HNPCC associated with germline mutation in the TGF-beta type II receptor gene

TGF-β signaling in health, disease, and therapeutics

Transforming growth factor (TGF)-β is a multifunctional cytokine expressed by almost every tissue and cell type. The signal transduction of TGF-β can stimulate diverse cellular responses and is particularly critical to embryonic development, wound healing, tissue homeostasis, and immune homeostasis in health. The dysfunction of TGF-β can play key roles in many diseases, and numerous targeted therapies have been developed to rectify its pathogenic activity. In the past decades, a large number of studies on TGF-β signaling have been carried out, covering a broad spectrum of topics in health, disease, and therapeutics. Thus, a comprehensive overview of TGF-β signaling is required for a general picture of the studies in this field. In this review, we retrace the research history of TGF-β and introduce the molecular mechanisms regarding its biosynthesis, activation, and signal transduction. We also provide deep insights into the functions of TGF-β signaling in physiological conditions as well as in pathological processes. TGF-β-targeting therapies which have brought fresh hope to the treatment of relevant diseases are highlighted. Through the summary of previous knowledge and recent updates, this review aims to provide a systematic understanding of TGF-β signaling and to attract more attention and interest to this research area.

Susceptibility to Colorectal Cancer Based on HSD17B4 rs721673 and rs721675 Polymorphisms and Alcohol Intake among Taiwan Biobank Participants: A Retrospective Case Control Study Using the Nationwide Claims Data

Colorectal cancer (CRC) is a major public health issue, and there are limited studies on the association between 17β-hydroxysteroid dehydrogenase type 4 (HSD17B4) polymorphism and CRC. We used two national databases from Taiwan to examine whether HSD17B4 rs721673, rs721675, and alcohol intake were independently and interactively correlated with CRC development. We linked the Taiwan Biobank (TWB) participants’ health and lifestyle information and genotypic data from 2012 to 2018 to the National Health Insurance Database (NHIRD) to confirm their medical records. We performed a genome-wide association study (GWAS) using data from 145 new incident CRC cases and matched 1316 healthy, non-CRC individuals. We calculated the odds ratios (OR) and 95% confidence intervals (CI) for CRC based on multiple logistic regression analyses. HSD17B4 rs721673 and rs721675 on chromosome 5 were significantly and positively correlated with CRC (rs721673 A > G, aOR = 2.62, p = 2.90 × 10−8; rs721675 A > T, aOR = 2.61, p = 1.01 × 10−6). Within the high-risk genotypes, significantly higher ORs were observed among the alcohol intake group. Our results demonstrated that the rs721673 and rs721675 risk genotypes of HSD17B4 might increase the risk of CRC development in Taiwanese adults, especially those with alcohol consumption habits.

Cutaneous Squamous Cell Carcinoma in the Age of Immunotherapy

Cutaneous squamous cell carcinoma (cSCC) is the second most prevalent skin cancer globally. Because most cSCC cases are manageable by local excision/radiotherapy and hardly become life-threatening, they are often excluded from cancer registries in most countries. Compared with cutaneous melanoma that originates from the melanin-producing, neural crest-derived epidermal resident, keratinocyte (KC)-derived cancers are influenced by the immune system with regards to their pathogenetic behaviour. Congenital or acquired immunosurveillance impairments compromise tumoricidal activity and raises cSCC incidence rates. Intriguingly, expanded applications of programmed death-1 (PD-1) blockade therapies have revealed cSCC to be one of the most amenable targets, particularly when compared with the mucosal counterparts arisen in the esophagus or the cervix. The clinical observation reminds us that cutaneous tissue has a peculiarly high immunogenicity that can evoke tumoricidal recall responses topically. Here we attempt to redefine cSCC biology and review current knowledge about cSCC from multiple viewpoints that involve epidemiology, clinicopathology, molecular genetics, molecular immunology, and developmental biology. This synthesis not only underscores the primal importance of the immune system, rather than just a mere accumulation of ultraviolet-induced mutations but also reinforces the following hypothesis: PD-1 blockade effectively restores the immunity specially allowed to exist within the fully cornified squamous epithelium, that is, the epidermis.

