Molecular screening for the Lynch syndrome--better than family history?

Universal tumor screening for Lynch syndrome: health-care providers' perspectives

PURPOSE

Population-based reflex testing of colorectal tumors can identify individuals with Lynch syndrome (LS), but there is debate regarding the type of patient discretion such a program warrants. We examined health-care providers' views and experiences to inform the design of a reflex-testing program and their perspectives regarding an opt-out option.

METHODS

We interviewed providers managing LS or colorectal cancer patients, including surgeons, genetic counselors, oncologists, primary-care physicians, and gastroenterologists. Qualitative data were analyzed thematically using constant comparison techniques.

RESULTS

Providers supported a reflex-testing program because of the current lack of coordinated immunohistochemistry (IHC) testing and underascertainment of LS patients as well as the opportunity to standardize the increasing use of genomic tests in practice. Most supported an opt-out after reflex testing because they felt that IHC is akin to other pathology tests, which are not optional. Some favored an opt-out before testing because of concern for patients experiencing distress, insurance discrimination, or a diagnostic odyssey that may be inconclusive.

CONCLUSION

Providers support a reflex-testing program to improve the identification and management of suspected LS patients. However, how to support meaningful information provision to enable an opt-out without jeopardizing testing uptake and the anticipated public health benefits remains a policy challenge.Genet Med advance online publication 06 October 2016.

Mismatch repair defects and Lynch syndrome: The role of the basic scientist in the battle against cancer

We have currently entered a genomic era of cancer research which may soon lead to a genomic era of cancer treatment. Patient DNA sequencing information may lead to a personalized approach to managing an individual's cancer as well as future cancer risk. The success of this approach, however, begins not necessarily in the clinician's office, but rather at the laboratory bench of the basic scientist. The basic scientist plays a critical role since the DNA sequencing information is of limited use unless one knows the function of the gene that is altered and the manner by which a sequence alteration affects that function. The role of basic science research in aiding the clinical management of a disease is perhaps best exemplified by considering the case of Lynch syndrome, a hereditary disease that predisposes patients to colorectal and other cancers. This review will examine how the diagnosis, treatment and even prevention of Lynch syndrome-associated cancers has benefitted from extensive basic science research on the DNA mismatch repair genes whose alteration underlies this condition.

Familial colorectal cancer type X: genetic profiles and phenotypic features

Heredity is a major cause of colorectal cancer, but although several rare high-risk syndromes have been linked to disease-predisposing mutations, the genetic mechanisms are undetermined in the majority of families suspected of hereditary cancer. We review the clinical presentation, histopathologic features, and the genetic and epigenetic profiles of the familial colorectal cancer type X (FCCTX) syndrome with the aim to delineate tumor characteristics that may contribute to refined diagnostics and optimized tumor prevention.

Distinct gene expression signatures in lynch syndrome and familial colorectal cancer type x

Introduction

Heredity is estimated to cause at least 20% of colorectal cancer. The hereditary nonpolyposis colorectal cancer subset is divided into Lynch syndrome and familial colorectal cancer type X (FCCTX) based on presence of mismatch repair (MMR) gene defects.

Purpose

We addressed the gene expression signatures in colorectal cancer linked to Lynch syndrome and FCCTX with the aim to identify candidate genes and to map signaling pathways relevant in hereditary colorectal carcinogenesis.

Experimental design

The 18 k whole-genome c-DNA-mediated annealing, selection, extension, and ligation (WG-DASL) assay was applied to 123 colorectal cancers, including 39 Lynch syndrome tumors and 37 FCCTX tumors. Target genes were technically validated using real-time quantitative RT-PCR (qRT-PCR) and the expression signature was validated in independent datasets.

Results

Colorectal cancers linked to Lynch syndrome and FCCTX showed distinct gene expression profiles, which by significance analysis of microarrays (SAM) differed by 2188 genes. Functional pathways involved were related to G-protein coupled receptor signaling, oxidative phosphorylation, and cell cycle function and mitosis. qRT-PCR verified altered expression of the selected genes NDUFA9, AXIN2, MYC, DNA2 and H2AFZ. Application of the 2188-gene signature to independent datasets showed strong correlation to MMR status.

Conclusion

Distinct genetic profiles and deregulation of different canonical pathways apply to Lynch syndrome and FCCTX and key targets herein may be relevant to pursue for refined diagnostic and therapeutic strategies in hereditary colorectal cancer.

