Microsatellite instability in colorectal cancer: improved assessment using fluorescent polymerase chain reaction

P53 loss of heterozygosity (LOH) in formalin-fixed paraffin-embedded leiomyosarcoma (LMS): a novel report

BACKGROUND

The occurrence of p53 loss of heterozygosity (LOH) is a common genetic event in malignancy. LOH occurs when a heterozygous locus loses one of its two parental alleles, becoming homozygous at that locus, by either copy number loss (CNL-LOH) or by becoming copy number neutral (CNN-LOH). A role for CNL-LOH (cnLOH) has been postulated in cancer aetiology. Loss of heterozygosity (LOH) results in irreversible genetic loss.

AIMS

LOH was determined in DNA extracted from formalin-fixed paraffin-embedded (FFPE) leiomyosarcoma (LMS) specimens in a retrospective study from 30 patients, to assess the prognostic significance of LOH. The findings were analysed and their validity assessed. LOH was an adverse prognostic factor in LMS. Prospective uniform standardisation of formalin-fixation techniques is required.

METHODS

DNA was extracted from 169 formalin-fixed paraffin blocks of 30 patients with LMS, following extensive tissue microdissection. Genomic DNA was amplified using the polymerase chain reaction (PCR) technique. Fluorescence-based microsatellite PCR was used to detect and quantitate heterozygosity loss.

RESULTS

LOH was detected at gene locus 17p13 in 16 LMS (Four grade 2 and 12 grade 3 LMS). LOH was not detected in 14 LMS cases (one grade 1, five grade 2 and eight grade 3 LMS). LOH was associated with shorter patient survival.

CONCLUSIONS

The results reported herein endorse the value of utilizing FFPE DNA in identifying LOH as a prognostic factor in LMS. The results have implications for tumour biobanking and precision medicine in patients with sarcomas.

Microsatellite Instability Analysis (MSA) for Bladder Cancer: Past History and Future Directions

Microsatellite instability (MSI), the spontaneous loss or gain of nucleotides from repetitive DNA tracts, is a diagnostic phenotype for gastrointestinal, endometrial, colorectal, and bladder cancers; yet a landscape of instability events across a wider variety of cancer types is beginning to be discovered. The epigenetic inactivation of the MLH1 gene is often associated with sporadic MSI cancers. Recent next-generation sequencing (NGS)-based analyses have comprehensively characterized MSI-positive (MSI+) cancers, and several approaches to the detection of the MSI phenotype of tumors using NGS have been developed. Bladder cancer (here we refer to transitional carcinoma of the bladder) is a major cause of morbidity and mortality in the Western world. Cystoscopy, a gold standard for the detection of bladder cancer, is invasive and sometimes carries unwanted complications, while its cost is relatively high. Urine cytology is of limited value due to its low sensitivity, particularly to low-grade tumors. Therefore, over the last two decades, several new "molecular assays" for the diagnosis of urothelial cancer have been developed. Here, we provide an update on the development of a microsatellite instability assay (MSA) and the development of MSA associated with bladder cancers, focusing on findings obtained from urine analysis from bladder cancer patients as compared with individuals without bladder cancer. In our review, based on over 18 publications with approximately 900 sample cohorts, we provide the sensitivity (87% to 90%) and specificity (94% to 98%) of MSA. We also provide a comparative analysis between MSA and other assays, as well as discussing the details of four different FDA-approved assays. We conclude that MSA is a potentially powerful test for bladder cancer detection and may improve the quality of life of bladder cancer patients.

Molecular and Computational Methods for the Detection of Microsatellite Instability in Cancer

Microsatellite instability (MSI) is a genomic alteration in which microsatellites, usually of one to four nucleotide repeats, accumulate mutations corresponding to deletions/insertions of a few nucleotides. The MSI phenotype has been extensively characterized in colorectal cancer and is due to a deficiency of the DNA mismatch repair system. MSI has recently been shown to be present in most types of cancer with variable frequencies (from <1 to 30%). It correlates positively to survival outcome and predicts the response to immune checkpoint blockade therapy. The different methods developed for MSI detection in cancer require taking into consideration two critical parameters which influence method performance. First, the microsatellite markers used should be chosen carefully to ensure they are highly sensitive and specific for MSI detection. Second, the analytical method used should be highly resolute to allow clear identification of MSI and of the mutant allele genotype, and should present the lowest limit of detection possible for application in samples with low mutant allele frequency. In this review, we describe all the different molecular and computational methods developed to date for the detection of MSI in cancer, how they have evolved and improved over the years, and their advantages and drawbacks.

A genome-wide view of microsatellite instability: old stories of cancer mutations revisited with new sequencing technologies

Microsatellites are simple tandem repeats that are present at millions of loci in the human genome. Microsatellite instability (MSI) refers to DNA slippage events on microsatellites that occur frequently in cancer genomes when there is a defect in the DNA-mismatch repair system. These somatic mutations can result in inactivation of tumor-suppressor genes or disrupt other noncoding regulatory sequences, thereby playing a role in carcinogenesis. Here, we will discuss the ways in which high-throughput sequencing data can facilitate genome- or exome-wide discovery and more detailed investigation of MSI events in microsatellite-unstable cancer genomes. We will address the methodologic aspects of this approach and highlight insights from recent analyses of colorectal and endometrial cancer genomes from The Cancer Genome Atlas project. These include identification of novel MSI targets within and across tumor types and the relationship between the likelihood of MSI events to chromatin structure. Given the increasing popularity of exome and genome sequencing of cancer genomes, a comprehensive characterization of MSI may serve as a valuable marker of cancer evolution and aid in a search for therapeutic targets.

Quality assessment and correlation of microsatellite instability and immunohistochemical markers among population- and clinic-based colorectal tumors results from the Colon Cancer Family Registry

The detection of defective mismatch repair (MMR), as assessed by the presence of tumor microsatellite instability (MSI) and/or loss of MMR protein expression by IHC, has been useful for risk assessment, prognosis, and prediction of treatment in patients with colorectal cancer. We analyzed tumors for the presence of defective MMR from 5927 Colorectal Cancer Family Registry patients recruited at six international consortium sites. We evaluated the appropriate percentage instability cutoff used to distinguish the three MSI phenotypes [ie, stable (MSS), low instability (MSI-L), and high instability (MSI-H)]; the sensitivity, specificity, and performance characteristics of individual markers; and the concordance between MSI and IHC phenotypes. Guided by the results of the IHC testing, our findings indicate that the distinction between an MSI-H phenotype from a low-instability or MSS phenotype can best be accomplished by using a cutoff of 30% or greater of the markers showing instability. The sensitivity and specificity of the mononucleotide markers were higher than those of the dinucleotide markers. Specifically, BAT26 and BAT25 had the highest sensitivity (94%) and specificity (98%), and the use of mononucleotide markers alone identified 97% of the MSI-H cases correctly. As expected, the presence of MSI-H correlated with an older age of diagnosis, the presence of tumor in the proximal colon, and female sex.