National recommendations of the French Genetics and Cancer Group - Unicancer on the modalities of multi-genes panel analyses in hereditary predispositions to tumors of the digestive tract

In case of suspected hereditary predisposition to digestive cancers, next-generation sequencing can analyze simultaneously several genes associated with an increased risk of developing these tumors. Thus, "Gastro Intestinal" (GI) gene panels are commonly used in French molecular genetic laboratories. Lack of international recommendations led to disparities in the composition of these panels and in the management of patients. To harmonize practices, the Genetics and Cancer Group (GGC)-Unicancer set up a working group who carried out a review of the literature for 31 genes of interest in this context and established a list of genes for which the estimated risks associated with pathogenic variant seemed sufficiently reliable and high for clinical use. Pancreatic cancer susceptibility genes have been excluded. This expertise defined a panel of 14 genes of confirmed clinical interest and relevant for genetic counseling: APC, BMPR1A, CDH1, EPCAM, MLH1, MSH2, MSH6, MUTYH, PMS2, POLD1, POLE, PTEN, SMAD4 and STK11. The reasons for the exclusion of the others 23 genes have been discussed. The paucity of estimates of the associated tumor risks led to the exclusion of genes, in particular CTNNA1, MSH3 and NTHL1, despite their implication in the molecular pathways involved in the pathophysiology of GI cancers. A regular update of the literature is planned to up-grade this panel of genes in case of new data on candidate genes. Genetic and epidemiological studies and international collaborations are needed to better estimate the risks associated with the pathogenic variants of these genes either selected or not in the current panel.

Patterns of germline and somatic mutations in 16 genes associated with mismatch repair function or containing tandem repeat sequences

BACKGROUND

We assumed that targeted next-generation sequencing (NGS) of mismatch repair-associated genes could improve the detection of driving mutations in colorectal cancers (CRC) with microsatellite instability (MSI) and microsatellite alterations at selected tetranucleotide repeats (EMAST) and clarify the somatic mutation patterns of CRC subtypes.

MATERIAL AND METHODS

DNAs from tumors and white blood cells were obtained from 81 patients with EMAST(+)/MSI-high (MSI-H), 78 patients with EMAST(+)/microsatellite stable (MSS), and 72 patients with EMAST(-)/MSI-H. The germline and somatic mutations were analyzed with a 16-genes NGS panel.

RESULTS

In total, 284 germline mutations were identified in 161 patients. The most common mutations were in EPCAM (24.8%), MSH6 (24.2%), MLH1 (21.7%), and AXIN2 (21.7%). Germline mutations of AXIN2, POLE, POLD1, and TGFBR2 also resulted in EMAST and MSI. EMAST(+)/MSI-H tumors had a significant higher mutation number (205.9 ± 95.2 mut/MB) than tumors that were only EMAST(+) or MSI-H (118.6 ± 64.2 and 106.2 ± 54.5 mut/MB, respectively; both P < .001). In patients with AXIN2 germline mutations, the number of pathological somatic mutations in the tumors was significantly higher than those without AXIN2 germline mutations (176.7 ± 94.2 mut/MB vs 139.6 ± 85.0 mut/MB, P = .002).

CONCLUSION

Next-generation sequencing could enhance the detection of familial CRC. The somatic mutation burden might result from not only the affected genes in germline mutations but also through the dysfunction of downstream effectors. The AXIN2 gene might associate with hypermutation in tumors. Further in vitro experiments to confirm the causal relationship is deserved.

