high sensitivity for MSI detection.Alternative capillary electrophoresis based on label-free PCR such as the Qiaxel system is a very sensitive and specific method to detect MSI for the management of patients with colorectal cancer. This procedure is adequate and suitable in diagnostic routine for the evaluation of microsatellite repeats compared to standard procedures.

Mismatch Repair Proteins and Microsatellite Instability in Colorectal Carcinoma (MLH1, MSH2, MSH6 and PMS2): Histopathological and Immunohistochemical Study

BACKGROUND:Colorectal cancer (CRC) is one of the most common cancers worldwide. Microsatellite instability (MSI) is detected in about 15% of all colorectal cancers. CRC with MSI has particular characteristics such as improved survival rates and better prognosis. They also have a distinct sensitivity to the action of chemotherapy.AIM:The aim of the study was to detect microsatellite instability in a cohort of colorectal cancer Egyptian patients using the immunohistochemical expression of mismatch repair proteins (MLH1, MSH2, MSH6 and PMS2).MATERIAL AND METHODS:Cases were divided into Microsatellite stable (MSS), Microsatellite unstable low (MSI-L) and Microsatellite unstable high (MSI-H). This Microsatellite stability status was correlated with different clinicopathological parameters.RESULTS:There was a statistically significant correlation between the age of cases, tumor site & grade and the microsatellite stability status. There was no statistically significant correlation between the gender of patients, tumor subtype, stage, mucoid change, necrosis, tumor borders, lymphocytic response, lymphovascular emboli and the microsatellite stability status.CONCLUSION:Testing for MSI should be done for all colorectal cancer patients, especially those younger than 50 years old, right sided and high-grade CRCs.

Significance of Dna Mismatch Repair Genes and Microsatellite Instability in Colorectal Carcinoma in Ibadan, Nigeria

Background: Though the incidence of colorectal carcinoma (CRC) is relatively uncommon in Nigeria, compared to the developed countries, recent studies indicate an increasing trend. Our patients often present at an earlier age, which has important implications for the pathogenesis in Nigeria. MLH1, MSH2, MSH6, PMS2 are the commonly mutated MMR genes in descending order of frequency, with PMS1 and MLH3 mutations being very rare. This study attempts to determine the significance of microsatellite instability (MSI) in colorectal carcinogenesis using immunohistochemistry (IHC) for detection of defects of DNA mismatch repair gene (MMR) amongst cases diagnosed at University College Hospital (UCH) Ibadan, Nigeria. Methodology: Suitable consecutive CRC cases identified from UCH, Ibadan, Pathology Department, 2006 files were stained with MMR IHC antibody panel (MLH1, MSH2, MSH6, PMS2). Stained sections were reviewed for nuclear reactivity and graded according to staining intensity (weak +, moderate ++, strong +++, very strong ++++). Result: IHC was performed on 26 cases. The age range is 22-74 years with 9 cases <40 years. One case with no reactivity with any of the antibody was considered unsuitable. Two cases with only PMS2 nuclear reactivity but no reaction with other antibodies were considered equivocal. Five cases had no nuclear reactivity with single antibody: MLH1 (2); MSH2 (3); and one case had no nuclear reactivity with MLH1 & MSH2. These six cases included 3 cases aged 22, 27 and 32 years with tumors showing no nuclear reactivity for MSH2 and (MLH1 & MSH2) respectively. Conclusion: Though the number cases tested are small, the identification of the loss of MMR gene protein (MLH1 and MSH2) by IHC, indicating MSI, in a significant number of the 26 cases tested (23%), particularly young individuals, suggests that defects of DNA mismatch repair genes are important factors in colorectal carcinogenesis in Nigerians.

The analysis of microsatellite instability in extracolonic gastrointestinal malignancy

Microsatellite instability (MSI) is a genetic feature of sporadic and familial cancers of multiple sites and is related to defective mismatch repair (MMR) protein function. Lynch syndrome (LS) is a familial form of MMR deficiency that may present with a spectrum of MSI positive cancers including gastrointestinal (GI) malignancies. The incidence of high level MSI (MSI-H) in colorectal carcinoma is well defined in both familial and sporadic cases and these tumours portend a better overall prognosis in colorectal carcinoma (CRC). There are certain morphological features that suggest MSI-H CRC and international guidelines have been established for the evaluation of MSI in CRC. The prevalence and morphological features of extracolonic GI MSI-H tumours are less well documented. Furthermore, it is unclear whether the guidelines for the assessment of MSI in CRC are appropriate for application to extracolonic GI malignancies. This review aims to summarise the recent literature on MSI in extracolonic LS-related GI tract malignancies with special attention to the assessment of the MMR system by evaluation of specific microsatellite markers and/or immunohistochemical evaluation of MMR protein expression. The reported prevalence of sporadic and LS-related MSI-H tumours along with their associated unique morphological patterns and related prognostic or therapeutic implications will be discussed.