Familial colorectal cancer type X: polyp burden and cancer risk stratification via a family history score

BACKGROUND

Patients fulfilling Amsterdam-1 criteria without mismatch repair deficiency (termed familial colorectal cancer type X (FCC type X)) were reported to have lower cancer risks than classic Lynch syndrome. This study investigates the polyp and cancer burden of this population and demonstrates relationships with a family history score (FHS).

METHODS

The Jagelman Registry was queried for patients meeting Amsterdam criteria with microsatellite stable/low colorectal cancers. The risk of colorectal neoplasia was ascertained using a published FHS. Polyp distribution, histology and cumulative counts as well as extra-colonic tumours in the pedigree were reviewed.

RESULTS

Twenty-one patients (9 males, 12 females) met study criteria. The median lifetime polyp count was 3 (range 1–36). FHS 8 (80%) was significantly associated with an increased risk of colorectal cancer compared with those with scores <8 who are more likely to develop polyps (P < 0.01). Twelve patients (57%) had predominantly left-sided polyps. Ten colorectal cancers (7 left-sided, 3 right-sided) were diagnosed at a median age of 48 (range 30–74) years. Only three tumours were mucinous or demonstrated tumour-infiltrating lymphocytes, typical of high microsatellite instability tumours. All patients had family history of colorectal cancers (CRCs) and at least 10 patients had a family history of uterine or breast cancer. One patient was found to have hyperplastic polyposis syndrome.

CONCLUSIONS

FCC type X likely represents a heterogenous group of as yet undefined CRC predispositions. The polyp burden and cancer risk are variable and can be somewhat delineated according to an FHS.

High-resolution melting analyses for gene scanning of APC, MLH1, MSH2, and MSH6 associated with hereditary colorectal cancer

BACKGROUND

Hereditary colorectal cancer accounts for approximately 4-5% of all colorectal cancers. The causative genes for familial adenomatous polyposis and hereditary nonpolyposis colorectal cancer are large, making comprehensive analyses difficult. Therefore, high-throughput and practical methods are required to make an early diagnosis of hereditary colorectal cancers and identify high-risk individuals. For this purpose, we developed a novel gene scanning method by high-resolution melting (HRM) analysis.

METHODS

High-resolution melting (HRM) analysis is a promising prescreening method for nucleic acid sequence variants because of its high sensitivity and high-throughput capability. We evaluated HRM for screening APC, MLH1, MSH2, and MSH6 genes for point mutations, small deletions, and insertions. Simultaneously, we evaluated quantitative polymerase chain reaction-HRM (qPCR-HRM) for screening the MSH2 gene for large rearrangements.

RESULTS

All 28 point mutations and 1 large rearrangement were successfully detected by qPCR-HRM analysis.

CONCLUSIONS

A fast and reliable mutation detection strategy with HRM and qPCR-HRM was used to diagnose hereditary colorectal cancers. Because this method is simple and economical, it may be useful in diagnostic laboratories.

Microsatellite instability among individuals of Hispanic origin with colorectal cancer

BACKGROUND

Although the presence of microsatellite instability (MSI) in patients with colorectal cancer (CRC) may have implications for prognosis, therapy, and family counseling, to the authors' knowledge, the prevalence of MSI has not been well described among individuals of Hispanic origin with CRC residing in the United States.

METHODS

A retrospective cohort study using a hospital-based tumor registry to identify individuals of Hispanic origin who were diagnosed with CRC was conducted. Clinical data and tumor samples were retrieved. Molecular analyses included testing for MSI using a panel of 5 mononucleotide markers (BAT25, BAT26, NR21, NR24, and NR27) in a pentaplex polymerase chain reaction assay, as well as immunohistochemistry for the mismatch repair (MMR) proteins mutL homolog (MLH) 1, mutS homolog (MSH) 2, MSH6, and postmeiotic segregation increased 2 (PMS2) 2 on representative tissue.

RESULTS

A total of 111 individuals of Hispanic origin with CRC were identified. Approximately 41.4% were women, and the median age was 57 years (interquartile range [IQR], 47.1-63.5 years). Eleven patients (9.9%; 95% confidence interval [95% CI], 4.2%-15.6%) had MSI CRC, whereas 14 patients (12.6%; 95% CI, 7.3%-21.8%) had CRC with ≥1 MMR protein abnormality. Ten of 11 individuals with MSI had clinical or molecular characteristics suspicious for Lynch syndrome such as abnormal expression of MSH2 and/or MSH6 (n=7) or age<50 years at the time of diagnosis (n=7).