Differences and evolution of the methods for the assessment of microsatellite instability

Microsatellite instability (MSI) originates from the systematic accumulation of uncorrected deletion/insertion in repetitive DNA tracts in cancer cells with a deficient mismatch repair system. Among colorectal cancers, the MSI signature identifies hereditary cases arising in patients with germline mutations in hMLH1, hMSH2, PMS2 and a fraction of those with hMSH6 mutations, as well as sporadic cancers with epigenetic hMLH1 promoter hypermethylation. Considering the specific pathogenesis, pathological features, natural history and response to 5-fluoro-uracil-based chemotherapy of the MSI cancers, confusion about the genetic markers for MSI recognition seems surprising. In this clinically relevant field, an agreement has not been reached concerning the use of di- or mononucleotide markers for MSI assessment. The Revised Bethesda Guidelines still recommend a panel of markers consisting of mono- and dinucleotides, despite being questioned whether it is congruous to continue to use dinucleotide markers for MSI identification. In any event, no single marker is accurate enough for MSI testing, and an awareness of their pros and cons is required for proper interpretation of results. In recent years, several papers have reported different prevalence of MSI in unrelated series, largely depending on the detection and classification method, suggesting that MSI test interpretation also requires the understanding of the phenomenon rather than simply the crude satisfaction of panel recommendations. Inaccuracies can otherwise lead to under- or overdiagnosis and inaccurate disease classification, which always have a negative impact on the clinical practice of medicine.

Sessile serrated adenoma: challenging discrimination from other serrated colonic polyps

Sessile serrated adenoma (SSA) is the proposed precursor for microsatellite unstable colorectal carcinomas and some authorities recommend that SSAs should be managed similar to adenomas. The aim of our study was to determine whether serrated polyps can be classified with sufficient consistency to support current treatment recommendations. One hundred eighty-five serrated polyps were classified as hyperplastic polyp (HP), SSA, or traditional serrated adenoma (TSA) by 5 pathologists blinded to clinical data. The observers documented which histologic features they considered most helpful in reaching their diagnosis in each case. In a second round, the observers were provided with polyp site and size. After reaching a consensus on minimum criteria for SSA and TSA, the pathologists classified another set of 50 polyps. The interobserver concordance was calculated using kappa statistics. In the first round, the overall interobserver agreement was moderate (kappa=0.55). Concordance for HP and SSA was moderate whereas it was nearly perfect for TSA. In the second round, there was no improvement in the concordance. All observers relied more often on architectural features than on cytologic ones to distinguish SSA from HP and agreement was reached that architectural features should provide the basis for the diagnosis of SSA. Subsequently, interobserver concordance was slightly improved but remained moderate (kappa=0.58). Interobserver agreement for the diagnosis of serrated polyps is moderate. However, this level of variability is acceptable because the presence of SSA indicates increased risk of developing additional serrated polyps and carcinoma, and surveillance is appropriate.

Assessment of microsatellite instability in colorectal carcinoma at an Indian center

AIM

The purpose of the present study was to evaluate the frequency of microsatellite instability (MSI) in colorectal cancers in an Indian cohort.

MATERIALS AND METHODS

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.

RESULTS

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.

CONCLUSION

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.

Comparison of three commonly used PCR-based techniques to analyze MSI status in sporadic colorectal cancer

Several retrospective studies have shown that a high level of microsatellite instability (MSI-H) is an important prognostic factor of a more favorable outcome in stage II and III colorectal cancer (CRC) patients. In this study, three commonly used polymerase chain reaction (PCR)-based MSI analysis techniques were compared (polyacrylamide gel electrophoresis followed by silver-staining [SSPAGE], fluorescence capillary electrophoresis [FCE], and denaturing high-performance liquid chromatography [DHPLC]) on a limited group of CRC patients, to identify the most optimal detection technique. Pathology blocks of 26 CRC patients were subjected to microdissection and the Bethesda reference panel was used for MSI analysis. Considering the samples analyzed by both SSPAGE and FCE, 8.7% were MSI-H, 8.7% were MSI-L, and 82.6% were MSS using SSPAGE. FCE resulted in 16% MSI-H, 4% MSI-L, and 80% MSS. Due to difficulties in analyzing the dinucleotide markers on DHPLC, we only analyzed the mononucleotide markers with this technique. The results were 100% concordant to those obtained by FCE. SSPAGE is time consuming, subjective, and less user-friendly and interpretable. DHPLC was not feasible due to interpretation difficulties for the dinucleotide markers. We recommend the use of FCE to analyze MSI status. This technique is sensitive, reproducible, user-friendly and leads to easy interpretation and high-throughput.

Enhanced detection of microsatellite instability and mismatch repair gene expression in cutaneous squamous cell carcinomas

BACKGROUND

Microsatellite instability (MSI) is a phenotypic characteristic of tumors with biallelic inactivation of mismatch repair genes, such as MSH2 or MLH1, and contributes to malignant transformation.

AIMS

The aim of this study was to examine the prevalence of MSI in cutaneous squamous cell carcinoma (SCC) using a PCR and fluorescent-based detection system. These methods of analysis offer several advantages over the use of silver staining and autoradiographic techniques. We also aimed to determine if MSI status correlated with expression of the MSH2 and MLH1 mismatch repair proteins in these cutaneous SCC samples.

METHODS

The MSI status of 22 histologically confirmed invasive cutaneous SCC samples were analyzed at five microsatellite markers (the National Cancer Institute's Bethesda panel of two mononucleotide and three dinucleotide markers) using a PCR and fluorescent-based detection system. Immunohistochemical analysis of MSH2 and MLH1 protein expression was also carried out on the SCC samples.

RESULTS

Only one case of cutaneous SCC displayed MSI. This was found at just one of five markers, and thus was low frequency MSI. All 22 cutaneous SCC cases strongly expressed MSH2 protein. Eighteen (82%) of the cutaneous SCC cases showed moderate to strong expression of MLH1 protein. The remaining four cases of cutaneous SCC were negative for MLH1 protein. Therefore, the majority of the SCC patients analyzed showed a correlation between absence of MSI and expression of MSH2 and MLH1 proteins.

CONCLUSIONS

MSI is uncommon in cutaneous SCC. In addition, MSH2 was strongly expressed in all SCC samples analyzed and appeared to be upregulated when compared with the corresponding normal tissue. MLH1 protein was not detected in 4 of 22 SCC cases, although it was expressed in the corresponding normal tissue, suggesting that inactivation of MLH1 may be a late event in a subset of invasive SCC cases.