CD133 mRNA expression and microsatellite instability in colorectal carcinoma

The present study was performed to examine the CD133 expression in colorectal cancer and to analyze its relationship with microsatellite instability (MSI) and the clinicopathological factors, including patient survival. The CD133 mRNA levels in 61 primary colorectal adenocarcinomas were analyzed by reverse transcriptase-polymerase chain reaction, with normalization relative to GAPDH. Five microsatellite markers were analyzed to evaluate MSI. A CD133 mRNA expression was significantly associated with the depth of invasion (P = 0.017), lymph node involvement (P = 0.012), and lymphovascular invasion (P = 0.019). A CD133 expression was significantly correlated with the MSI status (P = 0.035). With a median follow-up period of 45 months, the 5-year disease-free survival rate of patients with a low CD133 mRNA expression was significantly higher than that of those patients with high levels of CD133 mRNA expression (82.9% and 59.0%, respectively; P = 0.027). However, on the multivariate analysis, a CD133 mRNA expression was not an independent predictor of disease-free survival. Elevated CD133 mRNA levels may represent more aggressive tumor biology and poorer survival in patients with colorectal cancer, correlating with a high level of MSI status. Larger prospective studies are required to confirm these findings.

19. Correlation between loss of mismatch repair enzyme expression and microsatellite instability in colorectal carcinomas in a general hospital setting

Aims To audit the correlation between immunostaining for DNA mismatch repair enzymes performed in routine diagnostic practice and the results of microsatellite instability analysis in colorectal carcinomas. Methods Immunostains for MLH1, MSH2, MSH6 and PMS2 were performed as part of the regular histopathological investigation of carcinomas of the large intestine. The microsatellite instability status was determined for all cases reported as showing loss of immunoexpression or equivocal immunoexpression. Results The study population consisted of 153 patients, of which 28 (18%) were classified as showing loss of immunoexpression, and 29 (19%) were classified as equivocal. All of the cases classified as showing loss of expression were microsatellite unstable. Of the 29 cases with equivocal expression, only one case was unstable on microsatellite analysis. Conclusions Loss of immunoexpression for mismatch repair enzymes can be reported reliably in a general hospital setting, and had a positive predictive value in this series of 100%. In our experience, an equivocal report on immunostaining was generally found in stable carcinomas. Microsatellite instability (MSI) is found in about 15% of colorectal carcinomas. In most cases, it is a sporadic phenomenon due to loss of expression of the enzyme MLH1 as a result of hypermethylation of the promoter region. Occasionally, it is due to a germline mutation in a gene encoding one of the DNA mismatch repair enzymes; such patients have Lynch syndrome, or hereditary non-polyposis colorectal cancer. Whether sporadic or hereditary, cancers with loss of DNA mismatch repair function exhibit a high level of instability in microsatellite regions of DNA and are described as unstable or showing high levels of MSI (MSI-H). To audit the correlation between immunostaining for DNA mismatch repair enzymes performed in routine diagnostic practice and the results of microsatellite instability analysis in colorectal carcinomas. Immunostains for MLH1, MSH2, MSH6 and PMS2 were performed as part of the regular histopathological investigation of carcinomas of the large intestine. The microsatellite instability status was determined for all cases reported as showing loss of immunoexpression or equivocal immunoexpression. The study population consisted of 153 patients, of which 28 (18%) were classified as showing loss of immunoexpression, and 29 (19%) were classified as equivocal. All of the cases classified as showing loss of expression were microsatellite unstable. Of the 29 cases with equivocal expression, only one case was unstable on microsatellite analysis. Loss of immunoexpression for mismatch repair enzymes can be reported reliably in a general hospital setting, and had a positive predictive value in this series of 100%. In our experience, an equivocal report on immunostaining was generally found in stable carcinomas.