CONCLUSIONS

The prevalence of MSI CRC among Hispanic individuals may be similar to that of other races and ethnicities, but clinicopathological characteristics, including age at diagnosis and pattern of abnormal MMR protein expression, suggest that sporadic MSI CRC may be less common in individuals of Hispanic origin, and that much of the MSI observed in this situation may be attributable to Lynch syndrome. Further exploration of the causes of disparate presentations of CRC by ethnicity and race is warranted.

Evaluating Lynch syndrome in very early onset colorectal cancer probands without apparent polyposis

To characterize the frequency of germline mutations associated with Lynch syndrome and review the potential expanded differential diagnoses in very early onset colorectal cancer (CRC) cases without apparent polyposis. Retrospectively reviewed medical records of 96 probands with CRC diagnosed prior to age 36 from three cancer centers. Determined the frequency of germline mutations in probands meeting different clinical criteria used to identify Lynch syndrome. Three of 46 (6.5%) single case indicators (probands without additional personal or family history suspicious for Lynch syndrome) were identified to carry a deleterious or suspected deleterious mismatch repair (MMR) mutation compared with 10 of 19 (52.6%) in the cases meeting at least one additional revised Bethesda guideline, and 11 of 15 (73.3%) in the cases meeting Amsterdam criteria. Two families without MMR mutations were documented to have a germline APC or TP53 mutation after additional clinical features were identified. Our results suggest that single cases of CRC (those without additional personal or family history suspicious of Lynch syndrome) diagnosed prior to age 36 infrequently have identifiable MMR mutations, especially when compared to cases meeting additional criteria. Careful attention to evolving or additional clinical features is warranted and may lead to an alternate genetic diagnosis in families with early onset CRC.

Phenotypic and genotypic heterogeneity in the Lynch syndrome: diagnostic, surveillance and management implications

Lynch syndrome is the most common form of hereditary colorectal cancer (CRC). This review covers the cardinal features of Lynch syndrome with particular emphasis upon its diagnostic criteria, molecular genetics, natural history, genetic counseling, surveillance and management. Considerable attention has been given to the etiologic role of mismatch repair (MMR) genes as well as low penetrance alleles and modifier genes. The American founder mutation, a deletion of exons 1-6 of MSH2, is discussed in some detail, owing to its high frequency in the US (19 000-30 000 carriers). Genetic counseling is essential prior to patients' undergoing DNA testing and again when receiving their test results. Families with a lower incidence of CRC and extracolonic cancers, in the face of being positive for Amsterdam I criteria but who do not have MMR deficiency by tumor testing, are probably not Lynch syndrome, and thereby should preferably be designated as familial CRC of undetermined type. Patients who are either noncompliant or poorly compliant with colonoscopy, and who are MMR mutation positive, may be candidates for prophylactic colectomy, while MMR mutation-positive women who are noncompliant with gynecologic surveillance may be candidates for prophylactic hysterectomy and bilateral salpingo-oophorectomy.

Denaturing high performance liquid chromatography for the detection of microsatellite instability using bethesda and pentaplex marker panels

Microsatellite instability (MSI) is a characteristic molecular phenotype of tumors from the hereditary nonpolyposis colorectal cancer (Lynch) syndrome. Routine MSI screening of tumors in younger patients is an efficient prescreening tool for the population-based detection of Lynch syndrome in the absence of family cancer history. We describe here the optimization of a denaturing high performance liquid chromatography (DHPLC) assay for MSI analysis with the "Bethesda" panel of markers recommended by the National Cancer Institute and with a more recently proposed "pentaplex" panel of 5 mononucleotide repeat markers. By using various polymerase chain reaction primers and tumor DNA samples with known MSI status, each of the 3 standard DHPLC formats tested could correctly identify the MSI status without the "stutter peaks" inherent in the capillary electrophoresis (CE) methods that are currently in use. Dilution experiments showed that the detection limit for MSI using DHPLC was at least 1:100, thus avoiding the need for tumor enrichment by microdissection before analysis. Concordance between CE and DHPLC for the detection of instability in the Bethesda panel markers was 95%. Optimal DHPLC running conditions for the pentaplex mononucleotide panel are also described. In conclusion, DHPLC provides a sensitive and specific alternative for routine MSI analysis that is free of the stutter peaks observed with CE and which can be used with either the Bethesda or pentaplex mononucleotide marker panels.