Role of detection of microsatellite instability in Chinese with hereditary nonpolyposis colorectal cancer or ordinary hereditary colorectal cancer

AIM: To detect microsatellite instability (MSI) in patients with hereditary nonpolyposis colorectal cancer or ordinary hereditary colorectal cancer and to provide criteria for screening the kindreds with hereditary nonpolyposis colorectal cancer at molecular level.

METHODS: MSI was detected in the specimens from 20 cases with HNPCC, 20 cases with ordinary hereditary colorectal cancer and 20 cases with sporadic colorectal cancer by means of polymerase chain reaction-single strand conformation polymorphism.

RESULTS: The positive rate of MSI was 85% (17/20) in HNPCC group, 40% (8/20) in ordinary hereditary colorectal cancer group and 10% (2/20) in the sporadic colorectal cancer group respectively. The differences were significant. The mean ages of the three groups were 43.6, 52.2, and 61.8 years respectively, which increased gradually. The incidence of right hemicolon cancer was 64.7%, 37.5%, and 0% respectively, which decreased gradually and had significant difference. The expression ratio of BAT26 and BAT25 was 94.1% respectively, which was highest in the 5 gene sites studied. The incidence of poorly differentiated adenocarcinoma was 70.6% in HNPCC group among high frequency microsatellite instability (MSI-H), which was higher than the other two groups, which had 50% and 50% respectively.

CONCLUSION: The incidence of MSI-H is higher in HNPCC group. The detection of MSI is simple and economical and has high correlation with the clinicopathologic feature of HNPCC and can be used as a screening method to detect the germ line mutation of the mismatch repair gene.

Gene-gene, gene-environment & multiple interactions in colorectal cancer

This review comprehensively evaluates the influence of gene-gene, gene-environment and multiple interactions on the risk of colorectal cancer (CRC). Methods of studying these interactions and their limitations have been discussed herein. There is a need to develop biomarkers of exposure and of risk that are sensitive, specific, present in the pathway of the disease, and that have been clinically tested for routine use. The influence of inherited variation (polymorphism) in several genes has been discussed in this review; however, due to study limitations and confounders, it is difficult to conclude which ones are associated with the highest risk (either individually or in combination with environmental factors) to CRC. The majority of the sporadic cancer is believed to be due to modification of mutation risk by other genetic and/or environmental factors. Micronutrient deficiency may explain the association between low consumption of fruit/vegetables and CRC in human studies. Mitochondrial modulation by dietary factors influences the balance between cell renewal and death critical in colon mucosal homeostasis. Both genetic and epigenetic interactions are intricately dependent on each other, and collectively influence the process of colorectal tumorigenesis. The genetic and environmental interactions present a good prospect and a challenge for prevention strategies for CRC because they support the view that this highly prevalent cancer is preventable.

Microsatellite analysis of the APC gene and immunoexpression of E-cadherin, catenin, and tubulin in esophageal squamous cell carcinoma

The histological features that accompany the development and progression of solid tumors are known to be controlled by a distinct cascade of molecular events. One such event is the inactivation of tumor suppressor genes, such as the adenomatous polyposis coli (APC) gene. Disruption of the cadherin-catenin cell adhesion complex also plays a role in the initial steps of cancer invasion and metastasis whereas alterations in cell structural molecules, such as tubulin, may contribute to the cancer phenotype. The understanding of the status of these molecules in ESSC may provide novel markers that could impact on management of the disease. The present study examined alterations in the microsatellite sequence of the APC gene via fluorescent-based polymerase chain reaction in 100 cases of primary esophageal squamous cell carcinoma. In addition, the expression of E-cadherin, alpha- and beta-catenin, and alpha- and beta-tubulin was analyzed using immunohistochemistry. These data were then statistically compared with each other as well as the relevant clinicopathologic data. Although the APC markers (D5S210, D5S346, D5S299, and D5S82) tested did show an overall high frequency of allelic imbalance/loss of heterozygosity (62.48%) and microsatellite instability (41.27%), they did not show prognostic significance in the study cohort and were not correlated with the immunohistochemical data. The tubulin proteins showed no significant change in expression in the tumor tissue The decreased immunoreactivity of E-cadherin was statistically correlated with the presence of lymph node metastases (P = .0180). Although alpha- and beta-catenin as well as E-cadherin showed no direct prognostic value, E-cadherin may warrant further investigation as an indirect prognostic indicator by allowing more accurate prediction of lymph node metastases.

Microsatellite analysis of the adenomatous polyposis coli (APC) gene and immunoexpression of beta catenin in nephroblastoma: a study including 83 cases treated with preoperative chemotherapy

AIMS

To determine whether microsatellite mutations of the adenomatous polyposis coli (APC) gene have pathological or prognostic significance in nephroblastomas and to correlate APC alterations with beta catenin immunoexpression.

METHODS

One hundred nephroblastomas were analysed, 83 of which received preoperative chemotherapy. Normal and tumour DNA was isolated using standard proteinase K digestion and phenol/chloroform extraction from paraffin wax embedded tissue. Polymerase chain reaction using four APC microsatellite markers-D5S210, D5S299, D5S82, and D5S346-was performed and the products analysed. Immunohistochemistry was performed using the LSAB kit with diaminobenzidine as chromogen. Results were correlated with clinicopathological data using the chi(2) test.

RESULTS

Allelic imbalance/loss of heterozygosity was more frequent than microsatellite instability, with 30% of cases showing allelic imbalance/ loss of heterozygosity and 16% showing microsatellite instability. Although there was a significant correlation between the results for individual markers and the clinicopathological data, the overall results do not support a prognostic role for APC in nephroblastoma. Expression of beta catenin was seen in 93% of cases. Staining was predominantly membranous, with epithelium, blastema, and stroma being immunoreactive. Cytoplasmic redistribution was seen in 58% of cases, but no nuclear staining was detected. No significant associations between beta catenin expression and the clinicopathological parameters were found. Kaplan-Meier survival plots showed that patients with loss of membranous staining and pronounced cytoplasmic staining (score, 3) had a significantly shorter survival (p = 0.04; median survival, 5.87 months).

CONCLUSION

Microsatellite analysis of APC and immunoexpression of beta catenin did not provide significant pathological or prognostic information in this cohort of nephroblastomas.