Human Marfan and Marfan-like Syndrome associated mutations lead to altered trafficking of the Type II TGFβ receptor in Caenorhabditis elegans

The transforming growth factor-β (TGFβ) family plays an important role in many developmental processes and when mutated often contributes to various diseases. Marfan syndrome is a genetic disease with an occurrence of approximately 1 in 5,000. The disease is caused by mutations in fibrillin, which lead to an increase in TGFβ ligand activity, resulting in abnormalities of connective tissues which can be life-threatening. Mutations in other components of TGFβ signaling (receptors, Smads, Schnurri) lead to similar diseases with attenuated phenotypes relative to Marfan syndrome. In particular, mutations in TGFβ receptors, most of which are clustered at the C-terminal end, result in Marfan-like (MFS-like) syndromes. Even though it was assumed that many of these receptor mutations would reduce or eliminate signaling, in many cases signaling is active. From our previous studies on receptor trafficking in C. elegans, we noticed that many of these receptor mutations that lead to Marfan-like syndromes overlap with mutations that cause mis-trafficking of the receptor, suggesting a link between Marfan-like syndromes and TGFβ receptor trafficking. To test this hypothesis, we introduced three of these key MFS and MFS-like mutations into the C. elegans TGFβ receptor and asked if receptor trafficking is altered. We find that in every case studied, mutated receptors mislocalize to the apical surface rather than basolateral surface of the polarized intestinal cells. Further, we find that these mutations result in longer animals, a phenotype due to over-stimulation of the nematode TGFβ pathway and, importantly, indicating that function of the receptor is not abrogated in these mutants. Our nematode models of Marfan syndrome suggest that MFS and MFS-like mutations in the type II receptor lead to mis-trafficking of the receptor and possibly provides an explanation for the disease, a phenomenon which might also occur in some cancers that possess the same mutations within the type II receptor (e.g. colon cancer).

Low Incidence of Hereditary Nonpolyposis Colorectal Cancer Syndrome in a Selected Area of the Lombardy Cancer Registry

Aims and background

Epidemiological investigations on the frequency of hereditary nonpolyposis colorectal cancer (HNPCC) syndrome are few and have shown a variable worldwide incidence ranging from 1% to 7% of all colorectal cancers (CRCs). In Italy, relevant differences have been observed: 2.8-3% of all CRCs in northern regions and less than 1% in southern regions. The aim of the present study was to investigate the HNPCC incidence in a selected area of northern Italy belonging to the Lombardy Cancer Registry.

Methods and study design

We analyzed 197 consecutive patients with newly diagnosed CRCs, histologically verified, and resident in two areas of the Lombardy Cancer Registry. For each case, genetic counseling with at least three generations pedigree reconstruction, HNPCC classification according to Amsterdam criteria, molecular analysis for microsatellite instability and immunohistochemistry for hMLH1 and hMSH2 were performed.

Results

A very low frequency (0.5%) of HNPCC fulfilling the Amsterdam criteria was found in comparison to the other Italian areas. Such an incidence seems to be due to actual population differences and reflects a genetic heterogeneity.

Conclusions

The data underline the importance of a precise knowledge of actual HNPCC incidence in different populations in order to optimize effectiveness and efficiency of screening programs for the disease.

Familial Colorectal Cancer Type X

The genetic background is unknown for the 50-60% of the HNPCC families, who fulfill the Amsterdam criteria, but do not have a mutation in an MMR gene, and is referred to as FCCTX. This study reviews the clinical, morphological and molecular characteristics of FCCTX, and discusses the molecular genetic methods used to localize new FCCTX genes, along with an overview of the genes and chromosomal areas that possibly relate to FCCTX. FCCTX is a heterogeneous group, mainly comprising cases caused by single high-penetrance genes, or by multiple low-penetrance genes acting together, and sporadic CRC cases. FCCTX differs in clinical, morphological and molecular genetic characteristics compared to LS, including a later age of onset, distal location of tumours in the colon, lower risk of developing extracolonic tumours and a higher adenoma/carcinoma ratio, which indicates a slower progression to CRC. Certain characteristics are shared with sporadic CRC, e.g. similarities in gene expression and a high degree of CIN+, with significanly increased 20q gain in FCCTX. Other molecular characteristics of FCCTX include longer telomere length and hypomethylation of LINE-1, both being a possible explanation for CIN+. Some genes in FCCTX families (RPS20, BMPR1A, SEMA4A) have been identified by using a combination of linkage analysis and sequencing. Sequencing strategies and subsequent bioinformatics are improving fast. Exome sequencing and whole genome sequencing are currently the most promising tools. Finally, the involvement of CNV’s and regulatory sequences are widely unexplored and would be interesting for further investigation in FCCTX.