Managing hereditary gastrointestinal cancer syndromes: the partnership between genetic counselors and gastroenterologists

A standard of care for the recognition and management of patients and families with hereditary gastrointestinal cancer syndromes is emerging, and both gastroenterologists and genetic counselors have an important role. This Review considers these roles and outlines the partnership needed between gastroenterologists and genetic counselors. The role of the gastroenterologist involves careful sampling of polyps and tumors, and requires a basic working knowledge of the features of hereditary gastrointestinal cancer syndromes. The role of the genetic counselor is to gather and synthesize family history and pathology information, formulate a genetic differential diagnosis, determine a genetic testing strategy, guide medical management and help patients communicate information to their relatives. Managing the complex logistics of testing the best candidate in the family, facilitating informed consent, outlining costs to patients and interpreting test results are also responsibilities assumed by genetic counselors. In addition, genetic counselors help physicians meet their ethical and medicolegal obligations with respect to patient management and family communication. Referral schemata for patients with polyposis and nonpolyposis features are presented in this Review, along with comprehensive tables that outline the features of well-known and rare syndromes that heighten the risk of gastrointestinal malignancy.

Clinical features and mismatch repair genes analyses of Chinese suspected hereditary non-polyposis colorectal cancer: a cost-effective screening strategy proposal

China has the largest numbers of hereditary non-polyposis colorectal cancer (HNPCC) patients based on its population of 1.4 billion. However, the clinical data and mismatch repair (MMR) gene analyses have been limited. Here we performed microsatellite instability (MSI) and immunohistochemistry (IHC) analyses on a series of patients with a high-risk for HNPCC: 61 patients with family histories fulfilling Amsterdam criteria II (ACII-HNPCC) or suspected HNPCC criteria (S-HNPCC), and 106 early onset colorectal cancer (CRC) patients. Sixty late-onset CRC patients were used as control. Methylation of the hMLH1 promoter was analyzed on tumors lacking hMLH1 expression. MMR germ-line mutations were screened on patients with tumors classified as MSI-H/L or negative for IHC. We identified 27 germ-line MMR variants in the 167 patients with a high-risk for HNPCC while only one germ-line mutation in hMSH6 was found in the late-onset CRC group. Of those, 23 were pathogenic mutations. The high incidence of gastric and hepatobiliary cancers coupled with the increasing number of small families in China reduces the sensitivity (43.5%, 30.4%) and positive predictive value (PPV) (45.5%, 17.9%) of the ACII- or S-HNPCC criteria. MSI or IHC testing are highly sensitive in detecting pathogenic mutations (sensitivities = 91.3% and 95.6%, respectively), but the PPVs are quite low (25.6% and 27.8%, respectively). Considering that all 12 tumors with pathogenic mutations in hMLH1 also showed promoter unmethylation, the sensitivity of IHC in conjunction with hMLH1 promoter methylation analysis is not reduced, but the PPV was increased from 27.8% to 61.1%, and the total cost was greatly reduced.

Câncer ano-reto-cólico: aspectos atuais II - câncer colorretal - fatores de riscos e prevenção

O câncer colorretal é curável e passível de prevenção. A chave para o alcance desses objetivos é relativamente simples e pode ser aplicada em escala populacional. Basta, para tanto, que sejamos capazes de conscientizar os médicos, independente da sua área especial de atuação, e proporcionar às pessoas o mais fácil alcance às informações médicas expressas em termos simples sobre a profilaxia e o diagnóstico precoce dessa neoplasia maligna, sobretudo, destacando os fatores protetores e os de riscos, principalmente os que são suscetíveis de ser modificados.

Germline hMSH2 promoter mutation in a Chinese HNPCC kindred: evidence for dual role of LOH

Hereditary non-polyposis colorectal cancer (HNPCC) is a dominantly inherited cancer predisposition syndrome that is caused by germline mutations in mismatch repair genes. By screening the core promoters of hMSH2, hMLH1, and hMSH6 in 37 Chinese suspected HNPCC families, a novel germline mutation c.-78_-79delGT was found in the hMSH2 promoter. Its pathogenic effects were supported by the following findings: (a) it co-segregated with HNPCC-related cancers and was not present in the 220 control subjects, (b) tumors harboring the mutation lacked the expression of hMSH2 and showed high microsatellite instability, (c) it significantly decreased the promoter activity, and (d) it abolished the binding ability of the transcription factor E1A-F. Loss of heterozygosity (LOH) was found in three of the tumors studied. Intriguingly, in the tumors from patients II:1 and III:1, LOH occurred in the wild-type allele and agreed well with the traditional 'two-hit' model. In contrast, in the tumor from patient III:3, LOH occurred in the mutant allele. A pathogenic somatic mutation (c.2210+1G>A) was also found in this tumor; therefore, we proposed that the 'second hit' was inactivated by somatic mutation, and the mutant allele was lost during tumor progression; this provided evidence for the new hypothesis for the dual role of LOH.