Prognostic significance of microsatellite instability in curatively resected adenocarcinoma of the small intestine

Adenocarcinoma of the small intestine (ACSI) is a rare condition with few studies addressing follow-up and prognosis. Tumors of 35 patients with curative resection of an ACSI were retrospectively analyzed by immunohistochemistry: p53, hMLH1, hMSH2 and hMSH6 and microsatellite instability (MSI): BAT-26, BAX, TGF-beta RII. With a median follow up of 6.1 years, the median cancer-specific survival (CSS) was 36.2 months. Patients who were highly instable (MSI-H) (n=10) had a CSS of 49.6 months in contrast to patients with stable tumors (23.2 months) (P=0.010). Additionally, a low tumor stage according to UICC and MSI-H were shown to be independent factors (P=0.005 and P<0.001) for an increased survival in multivariate analysis. Therefore, it is suggested that analysis of the MSI status might prove useful in discerning prognosis within cancers of the same stage.

Microsatellite analysis of the DCC gene in nephroblastomas: pathologic correlations and prognostic implications

Microsatellite instability has been reported in a wide variety of cancer types. Inactivation or loss of tumour suppressor genes has been shown to result in cell cycle deregulation and neoplastic growth. We conducted a microsatellite study using fluorescent-based DNA technology to determine whether mutations in the microsatellite sequences of the deleted in colorectal cancer (DCC) gene, a tumour suppressor at 18q21.1, have any pathologic correlation or prognostic significance in nephroblastomas. Normal and tumour DNA was isolated from 106 cases of nephroblastoma using the standard proteinase K digestion and phenol-chloroform extraction method from paraffin wax-embedded tissue. Polymerase chain reaction using three microsatellite markers; D18S21, D18S34 and D18S58, for the DCC gene were performed. The polymerase chain reaction products were analysed on the ALF Express Automated DNA sequencer. The results were correlated with age at diagnosis, preoperative chemotherapy, clinicopathological stage, histological classification and patient outcome using chi(2) test. Allelic imbalance/loss of heterozygosity appeared to be a more frequent genetic aberration than microsatellite instability with 20% of cases showing allelic imbalance/loss of heterozygosity and only 9% of cases showing microsatellite instability. Genetic aberrations were more frequent in unfavourable histology tumours compared to favourable histology tumours (P=0.012). All patients with genetic aberrations for more than one DCC marker died independent of histological classification and stage (P=0.016). There was no statistically significant difference when DCC aberrations were compared with age at diagnosis, preoperative chemotherapy and clinicopathological stage. In conclusion, this study has found that multiple aberrations involving the DCC locus may play a role in the progression of nephroblastomas, and hence confer a poorer prognosis.

Cell kinetics and genetic instabilities in differentiated type early gastric cancers with different mucin phenotype

To clarify the biological impact and molecular pathogenesis of cellular phenotype in differentiated-type gastric cancers (DGCs), we investigated cell kinetics and genetic instabilities in early stage of DGCs. A total of 43 early gastric cancers (EGCs) were studied. EGCs were divided into 3 phenotypic categories: gastric (G type, n = 11), ordinary (O type, n = 20), and complete intestinal (CI type, n = 12) based on the combination of HGM, ConA, MUC2, and CD10. Proliferative index (PI), apoptotic index (AI), and p53 overexpression were investigated by immunohistochemical staining with anti-Ki-67, the terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick-end labeling method, and p53 antibody, respectively. Using a high-resolution fluorescent microsatellite analysis system, microsatellite instability (MSI) and loss of heterozygosity (LOH) were examined. Frameshift mutation analysis of transforming growth factor-beta type II receptor (TGF-betaRII) and bcl-2-associated X (BAX) in cancers with MSI was also performed. The mean AI/PI ratio values were 0.04 for G-type, 0.10 for O-type, and 0.13 for CI-type cancers--significantly lower in G type than in O and CI types (P = 0.02 and P = 0.001, respectively). No difference in the incidence of MSI and LOH was seen among the 3 cellular phenotypes. However, the major pattern of MSI, which showed drastic and widely dispersed changes and is related to an increased risk for cancer, was significantly higher in G and O types than in CI type (P <0.005). No frame shift mutations of TGF-betaRII or BAX were found in CI-type cancers. These results indicate that G-type cancers are likely to show more aggressive behaviors than CI-type cancers, and that O-type cancers show the intermediate characteristics of both types. However, the molecular pathogenesis of each phenotypic cancer is not associated with microsatellite alterations.

Very low incidence of microsatellite instability in intraductal papillary-mucinous neoplasm of the pancreas

Intraductal papillary-mucinous carcinoma (IPMC) of the pancreas, a new entity of pancreatic cancer with a favorable prognosis, has shown a gradual increase in the number of reported cases. Patients with high-frequency microsatellite instability (MSI-H) tumors have been shown to survive longer than those with low-frequency MSI (MSI-L) or microsatellite stable (MSS) tumors in colorectal and gastric cancer. We investigated whether MSI-H in patients with IPMC can contribute to a good prognosis. The formalin-fixed paraffin-embedded tumors and surrounding normal pancreatic tissues from 10 patients with IPMCs and 16 with intraductal papillary-mucinous adenomas (IPMAs) were provided for DNA extraction after microdissection. Polymerase chain reaction (PCR) was carried out using 8 microsatellite primer marker sets. The mixed PCR samples were analyzed using a genetic analyzer. MSI-H was determined by assessment of microsatellite variations in 3 or more of the 8 tested markers. Immunohistochemical staining of the MSI-responsible proteins hMLH1 and hMSH2 was conducted for both the IPMC and IPMA samples. Ten percent of IPMC harbored MSI-H tumors, whereas no MSI-H tumors were detected in the IPMAs. Thirty percent of IPMC tumors and 25% of IPMA tumors showed MSI-L. All IPMCs and IPMAs showed normal expression of both hMLH1 and hMSH2. MSI-H and loss of hMLH1 and hMSH2 are very rare events in both IPMCs and IPMAs. We conclude that a good prognosis for patients with IPMC is not associated with MSI-H.

Evaluation of tumor microsatellite instability using five quasimonomorphic mononucleotide repeats and pentaplex PCR

BACKGROUND & AIMS

The microsatellite instability (MSI) phenotype is a characteristic of the hereditary nonpolyposis colorectal cancer syndrome as well as approximately 15% of sporadic colon and gastric tumors. It is a valuable diagnostic marker for the identification of hereditary nonpolyposis colorectal cancer cases and may be a molecular predictive marker for the identification of colon cancer patients who benefit from chemotherapy. To evaluate MSI, a reference panel was proposed at an international consensus meeting, comprised of 2 mononucleotide (BAT-25, BAT-26) and 3 dinucleotide repeats. Analysis of BAT-26 is sufficient for detecting the MSI phenotype in most, but not all, cases. Additional results with dinucleotide markers can sometimes lead to incorrect classification of MSI tumors.

METHODS

We describe here a single fluorescent multiplex system comprising 5 quasimonomorphic mononucleotide repeats for the detection of MSI tumors.