Sporadic Colon Cancer: Mismatch Repair Immunohistochemistry and Microsatellite Instability in Omani Subjects

Colorectal carcinoma (CRC) is the most common gastrointestinal malignancy in the world, and there are suggestions of a particularly high incidence in the Middle East, including those of African origin. Defects in DNA mismatch repair (MMR) systems are involved in the carcinogenesis of both sporadic and inherited human cancers. We assessed colonic cancers in an attempt to identify tumors with DNA MMR deficiency and microsatellite instability (MSI). Additionally, we tested the ability of cell cycle regulator p16 that effects cell proliferation and can be abrogated by hypermethylation of the promoter region. We reviewed the charts of 756 patients who were referred to the Oman major colonoscopy unit of the Sultan Qaboos University Hospital and Royal Hospital from the years 2000 to 2004. Colon cancer tissue was assayed using immunohistochemistry for expression of hMLH1 and hMSH2, and a panel of five pairs of microsatellite primers (NR21, NR22, NR24, BAT25, and BAT26) for MSI-H analysis and additional dinucleotide markers (D17S250, D5S346, and D2S123) used for MSI-L. The expression status of MMR genes and MSI was correlated with cancer stage, location, and histology. A total of 49 tumors were analyzed for histopathology, MSI, and hMLH1/hMSH2 protein expression analysis. The methylation status of the p16 promoter was determined by methylation-specific polymerase chain reaction (PCR). The mean age for the carcinomas was 52.2 years and 53% of the patients were male. The majority of the tumors were left-sided. The information currently available indicates that there is an incidence of 4.7% colon cancer (49/1036) and 12.1% (126/1290) colon adenoma among the cases who underwent colonoscopy at these centers. The rate of MSI-H was 12.2% (n = 6), which appears to be the same as previously reported in literature. Eight of 49 tumors (16.3%) were MMR defective by IHC. Defects in the mismatch repair genes hMLH1 and hMSH2 were found in four (66.7%) and two (33.3%) of CRCs MSI-H cases, respectively. Defects in hMLH1 expression in tumors were commonly associated with moderate differentiation. The p16 promoter was methylated in 4% of tumors. This is the first genetic study of CRC in this region of the world to demonstrate the incidence of MSI, p16 methylation, and hMLH1 and MSH2 expression in the Omani population. In addition, a relatively high frequency of CRC in younger age groups was noted, which is an important observation. The left-sided preponderance of MMR defective tumors was mostly associated with hMLH1, and with possible loss of hMSH2 expression, an observation that differs from studies on other populations. In conclusion, although the overall rate of CRC is unknown in this region, the frequency of MSI in CRC in this region appears to be the same as in Caucasians in the USA.

The features of host immune response with respect to microsatellite status of colorectal cancer

Background: The genetic alterations in colorectal cancer (CRC) progression are determined by two separate pathways, chromosomal and microsatellite instability (MSI). The CRCs with MSI have distinct clinicopathological characteristics with pronounced tumor-associated immune responses. The aim of our study was to investigate the intensity of host immune response in CRC tissue by comparing microsatellite stable (MSS) and instable tumors. Methods: The study was performed on CRC specimens from 28 patients with MSI and compared with 30 MSS tumors. The microsatellite status was evaluated with two markers by PCR and melting point analysis. The immunostaining with anti-CD3 pan-T cell antibody was used to quantify the number of tumor infiltrating lymphocytes. The lymphocytes in peritumoral stromal and the Crohn?s-like peritumoral reaction were counted on H&amp;E slides. Results: No significant differences were found in the average number of lymphocytes in peritumoral stroma and in clinicopathological characteristics of CRCs. The conspicuous Crohn?s-like lymphoid reactions were present in 67.86% of CRCs with MSI versus 26.66% of MSS cases. The CRCs with MSI cases carried significantly higher numbers of tumor infiltrating T-lymphocytes (13.21 versus 7.47) (p&lt;0.0001). Conclusion: The presences of peritumoral Crohn?s-like lymphoid and intraepithelial lymphocytic reaction were intensive markers for MSI in colorectal carcinomas in our study. The peculiar genetic instability in MSI tumors may lead to a continuous production of abnormal peptides, which act as neoantigens. They could induce specific antitumor immune responses effective in limiting tumor growth and spread. Abnormal peptides are potentially promising in immunotherapy advancing and in the design of a vaccine against colorectal tumors with MSI.

Assessment of microsatellite instability in colorectal carcinoma at an Indian center

The purpose of the present study was to evaluate the frequency of microsatellite instability (MSI) in colorectal cancers in an Indian cohort. Paraffin embedded tissue samples of colorectal cancers from 46 patients were assessed for mismatch repair protein expression (hMLH1 and hMSH2) by immunohistochemistry. Subsequently, MSI analysis was done after PCR amplification of five Bethesda markers. Amongst 46 cases studied, only 5 patients (10.8%) showed MSI. Out of these, two (4.3%) had high microsatellite instability (MSI-H) and three (6.5%) showed low microsatellite instability (MSI-L). Out of 46 cases, 41 were microsatellite stable (MSS). In the 46 cases tested by immunohistochemistry, 7 (15.7%) showed the absence of hMLH1 and 1 case showed the absence of hMSH2. Our study indicates a similar rate of incidence of MSI in colorectal cancers in the Indian cohort compared to the West (10-15%) despite lower incidence of colorectal cancers and predominance of rectosigmoid tumors in the Indian population.