Cost-effectiveness of surveillance programs for families at high and moderate risk of hereditary non-polyposis colorectal cancer

OBJECTIVES

Surveillance programs are recommended to both families at high risk (Amsterdam-positive families with known- and unknown mutation) and moderate risk (families not fulfilling all Amsterdam criteria) of colorectal cancer (CRC). Cost-effectiveness has so far only been estimated for the group at high risk. The aim of the present study is to determine cost-effectiveness of surveillance programs where families at both high and moderate risk of HNPCC participate.

METHODS

A decision analytic model (Markov model) is developed to assess surveillance programs where families at high and moderate risk of HNPCC are offered surveillance from age 25 and age 45, respectively. The model includes costs for all families referred to genetic counseling, including genetic risk assessment, mutation analysis, and surveillance in relevant families with or without known mutation, plus the costs related to any surgical treatment. The risk of metachronous CRC is also modeled.

RESULTS

Incremental costs per life year gained are estimated to be euro 980 when families at both high and moderate risk of HNPCC undergo surveillance (euro 508 for high risk and euro 1600 for moderate risk) and euro 1947 when the moderate risk group is evaluated genetically but not offered surveillance. Sensitivity analysis showed these findings to be robust, although cost-effectiveness can be improved in cases of more conservative referrals to genetic counseling.

CONCLUSIONS

The result for high risk families confirms the findings in similar studies. Somewhat surprisingly, cost-effectiveness improves when surveillance of the moderate risk groups are included in the decision model.

Waiver of individual patient consent in research: when do potential benefits to the community outweigh private rights?

Health services research is important to ensure continued best quality of care, but often uses data obtained without explicit consent for this purpose. Obtaining consent may be difficult for many reasons, but excluding individuals may introduce biases that alter the significance of studies. Approval by ethics committees of a waiver of the need for consent allowed our study to proceed and provide evidence that has led to the implementation of a population-based screening policy for the prospective detection of hereditary non-polyposis colorectal cancer. This screening policy has resulted in more cases being detected routinely with better management for affected patients and their at-risk families. A need for consent would have prohibited this study, and the development of a more efficient screening policy could have been delayed for several more years. Ethics committees can effectively manage the need to uphold basic ethical principles without unnecessarily impeding socially useful research. Committees need to be familiar with the guidelines approved under sections 95 and 95A of the Privacy Act 1988 (Cwlth) in addition to the National Health and Medical Research Council National statement on ethical conduct in research involving humans.

Very low prevalence of germline MSH6 mutations in hereditary non-polyposis colorectal cancer suspected patients with colorectal cancer without microsatellite instability

Hereditary non-polyposis colorectal cancer (HNPCC) is caused by mutations in one of the mismatch repair genes MLH1, MSH2, MSH6, or PMS2 and results in high-level microsatellite instability (MSI-high) in tumours of HNPCC patients. The MSI test is considered reliable for indicating mutations in MLH1 and MSH2, but is questioned for MSH6. Germline mutation analysis was performed in 19 patients with an MSI-high tumour and absence of MSH2 and/or MSH6 protein as determined by immunohistochemistry (IHC), without an MLH1 or MSH2 mutation, and in 76 out of 295 patients suspected of HNPCC, with a non-MSI-high colorectal cancer (CRC). All 295 non-MSI-high CRCs were analysed for presence of MSH6 protein by IHC. In 10 patients with an MSI-high tumour without MSH2 and/or MSH6 expression, a pathogenic MSH6 mutation was detected, whereas no pathogenic MSH6 mutation was detected in 76 patients with a non-MSI-high CRC and normal MSH6 protein expression. In none of the 295 CRCs loss of MSH6 protein expression was detected. The prevalence of a germline MSH6 mutation is very low in HNPCC suspected patients with non-MSI-high CRC. Microsatellite instability analysis in CRCs is highly sensitive to select patients for MSH6 germline mutation analysis.