RESULTS

None of 184 germline DNA samples, including 56 from African subjects, was found to contain allelic size variations in more than 2 of these markers. In contrast, all MSI tumors showed allelic size variations in 3 or more of the microsatellites. Using this assay, we confirmed (or reclassified in 6 cases) the MSI status of 124 colon and 50 gastric primary tumors and 16 colon cell lines.

CONCLUSIONS

We propose that using a pentaplex polymerase chain reaction system allows accurate evaluation of tumor MSI status of DNA with 100% sensitivity and specificity without the need to match normal DNA. This assay is simpler to use than those involving dinucleotides and is more specific than using BAT-26 alone.

Prognostic implications of BAX and TGFBRII mutations in colon cancers with microsatellite instability

Microsatellite instability in sporadic colon cancer is associated with an improved prognosis. Recent studies, however, have suggested that microsatellite unstable cancers with mutations in the proapoptotic gene BAX have a relatively poor prognosis, whereas those with mutations in transforming growth factor-beta receptor type II (TGFBRII) have a relatively good prognosis. Using instability in the non-coding mononucleotide repeat BAT-26 as a measure of generalized microsatellite instability, we evaluated the prognosis of unstable colon cancers with and without frameshift mutations in the coding mononucleotide repeats of BAX and TGFBRII in a population-based sample of 1,427 individuals. BAX mutations were identified in 39.0% (64/164) of unstable colon cancers, whereas TGFBRII mutations were identified in 79.3% (138/174) of unstable colon cancers. Unstable colon cancers with and without instability in BAX and TGFBRII were associated with very similar and statistically indistinguishable percentage 5-year survivals and Kaplan-Meier survival curves; stable colon cancers were associated with a significantly worse 5-year survival and Kaplan-Meier survival (P < 0.001 and P < 0.013, respectively, compared against BAT-26 unstable). The age- and stage-adjusted risk of death associated with BAX or TGFBRII mutations was not significantly different from that of unstable tumors without such mutations. We conclude that instability-induced mutations in BAX or TGFBRII do not have a significant impact on the good prognosis of colon cancers with microsatellite instability.

A high-resolution allelotype of B-cell chronic lymphocytic leukemia (B-CLL)

The most frequent chromosomal aberrations in B-cell chronic lymphocytic leukemia (B-CLL) are deletions on 13q, 11q, and 17p, and trisomy 12, all of which are of prognostic significance. Conventional cytogenetic analysis and fluorescence in situ hybridization (FISH) are used for their detection, but cytogenetic analysis is hampered by the low mitotic index of B-CLL cells, and FISH depends on accurate information about candidate regions. We used a set of 400 highly informative microsatellite markers covering all chromosomal arms (allelotyping) and automated polymerase chain reaction (PCR) protocols to screen 46 patients with typical B-CLL for chromosomal aberrations. For validation, we compared data with our conventional karyotype results and fine mapping with conventional single-site PCR. All clonal cytogenetic abnormalities potentially detectable by our microsatellite PCR (eg, del13q14 and trisomy 12) were picked up. Allelotyping revealed additional complex aberrations in patients with both normal and abnormal B-CLL karyotypes. Aberrations detectable in the samples with our microsatellite panel were found on almost all chromosomal arms. We detected new aberrant loci in typical B-CLL, such as allelic losses on 1q, 9q, and 22q in up to 25% of our patients, and allelic imbalances mirroring chromosomal duplications, amplifications, or aneuploidies on 2q, 10p, and 22q in up to 27% of our patients. We conclude that allelotyping with our battery of informative microsatellites is suitable for molecular screening of B-CLL. The technique is well suited for analyses in clinical trials, it provides a comprehensive view of genetic alterations, and it may identify new loci with candidate genes relevant in the molecular biology of B-CLL.

Distinction between familial and sporadic forms of colorectal cancer showing DNA microsatellite instability

Attempts to classify colorectal cancer into subtypes based upon molecular characterisation are overshadowed by the classical stepwise model in which the adenoma-carcinoma sequence serves as the morphological counterpart. Clarity is achieved when cancers showing DNA microsatellite instability (MSI) are distinguished as sporadic MSI-low (MSI-L), sporadic MSI-high (MSI-H) and hereditary non-polyposis colorectal cancer (HNPCC). Divergence of the 'methylator' pathway into MSI-L and MSI-H is at least partly determined by the respective silencing of MGMT and hMLH1. Multiple differences can be demonstrated between sporadic and familial (HNPCC) MSI-H colorectal cancer with respect to early mechanisms, evolution, molecular characterisation, demographics and morphology. By acknowledging the existence of multiple pathways, rapid advances in the fields of basic and translational research will occur and this will lead to improved strategies for the prevention, early detection and treatment of colorectal cancer.

A genome-wide study of microsatellite instability in advanced gastric carcinoma

BACKGROUND

Microsatellite instability (MSI) has been described in many human carcinomas, including gastric carcinomas (GCs). There are inconsistent findings regarding the association of MSI with various subsets of GC with specific clinicopathologic features. The objective of this study was to define MSI in advanced GC at a genome-wide level and to evaluate the clinical relevance of MSI in these patients.

METHODS

Forty-one gastric adenocarcinomas with serosa invasion (T3) were analyzed at 59 loci that detected at least one site per arm of each autosome in human genome. The expression patterns of mismatch repair proteins hMLH1 and hMSH2 were examined by immunohistochemistry. Comparisons were made by categorizing tumors into three groups: tumors with MSI at multiple loci (at more than three loci), tumors with MSI at low level (at one to three loci), and microsatellite-stable (MSS) tumors. Clinical significance of MSI in advanced GC was evaluated. The relative rates of hypermutability of the 59 markers also were determined.

RESULTS

A significant association was found between tumors with MSI at multiple loci and the expanding type of tumor growth by Ming's histologic classification (P = 0.001), whereas tumors with MSI at low level and MSS tumors are clinicopathologically indistinguishable. The 59 dinucleotide repeat markers displayed varying degrees of susceptibility toward genetic instability. The relative rates of hypermutability of these markers were consistent with a normal distribution pattern in which the frequency of unstable tumors detected at different chromosomal loci varied from 0% to 20%.

CONCLUSIONS

The authors' results showed that advanced GC with MSI at multiple loci progress preferentially in an expanding mode, supporting the notion that high MSI tumors and low MSI/MSS tumors evolve through different genetic pathways. Thus, microsatellite testing may have clinical utility as a favorable prognostic marker.