Transforming Growth Factor β Superfamily Signaling in Development of Colorectal Cancer

Transforming growth factor (TGF)-β cytokines signal via a complex network of pathways to regulate proliferation, differentiation, adhesion, migration, and other functions in many cell types. A high percentage of colorectal tumors contain mutations that disrupt TGF-β family member signaling. We review how TGF-β family member signaling is altered during development of colorectal cancer, models of study, interaction of pathways, and potential therapeutic strategies.

A Decade of Discovery in the Genetic Understanding of Thoracic Aortic Disease

Aortic aneurysms are responsible for a significant number of all deaths in Western countries. In this review we provide a perspective on the important progress made over the past decade in the understanding of the genetics of this condition, with an emphasis on the more frequent forms of vascular smooth muscle and transforming growth factor β (TGF-β) signalling alterations. For several nonsyndromic and syndromic forms of thoracic aortic disease, a genetic basis has now been identified, with 3 main pathomechanisms that have emerged: perturbation of the TGF-β signalling pathway, disruption of the vascular smooth muscle cell (VSMC) contractile apparatus, and impairment of extracellular matrix synthesis. Because smooth muscle cells and proteins of the extracellular matrix directly regulate TGF-β signalling, this latter pathway emerges as a key component of thoracic aortic disease initiation and progression. These discoveries have revolutionized our understanding of thoracic aortic disease and provided inroads toward gene-specific stratification of treatment. Last, we outline how these genetic findings are translated into novel pharmaceutical approaches for thoracic aortic disease.

Causes and consequences of microsatellite instability in gastric carcinogenesis

Loss of DNA mismatch repair (MMR) function, due to somatic or germline epi/genetic alterations of MMR genes leads to the accumulation of numerous mutations across the genome, creating a molecular phenotype known as microsatellite instability (MSI). In gastric cancer (GC), MSI occurs in about 15% to 30% of the cases. This review summarizes the current knowledge on the molecular mechanisms underlying the acquisition of MSI in GC as well as on the clinic, pathologic and molecular consequences of the MSI phenotype. Additionally, current therapeutic strategies for GC and their applicability in the MSI subset are also discussed.

Novel LOVD databases for hereditary breast cancer and colorectal cancer genes in the Chinese population

The Human Variome Project (HVP) is an international consortium of clinicians, geneticists, and researchers from over 30 countries, aiming to facilitate the establishment and maintenance of standards, systems, and infrastructure for the worldwide collection and sharing of all genetic variations effecting human disease. The HVP-China Node will build new and supplement existing databases of genetic diseases. As the first effort, we have created a novel variant database of BRCA1 and BRCA2, mismatch repair genes (MMR), and APC genes for breast cancer, Lynch syndrome, and familial adenomatous polyposis (FAP), respectively, in the Chinese population using the Leiden Open Variation Database (LOVD) format. We searched PubMed and some Chinese search engines to collect all the variants of these genes in the Chinese population that have already been detected and reported. There are some differences in the gene variants between the Chinese population and that of other ethnicities. The database is available online at http://www.genomed.org/LOVD/. Our database will appear to users who survey other LOVD databases (e.g., by Google search, or by NCBI GeneTests search). Remote submissions are accepted, and the information is updated monthly.