[Implantation of a hospital registry of hereditary nonpolyposis colorectal cancer]

INTRODUCTION

Identification of patients with hereditary nonpolyposis colorectal cancer (HNPCC) can allow colorectal cancer (CRC) prevention through colonoscopy and polypectomies. The purpose of this study was to report the clinical characteristics of HNPCC families in our registry.

PATIENTS AND METHOD

HNPCC was identified using the Amsterdam criteria. Familial clustering of CRC and extracolonic cancers were investigated in families. Individuals at risk were offered annual colonoscopy, starting from the age of 25 years.

RESULTS

Twelve HNPCC families were identified. There were 46 cases of CRC in 38 patients. The mean age at diagnosis of CRC was 45.4 +/- 12.7 years (range 25-73 years). In patients with documented disease, right-sided tumors predominated. Eleven patients with extracolonic cancer were identified (six tumors located in the endometrium). Of 43 at-risk individuals, 29 accepted surveillance.

CONCLUSIONS

Our data confirm the importance of the family history in identifying HNPCC. This study confirms previously described characteristics in HNPCC, namely, early age at onset of CRC, right-sided predominance, multiple synchronous and metachronous neoplasms, and increased extracolonic cancers. This is the first study of clinical data in a Spanish HNPCC registry.

Identification and survival of carriers of mutations in DNA mismatch-repair genes in colon cancer

BACKGROUND

The identification of mutations in germ-line DNA mismatch-repair genes at the time of diagnosis of colorectal cancer is important in the management of the disease.

METHODS

Without preselection and regardless of family history, we recruited 870 patients under the age of 55 years soon after they received a diagnosis of colorectal cancer. We studied these patients for germ-line mutations in the DNA mismatch-repair genes MLH1, MSH2, and MSH6 and developed a two-stage model by multivariate logistic regression for the prediction of the presence of mutations in these genes. Stage 1 of the model incorporated only clinical variables; stage 2 comprised analysis of the tumor by immunohistochemical staining and tests for microsatellite instability. The model was validated in an independent population of patients. We analyzed 2938 patient-years of follow-up to determine whether genotype influenced survival.

RESULTS

There were 38 mutations among the 870 participants (4 percent): 15 mutations in MLH1, 16 in MSH2, and 7 in MSH6. Carrier frequencies in men (6 percent) and women (3 percent) differed significantly (P<0.04). The addition of immunohistochemical analysis in stage 2 of the model had a sensitivity of 62 percent and a positive predictive value of 80 percent. There were 35 mutations in the validation series of 155 patients (23 percent): 19 mutations in MLH1, 13 in MSH2, and 3 in MSH6. The performance of the model was robust among a wide range of cutoff probabilities and was superior to that of the Bethesda and Amsterdam criteria for hereditary nonpolyposis colorectal cancer. Survival among carriers was not significantly different from that among noncarriers.

CONCLUSIONS

We devised and validated a method of identifying patients with colorectal cancer who are carriers of mutations in DNA repair genes. Survival was similar among carriers and noncarriers.

Microsatellite instability in colorectal cancer

BACKGROUND

Microsatellite instability (MSI) causes hereditary non-polyposis colorectal cancer (HNPCC), and occurs in about 15 per cent of sporadic colorectal cancers. Although the basic mechanisms are not clear, there is increased understanding of the clinicopathological consequences of MSI.

METHODS

Medline was searched for articles with a combination of keywords relating to MSI in colorectal cancer, focusing on molecular mechanisms, clinicopathological implications, and prognostic and predictive value. Emphasis was placed on articles from the past 5 years.

RESULTS

The genetic mechanisms differ in hereditary (germline mutation) and sporadic (epigenetic silencing) colorectal cancer. The MSI pathway frequently has altered transforming growth factor beta receptor II and BAX genes, often beta-catenin, and occasionally p16INK4A and PTEN. Changes in K-ras, adenomatous polyposis coli and p53 are rare. Polymerase chain reaction testing for MSI is superior to immunohistochemistry, but complicated by the number and types of nucleotide markers. The Bethesda panel guides HNPCC testing, but guidelines are lacking for general screening. The presence and role of low-frequency MSI remains controversial. Tumours with MSI tend to occur in the proximal colon and be large, but they have a good prognosis. Their reduced response to adjuvant chemotherapy requires confirmation.

CONCLUSION

Research on colorectal cancer needs to be stratified according to microsatellite status in order further to explore the molecular mechanisms and clinicopathological consequences of MSI.