PCR techniques for clonality assays

Clonal overgrowths represent the hallmark of neoplastic proliferations, and their demonstration has been proved useful clinically for the diagnosis of malignant lymphomas based on the detection of specific and dominant immunoglobulin and/or T-cell receptor gene rearrangements. Nonrandom genetic alterations can also be used to test clonal expansions and the clonal evolution of neoplasms, especially analyzing hypervariable deoxyribonucleic acid (DNA) regions from patients heterozygous for a given marker. These tests rely basically on the demonstration of loss of heterozygosity (LOH) resulting from either hemizygosity (nonrandom interstitial DNA deletions) or homozygosity of mutant alleles observed in neoplasms. LOH analyses identify clonal expansions of a tumor cell population, and point to monoclonal proliferation when multiple and consistent LOH are demonstrated. Based on the methylation-related inactivation of one X chromosome in female subjects, X-linked markers (e.g., androgen receptor gene) will provide clonality information using LOH analyses after DNA digestion with methylation-sensitive restriction endonucleases. Therefore, both non-X-linked and X-linked analyses give complementary information, related and not related to the malignant transformation pathway respectively. Applied appropriately, these tools can establish the clonal evolution of tumor cell populations (tumor heterogeneity), identify early relapses, distinguish recurrent tumors from other metachronic neoplasms, and differentiate field transformation from metastatic tumor growths in synchronic and histologically identical neoplasms.

The instability within: problems in current analyses of microsatellite instability

Microsatellite instability is regarded as one of the phenotypes of defective DNA mismatch repair and, consequently, as a marker of high risk for cancer. Despite numerous studies, the reported rates for positive microsatellite instability differ widely in each human malignancy. These discrepancies may relate to problems in the methods used. To establish a methodology for an accurate microsatellite instability analysis, technical requirements for a precise assay and biological conditions required for positive microsatellite instability were discussed. First, to describe microsatellite changes in detail, a sensitive detection system with linear detection characteristics and electrophoresis with standardised migration and minimised migration errors are considered to be necessary. Therefore, systems using fluorescent labelling and laser scanning are recommended. For reproducible polymerase chain reactions, it is essential to control the terminal deoxynucleotidyl transferase activity in Taq polymerase. Second, as a biological condition for positive microsatellite instability, feasible selection and combination of microsatellite markers, mutations in specific DNA mismatch repair genes and existence of monoclonal populations enriched sufficiently in a sample are essential. Finally, one possible diagnostic criterion for positive microsatellite instability is proposed, that is the existence of one of the patterns shown in the panel (see Fig. 6) at one or more loci in a set of more than five microsatellite markers.

Sporadic colorectal adenocarcinomas with high-frequency microsatellite instability

BACKGROUND

Widespread microsatellite instability (MSI) occurs in nearly 15% of sporadic colorectal cancers. Large bowel carcinomas with high-frequency MSI (MSI-H) (instability at > or = 30% of microsatellite loci) are believed to display distinctive pathologic features and to behave less aggressively than microsatellite-stable (MSS) tumors and carcinomas with low-frequency MSI (MSI-L) (instability at < 30% of microsatellite loci). The aim of the current study was to accurately define the clinicopathologic and biologic features of MSI-H sporadic colorectal carcinomas.

METHODS

MSI status was evaluated in 216 large bowel adenocarcinomas using polymerase chain reaction (PCR) and 6 microsatellite markers. Tumors that showed instability with at least two microsatellite markers were classified as MSI-H, whereas the other tumors were classified as MSI-L (instability at one locus) or MSS (no instability). Expression of p53, hMLH1, and hMSH2 gene products was determined by immunohistochemistry, and DNA ploidy pattern was determined by flow cytometry. The prognostic significance of MSI status was assessed by univariate and multivariate survival analyses.

RESULTS

The significantly different pathologic features of MSI-H carcinomas were proximal location; large size; mucinous and medullary histotype; poor differentiation; expanding pattern of growth; more frequent Crohn-like conspicuous lymphoid reaction; and low incidence of extramural vein invasion. Most MSI-H tumors were DNA diploid (33 of 40 tumors; 82.5%) and p53 negative (34 of 44 tumors; 77.3%). Conversely, DNA aneuploidy and p53 overexpression were observed in 82.3% (130 of 158 tumors; P < 0.0001) and 54.1% (93 of 172 tumors; P = 0.0002) of MSI-L/MSS tumors, respectively. Loss of hMLH1 or hMSH2 expression was detected in a high fraction of MSI-H carcinomas (86. 0%). Patients with MSI-H tumors showed a better clinical outcome than patients with MSI-L/MSS tumors (P = 0.0017). Furthermore, in multivariate analysis that included conventional clinicopathologic parameters, MSI status, and p53 expression as covariates, MSI status was a significant independent prognostic indicator of disease specific survival.

CONCLUSIONS

Assessment of MSI status is an essential step in the genetic characterization of large bowel carcinomas and identifies a subset of tumors with distinct clinical, pathologic, and biologic features.

A comparative microsatellite analysis of colorectal cancer in patients <35 years and >50 years of age

OBJECTIVE

This study was undertaken to investigate microsatellite instability and allelic imbalance in a cohort of young patients (<35 yr) and older patients (>50 yr) with sporadic colorectal carcinomas in the Kwa-Zulu Natal region of South Africa.

METHODS

Normal and tumor DNA was isolated from formalin-fixed, paraffin-embedded tissue from 32 patients <35 yr and from 50 patients >50 yr of age. Tumors were staged using the modified Astler-Coller classification. Fluorescent-based DNA technology using an automated DNA sequencer (Alf Express Automated DNA Sequencer) was employed. CY5 labeled primers for microsatellite markers in chromosomes 18, 3, and 2 (DCC, D18S34, D18S58, D3S659, D3S1255, and D2S123) were used. The data were captured and analyzed using the Fragment Manager Software.

RESULTS

The informativity of the microsatellite markers ranged from 50% to 71.8%. Microsatellite instability was seen in 44 of 82 cases (53.7%) for at least one of the six markers. Low frequency MSI (MSI-L) was seen in 28 of 82 cases (34.2%) and high frequency MSI (MSI-H) in 16 of 82 cases (19.5%). In the <35-yr age group, MSI-L was seen in six cases (18.8%) and MSI-H in 10 cases (31.3%). In the >50 yr age group, MSI-L was seen in 22 cases (44%) and MSI-H in six cases (12%). Twelve cases showed AI for DCC, seven showed AI for D18S34, and four showed AI for D18S58. MSI was found in 13, 10, and 16 cases for each of these markers, respectively. Allelic imbalance for the D3S659, D2S123, and D3S1255 loci was 3 of 82 cases (3.7%), 10 of 82 cases (12.2%), and 13 of 80 cases (16.3%), respectively. MSI was 14.6% for both D3S659 and D2S123 and was 6.3% for the D3S1255 marker.