Age‐related alteration in the association of microsatellite instability with absent hMLH1 expression and histological types of colorectal carcinoma

Microsatellite instability (MSI) is present in approximately 15-20% of sporadic colorectal cancers. However, despite the increased prevalence of absent hMLH1 expression and MSI in colorectal cancer in the elderly, few attempts have been made to define it in detail. The aim of the present paper was to correlate age-related alterations in absent hMLH1 expression and MSI with various histological types of colorectal carcinoma. hMLH1 expression and microsatellite status were studied in 184 colorectal carcinomas (49 well-differentiated, 49 moderately differentiated, 49 poorly differentiated adenocarcinomas, and 37 mucinous carcinomas). The prevalence of absent hMLH1 expression was higher in poorly differentiated adenocarcinoma (63%) and mucinous carcinoma (43%) than in well- (8%) and moderately (12%) differentiated adenocarcinomas. MSI was found more frequently in poorly differentiated adenocarcinoma (69%) and mucinous carcinoma (41%) than in well- and moderately differentiated adenocarcinomas (8% and 6%, respectively). Age-related differences in absent hMLH1 expression and MSI were found only in poorly differentiated adenocarcinoma, in which the prevalence of medullary-type carcinoma increased with advancing age. These results indicate that an age-related increase of medullary-type tumors in poorly differentiated adenocarcinoma may play an important role in the increase of absent hMLH1 expression and MSI in colorectal carcinoma.

A Novel Logistic Model Based on Clinicopathological Features Predicts Microsatellite Instability in Colorectal Carcinomas

High-frequency microsatellite instability has been reported to be associated with good prognosis in colorectal adenocarcinoma. However, methods to assess microsatellite instability (MIN) are based on genetic assays and are not ideally suited to most histopathology laboratories. The aim of the present study was to develop a model for prediction of MIN status in colorectal cancer based on phenotypic characteristics. Clinicopathological features of a cohort of 204 patients with primary colon cancer were retrospectively reviewed following predetermined criteria. Genetic assessment of MIN status was performed on DNA extracted from sections of formalin-fixed, paraffin-embedded specimens by testing a panel of 11 microsatellite markers. Logistic regression analysis generated a mathematical tool capable of identifying colorectal tumors displaying MIN status with a sensitivity of 77.8% and a specificity of 96.8%. Features associated with instability included the proximal location of the lesions, occurrence of solid and/or mucinous differentiation, absence of cribriform structures, presence of peritumoral Crohn-like reaction, expansive growth pattern, high Ki67 proliferative index, and p53-negative phenotype. This approach predicts microsatellite instability in colorectal carcinoma with an overall assigned accuracy of 95.1% and a negative predictive value of 97.8%. Implementation of this tool to routine histopathological studies could improve the management of patients with colorectal cancer, especially those presenting with stage II and III of the disease. It will also assist in identifying a subset of patients likely to benefit from adjuvant chemotherapy.

Mitochondrial microsatellite instability in colorectal carcinomas—frequency and association with nuclear microsatellite instability

The D310 mononucleotide repeat in the D-loop region in mitochondrial DNA has been identified as a hotspot for alterations in primary tumours. We examined D310 alterations as well as repeats in the ND1 and ND5 genes, in 95 colorectal carcinomas and in 95 controls without known gastrointestinal malignancy. D310 alterations were found in 32 (34%) of the carcinomas, in contrast to two persons (2%) in the control group. Thus, when frequency is concerned, D310 seems to be a hotspot for alterations in colorectal cancer. No mutations were found in the ND1 and ND5 genes. D310 instability was not associated with nuclear microsatellite instability, indicating different mechanisms of occurrence.

Different gene expression profiles between microsatellite instability-high and microsatellite stable colorectal carcinomas.