Loss of CSMD1 expression is associated with high tumour grade and poor survival in invasive ductal breast carcinoma

CUB and SUSHI multiple domain protein 1 (CSMD1) is a candidate tumour suppressor gene that maps to chromosome 8p23, a region deleted in many tumour types including 50% of breast cancers. CSMD1 has homologies to proteins implicated in carcinogenesis. We aimed to study the expression pattern of the CSMD1 protein and evaluate its prognostic importance in invasive ductal carcinoma (IDC). An anti-CSMD1 antibody was developed and validated. The expression pattern of CSMD1 in normal breast and IDC samples was investigated by immunohistochemistry in 275 patients. Univariate and multivariate Cox regression analyses were performed. In normal breast duct epithelial cells, luminal, membranous and cytoplasmic CSMD1 staining was identified. Reduced expression of CSMD1 was detected in 79/275 (28.7%) of IDC cases. Low CSMD1 expression was significantly associated with high tumour grade (P = 0.003). CSMD1 expression was associated with overall survival (OS; HR = 0.607, 95%CI: 0.4-0.91, P = 0.018) but not with disease-free survival (DFS; HR = 0.81, 95%CI: 0.46-1.43, P = 0.48). Multivariate analysis showed that CSMD1, together with Nottingham Prognostic Index, was considered an independent predictor of OS (HR = 0.607, 95%CI: 0.4-0.91, P = 0.018) but not DFS (HR = 0.84, 95%CI: 0.46-1.5, P = 0.573). Reduction of CSMD1 expression was significantly associated with high tumour grade and decreased OS. Therefore, our results support the idea that CSMD1 is a tumour suppressor gene and suggest its possible use as a new prognostic biomarker. The membrane expression pattern of CSMD1 suggests that it may be a receptor or co-receptor involved in the process of signal transduction.

Cancer-associated transforming growth factor beta type II receptor gene mutant causes activation of bone morphogenic protein-Smads and invasive phenotype

Transforming growth factor beta (TGFbeta) plays a key role in maintaining tissue homeostasis by inducing cell cycle arrest, differentiation and apoptosis, and ensuring genomic integrity. Furthermore, TGFbeta orchestrates the response to tissue injury and mediates repair by inducing epithelial to mesenchymal transition and by stimulating cell motility and invasiveness. Although loss of the homeostatic activity of TGFbeta occurs early on in tumor development, many advanced cancers have coopted the tissue repair function to enhance their metastatic phenotype. How these two functions of TGFbeta become uncoupled during cancer development remains poorly understood. Here, we show that, in human keratinocytes, TGFbeta induces phosphorylation of Smad2 and Smad3 as well as Smad1 and Smad5 and that both pathways are dependent on the kinase activities of the type I and II TGFbeta receptors (T beta R). Moreover, cancer-associated missense mutations of the T beta RII gene (TGFBR2) are associated with at least two different phenotypes. One type of mutant (TGFBR2(E526Q)) is associated with loss of kinase activity and all signaling functions. In contrast, a second mutant (TGFBR2(R537P)) is associated with high intrinsic kinase activity, loss of Smad2/3 activation, and constitutive activation of Smad1/5. Furthermore, this TGFBR2 mutant endows the carcinoma cells with a highly motile and invasive fibroblastoid phenotype. This activated phenotype is T beta RI (Alk-5) independent and can be reversed by the action of a dual T beta RI and T beta RII kinase inhibitor. Thus, identification of such activated T beta RII receptor mutations in tumors may have direct implications for appropriately targeting these cancers with selective therapeutic agents.

Some aspects of molecular diagnostics in Lynch syndrome

This manuscript is composed of five parts which summarize five publications in succession. Essentially, they are concerned with molecular diagnostics of Lynch syndrome and are based on studies in 238 families. The finding that young age at diagnosis is the key feature in patients with MSH2 and MLH1 mutations (Part 1) has helped to define simple criteria for the preliminary diagnosis of this syndrome. A cheaper method for the detection of mutations has been developed (Part 2) and applied to study the types of mutations and their prevalence in Poland (Part 3) and the Baltic States (Part 4). A specific feature of these mutations, i.e. presence of recurrent mutations in the majority of affected families with mutations, has suggested the feasibility of effective diagnostics with a single test disclosing all of them. An attempt to reveal other causes of familial aggregation of colorectal cancer has ruled out any association with C insertion in the NOD2 gene (Part 5).