CONCLUSIONS

Loss of heterozygosity in the region of the DCC locus ranged from 9.3% to 26.7%, and MSI ranged from 12.2% to 19.5% of cases. Allelic imbalance in the region of the repair genes ranged from 6.8% to 27% in the informative cases. MSI, however, ranged from 5% to 12%. These figures are similar to those of other studies done in other parts of the world. Further, no correlation was found between the genetic results and clinicopathological parameters: i.e., tumor stage, grade and clinical parameters of age and gender. However, genetic abnormalities were more common in the younger cohort of patients, and this may translate into the earlier age of presentation. This opens the potential for genetic screening.

Hyperplastic polyps and DNA microsatellite unstable cancers of the colorectum

Although the scientific and clinical rationale for classifying colorectal cancer according to mechanisms underlying genetic instability is well supported, little is known of the early morphogenesis of sporadic cancer showing high levels of DNA microsatellite instability (MSI-H). Evidence is accumulating that the traditional adenoma-carcinoma sequence may not apply to sporadic MSI-H colorectal cancer. The serrated pathway comprising hyperplastic polyps, mixed polyps and serrated adenomas may serve as the missing link. This review relates the recently described CpG island methylator phenotype (CIMP) to the serrated pathway. Two rate-limiting genetic steps may underlie the neoplastic pathway associated with CIMP. A transmembrane receptor expressed by pericryptal myofibroblasts (HPP1) may be implicated in the transition from normal to hyperplasia whereas inactivation of hMLH1 is responsible for the conversion of hyperplasia to dysplasia through loss of DNA mismatch repair. These mechanisms fit with clinical observations relating to sporadic MSI-H colorectal cancer, specifically proximal location, multiplicity, higher frequency among females and rapid evolution of early cancer.

Microsatellite instability is a favorable prognostic indicator in patients with colorectal cancer receiving chemotherapy

BACKGROUND & AIMS

Adjuvant 5-fluorouracil (5-FU)-based chemotherapy is standard treatment for stage C colorectal cancer (CRC). Approximately 12% of CRCs are characterized by microsatellite instability (MSI), a hallmark of a DNA mismatch repair defect. We investigated the safety of adjuvant 5-FU-based chemotherapy for MSI(+) CRC and compared the prognosis of MSI(+) and MSI(-) CRC patients receiving adjuvant therapy.

METHODS

Previously, a prospective series consisting of 1044 consecutive CRCs has been collected and the MSI status of each sample determined. Patients with stage C cancer who had received adjuvant chemotherapy (n = 95) were followed up for 7-63 months (median, 31 months) after surgery.

RESULTS

No unexpected or serious adverse effects were observed when 5-FU-based chemotherapy was used as adjuvant treatment for MSI(+) CRC. Three- year recurrence-free survival was 90% and 43% in the MSI(+) (n = 11) and MSI(-) (n = 84) groups, respectively (P = 0.020).

CONCLUSIONS

Adjuvant 5-FU-based chemotherapy is feasible for both MSI(+) and MSI(-) CRCs, and patients with MSI(+) CRC who receive adjuvant therapy have an excellent prognosis.

Low frequency of replication errors in primary nervous system tumours

OBJECTIVES

Automated DNA technology was used to analyze the incidence of microsatellite instability (MIN) among the most frequent types of adult primary CNS tumours and to determine its relation with clinicopathological characteristics.

METHODS

Fifty six gliomas, 32 meningiomas and 11 schwannomas were screened for size changes at eight microsatellite loci using fluorescent polymerase chain reaction (PCR) followed by fragment analysis in an automated sequencer. A tumour was considered as MIN+ when a different electrophoretic pattern between constitutional and tumour DNA was evidenced in one or more microsatellite markers and as replication error positive (RER+) when at least 25% of the markers analyzed (2/8) showed instability. The MIN phenotype was correlated with relevant clinical and pathological parameters.

RESULTS

Globally, instability was found in 19/767 analyses (2.47%), with a higher rate among tetranuceotide than dinucleotide repeats (chi(2) test, p=0.018). Ten gliomas (17.9%), two meningiomas (6.3%), and two schwannomas (18.2%) were MIN+, whereas one glioma (1.8%), two meningiomas (6.3%), and one schwannoma (9.1%) were classified as RER+. A possible association between microsatellite instability and a shorter duration of clinical course was found in meningiomas. The MIN+ phenotype was more frequent in spinal than intracranial schwannomas (Fisher's exact test, p=0.018). No other significant association with clinical or histological features was detected.

CONCLUSIONS

Although microsatellite instability can be demonstrated at a low rate in some primary CNS tumours, a true replication error phenotype (revealed by widespread microsatellite instability at numerous loci) is uncommon and unlikely to play an important part in the pathogenesis of these neoplasms. This form of instability was more frequent in tetranucleotide than in dinucleotide repeats. To our knowledge, this is the first report of MIN in schwannomas, where it was associated with the spinal localisation of the tumour.

Microsatellite instability is not a defining genetic feature of acute myeloid leukemogenesis in adults: results of a retrospective study of 132 patients and review of the literature

The frequency of acute leukemia in children with constitutional DNA repair defects implicates defective DNA repair in leukemogenesis. Whether sporadic cases of AML also arise from an inherited genetic predisposition remains to be determined. Prior studies have reported microsatellite instability (MSI) in AML, particularly secondary and relapsed AML. These studies included small numbers of cases in which key features such as cytogenetic abnormalities were not reported. To determine whether defective DNA mismatch repair, reflected by MSI, is a defining feature of adult myeloid leukemogenesis, we retrospectively studied 132 AML cases including 28 de novo, 62 secondary, 22 relapsed/refractory, 15 cases of paired diagnosis/relapse. 110 patients were elderly (55+ years). The cases included a range of cytogenetic abnormalities. MSI was assessed at three loci (BAT 25, BAT 26, BAT 40) in DNA isolated from sorted leukemic blasts and paired T cell controls. Fluoresceinated PCR products were analyzed using an automated capillary electrophoresis system. Of the 132 AML cases, no single case demonstrated MSI. Our studies indicate that MSI, and defective DNA mismatch repair, is not a defining feature of the majority of adult patients with AML. Furthermore, our data does not support the hypothesis that MSI could be acquired during the progression of AML from diagnosis to relapse, as a consequence of therapeutic exposure.