Recent molecular genetic studies have revealed that two major types of genomic instabilities, chromosomal instability (CIN) and microsatellite instability (MSI), exist in colorectal carcinomas. In order to clarify the molecular signature related to the CIN and MSI in colorectal carcinomas, we performed transcriptomic expression analysis on eight microsatellite instability-high (MSI-H) colorectal carcinomas and compared the results obtained with that of nine microsatellite stable (MSS) colorectal carcinomas using oligonucleotide microarrays containing 17 334 known genes and 1331 unknown genes or expression sequence tags (ESTs). Unsupervised two-way hierarchical clustering with 5724 genes successfully classified tumors from normal mucosa, and displayed a distinctive MSI-H carcinomas subgroup. Based on intensive filtering, 57 known genes and eight ESTs were found to be highly relevant to the differentiation of MSI-H and MSS colorectal carcinomas. These genes successfully distinguish the new test set of six MSI-H and five MSS colorectal carcinomas. Many up- and downregulated genes in MSI-H colorectal carcinomas were related to the previously reported phenotypic characteristics; increased mucin production and intense peritumoral immune response in MSI-H carcinomas. Some of these differences were confirmed by semiquantitative reverse transcription-PCR and immunohistochemical analysis. Our findings indicate that there are many different genetic and transcriptomic characteristics between MSI-H and MSS colorectal carcinomas, and some of these differently expressed genes can be used as diagnostic or prognostic markers.

Microsatellite instability in colorectal carcinoma. The comparison of immunohistochemistry and molecular biology suggests a role for hMSH6 [correction of hMLH6] immunostaining.

Context Microsatellite instability (MSI) due to defective mismatch repair (MMR) genes has been reported in the majority of colorectal tumors from patients with hereditary nonpolyposis colorectal cancer syndrome and in 10% to 15% of sporadic colorectal cancers. The identification of cancers associated with MSI requires classical molecular testing as the gold standard. Objective The aim of this study was to evaluate the role of immunohistochemistry with antibodies directed against 4 MMR proteins as a screening tool for carcinomas with MSI. Methods In this study, 204 formalin-fixed, paraffin-embedded colorectal carcinomas were examined for MMR protein expression (hMLH1, hMSH2, hMSH6, and hPMS2) and analyzed for MSI (MSI-H indicates at least 2 of 6 markers affected). These results were correlated with histopathologic parameters. Results Immunohistochemical analysis revealed that loss of expression of at least 1 protein was present in 17% of cases. One hundred percent of carcinomas that showed high instability (MSI-H) showed loss of expression of hMLH1, hMSH2, or hMSH6. Loss of expression of 2 proteins was present in 59.4% of MSI-H cases, with only 2 combinations, namely, hMLH1/hPMS2 and hMSH2/hMSH6. Isolated loss of hMSH6 expression was present in 2 MSI-H cases. Conclusions These findings confirm that examination of MMR protein expression by immunohistochemistry is a simple method to diagnose colorectal cancer with MSI. Our data suggest that the study of hMSH6 may be useful, in addition to hMLH1 and hMSH2. Moreover, immunohistochemistry could represent a screening method with which to direct research on the mutations of MMR genes observed in hereditary nonpolyposis colorectal cancer syndrome.

Microsatellite instability in diagnostic pathology

A defect in the DNA mismatch repair process results in the phenomenon of microsatellite instability (MSI), which is the fundamental genetic alteration in a number of neoplastic conditions. This neoplastic pathway has been most widely studied in the setting of colorectal carcinoma. It is operative in both hereditary [hereditary non-polyposis colorectal carcinoma syndrome, (HNPCC)] and sporadic tumours. In both instances, tumours resulting from this molecular pathway may have important clinical differences in comparison to those resulting from the more common adenoma–carci-noma sequence/suppressor pathway. Patients with these tumours may have a survival advantage, and possibly a different response to commonly used chemotherapeutic agents. In addition, there are histopathological features which may aid in identification of these lesions. However, definite diagnosis requires molecular confirmation of the presence of MSI. Although precise in the diagnosis of MSI tumours, molecular testing requires specialized techniques and cannot be routinely performed in most diagnostic laboratories. Monoclonal antibodies have been recently developed identifying the expression of hMLH1, hMSH2, and other mismatch repair proteins. The expression of these proteins has been shown to correlate well with the existence of MSI in colorectal carcinomas, which allows the identification of MSI-associated tumours in a more rapid and cost-effective manner. This paper reviews the theoretical concept of MSI, and the clinicopathologic features of these tumours. In addition, the use and value of immunohistochemistry in this field is discussed.

Microsatellite instability in colorectal carcinoma

Microsatellite instability in colorectal carcinoma

Tumor‐infiltrating lymphocytes are a marker for microsatellite instability in colorectal carcinoma

Tumor‐infiltrating lymphocytes are a marker for microsatellite instability in colorectal carcinoma