Assessing microsatellite instability with semiautomated fluorescent technology: application to the analysis of primary brain tumors

The replication error phenotype, revealed by the observation of widespread microsatellite instability (MIN), has been identified as a new mechanism of cancer susceptibility, and the comparison of the allele sizes of polymorphic microsatellite repeats between normal and tumor DNA is now frequently undertaken in colorectal and other human neoplasias. The lack of precise characterization of the electrophoretic profiles of microsatellites is one of the main sources of discord between the rate of MIN reported for the same type of tumor by different investigators. The recent introduction of fluorescent-based semiautomated microsatellite analysis allows a more accurate size comparison, but one or more artificial peaks, generated during polymerase chain reaction (PCR) and/or electrophoresis, are frequently detected along with the true allele peaks. The aim of this study was to characterize the most frequent artificial extra peaks in the short tandem repeats (STRs) used by us to assess MIN in human cancers. We analyzed eight microsatellite loci in 113 primary brain tumors. HumFibra/FGA exhibited the most frequent extra peak formation. For each microsatellite there is a characteristic pattern of artifact formation which must be recognized to avoid a false-positive diagnosis of MIN.

Human leukocyte antigen class I gene mutations in cervical cancer

BACKGROUND

Various mechanisms contribute to the loss of human leukocyte antigen (HLA) class I expression that is frequently observed in cancers. Although some single allele losses have been ascribed to mutations in HLA class I genes, direct evidence for this phenomenon in vivo is still lacking. Thus, we investigated whether HLA class I gene mutations could account for the loss of allele-specific expression in cervical carcinomas.

METHODS

We used polymerase chain reaction-based techniques, including sequencing, oligonucleotide hybridization, and microsatellite analysis, to identify HLA class I gene defects in two tumor-derived cell lines and to confirm the presence of these defects in the original tumors.

RESULTS

In one tumor, in exon 2 of the HLA-B15 gene, a four-nucleotide insertion resulted in a stop codon in exon 3. In the other tumor, in two duplicated copies of the HLA-A24 gene, single-point mutations resulted in stop codons in exons 2 and 5.

CONCLUSIONS

To our knowledge, this is the first report of HLA class I gene mutations identified in primary tumors that lead to loss of allelic expression in tumor cells. Such tumor-specific mutations may permit the cell to escape HLA class I-restricted cytotoxic T-cell responses.

Allelic imbalance and microsatellite instability in chromosomes 2p, 3p, 5q, and 18q in esophageal squamous carcinoma in patients from South Africa

Microsatellite polymerase chain reaction (PCR) and fluorescent DNA technology was used to assess allelic imbalance (AI) or loss of heterozygosity (LOH) and microsatellite instability (MSI) in chromosomes 2p, 3p, 5q, and 18q in esophagectomy specimens from 39 patients who had squamous carcinoma and who lived in a high-incidence geographic location in South Africa. The squamous carcinomas were graded by conventional light microscopy and staged using the tumor-node-metastasis (TNM)-Union Internationale Contre Le Cancer (UICC) criteria. The DNA was isolated using proteinase K digestion and standard phenol-chloroform extraction procedure. Microsatellite PCR was performed using fluorescent, CY5-labeled primers for the following markers: D2S123 (2p), D3S659 (3p), D3S1255 (3p), D5S346 (5q), DCC (18q), D18S34 (18q), and D18S58 (18q). These markers were chosen because they are the most frequently used and most informative markers for these particular gene loci. Results were analyzed using software attached to an automated DNA sequencer. Molecular changes obtained were correlated with clinicopathologic parameters. Molecular analysis did not correlate with clinicopathologic features, such as tumor grade, stage, or lymph node status. No correlation with patient outcome was seen, though only limited follow-ups were obtained. Rates of MSI and LOH on 3p and 18q in these specimens are similar to the range seen in studies from other geographic areas. However, a striking point of departure is the high LOH (30% of informative cases) seen on 2p.

Microsatellite instability and 8p allelic imbalance in stage B2 and C colorectal cancers

BACKGROUND

Microsatellite instability (MSI) and allelic imbalance involving chromosome arms 5q, 8p, 17p, and 18q are genetic alterations commonly found in colorectal cancer. We investigated whether the presence or absence of these genetic alterations would allow stratification of patients with Astler-Coller stage B2 or C colorectal cancer into favorable and unfavorable prognostic groups.

METHODS

Tumors from 508 patients were evaluated for MSI and allelic imbalance by use of 11 microsatellite markers located on chromosome arms 5q, 8p, 15q, 17p, and 18q. Genetic alterations involving each of these markers were examined for associations with survival and disease recurrence. All P values are two-sided.

RESULTS

In univariate analyses, high MSI (MSI-H), i.e., MSI at 30% or more of the loci examined, was associated with improved survival (P =.02) and time to recurrence (P =.01). The group of patients whose tumors exhibited allelic imbalance at chromosome 8p had decreased survival (P =.02) and time to recurrence (P =.004). No statistically significant associations with survival or time to recurrence were observed for markers on chromosome arms 5q, 15q, 17p, or 18q. In multivariate analyses, MSI-H was an independent predictor of improved survival (hazard ratio [HR] = 0.51; 95% confidence interval [CI] = 0.31-0.82; P =.006) and time to recurrence (HR = 0.42; 95% CI = 0.24-0.74; P =.003), and 8p allelic imbalance was an independent predictor of decreased survival (HR = 1.89; 95% CI = 1.25-2.83; P =. 002) and time to recurrence (HR = 2.07; 95% CI = 1.32-3.25; P =.002).

CONCLUSIONS

Patients whose tumors exhibited MSI-H had a favorable prognosis, whereas those with 8p allelic imbalance had a poor prognosis; both alterations served as independent prognostic factors. To our knowledge, this is the first report of an association between 8p allelic imbalance and survival in patients with colorectal cancer.

Shortened microsatellite d(CA)21 sequence down-regulates promoter activity of matrix metalloproteinase 9 gene

One characteristic elements in the promoter of the matrix metalloproteinase 9 (MMP-9) gene is the d(CA) repeat. To investigate whether this element regulates the transcription of the MMP-9 gene and its enzymatic activities, we sequenced the promoter region isolated from esophageal carcinoma cell lines. TE9 cells with low MMP-9 enzymatic activity had the number of d(CA) repeats shortened from 21 to 14 or 18. TE8, TE10 and TE11 cells with high MMP-9 activities had 21 or 23 d(CA) repeats. Luciferase assays using MMP-9 promoter containing 18, 14 or 0 d(CA) repeats showed transcriptional activities which were 50, 50 or 5%, respectively, of the level achieved with promoter containing 21 d(CA) repeats. Sequence analysis of the promoter of 223 Japanese subjects revealed that most had two alleles with 20, 21 or 22 d(CA) repeats, whereas six had one or two alleles with 14, 18 or 19 d(CA) repeats. We postulate that length alteration of the d(CA) repeat causes phenotypic differences among carcinoma cells and that microsatellite instability may contribute to the polymorphism of d(CA) repeat length.