Using genetically engineered mouse models of cancer to aid drug development: an industry perspective

Recent developments in the generation and characterization of genetically engineered mouse models of human cancer have resulted in notable improvements in these models as platforms for preclinical target validation and experimental therapeutics. In this review, we enumerate the criteria used to assess the accuracy of various models with respect to human disease and provide some examples of their prognostic and therapeutic utility, focusing on models for cancers that affect the largest populations. Technological advancements that allow greater exploitation of genetically engineered mouse models, such as RNA interference in vivo, are described in the context of target and drug validation. Finally, this review discusses stratagems for, and obstacles to, the application of these models in the drug development process.

Hereditary non-polyposis colorectal cancer: The rise and fall of a confusing term

The term Hereditary Non-Polyposis Colorectal Cancer (HNPCC) is a poor descriptor of the syndrome described by Lynch. Over the last decade, the term has been applied to heterogeneous groups of families meeting limited clinical criteria, for example the Amsterdam criteria. It is now apparent that not all Amsterdam criteria-positive families have the Lynch syndrome. The term HNPCC has also been applied to clinical scenarios in which CRCs with DNA microsatellite instability are diagnosed but in which there is no vertical transmission of an altered DNA mismatch repair (MMR) gene. A term that has multiple, mutually incompatible meanings is highly problematic, particularly when it may influence the management of an individual family. The Lynch syndrome is best understood as a hereditary predisposition to malignancy that is explained by a germline mutation in a DNA MMR gene. The diagnosis does not depend in an absolute sense on any particular family pedigree structure or age of onset of malignancy. Families with a strong family history of colorectal cancer that do not have Lynch syndrome have been grouped as ‘Familial Colorectal Cancer Type-X’. The first step in characterizing these cancer families is to distinguish them from Lynch syndrome. The term HNPCC no longer serves any useful purpose and should be phased out.

TGFBR1andTGFBR2mutations in patients with features of Marfan syndrome and Loeys-Dietz syndrome

Marfan syndrome (MFS) is an autosomal dominant connective tissue disorder characterized by manifestations in the cardiovascular, skeletal, ocular, and other organ systems. MFS type1 (MFS1) is caused by mutations in the gene encoding fibrillin (FBN1). Recently, the transforming growth factor-beta receptor-2 gene, TGFBR2, has been shown to be associated with a second type of this disorder with typically mild or absent ocular involvement (MFS type 2; MFS2). Several point mutations were found in the highly conserved serine/threonine kinase domain of TGFBR2. Mutations in both TGFBR1 and TGFBR2 are associated with Loeys-Dietz aortic aneurysm syndrome (LDS). We searched for TGFBR1 and TGFBR2 mutations in 41 unrelated patients fulfilling the diagnostic criteria of Ghent nosology or with the tentative diagnosis of Marfan syndrome, in whom mutations in the FBN1 coding region were not identified. In TGFBR1, two mutations and two polymorphisms were detected. In TGFBR2, five mutations and six polymorphisms were identified. Reexamination of patients with a TGFBR1 or TGFBR2 mutation revealed extensive clinical overlap between patients with MFS1, MFS2, and LDS.

Two novel and one known mutation of the TGFBR2 gene in Marfan syndrome not associated with FBN1 gene defects

TGF-beta-receptor 2 (TGFBR2) gene defects have been recently associated with Marfan syndrome (MFS) with prominent cardio-skeletal phenotype in patients with negative fibrillin-1 (FBN1) gene screening. Four mutations have been identified to date in five unrelated families. We screened TGFBR2 gene by direct automated sequencing in two adult patients diagnosed with MFS according to Ghent criteria, and in one girl clinically suspected as affected on the basis of a major cardiovascular criterion and skeletal involvement, all proven not to carry mutations in the exon-intron boundaries of FBN1 gene. We identified two novel and one known TGFBR2 gene mutations in the three unrelated probands. The D446N was identified in a 4-year-old girl with de novo disease characterized by severe cardiovascular disease and skeletal involvement. The M425V and R460H mutations were identified in two familial, autosomal dominant MFSs, both characterized by major cardio-skeletal signs and absence of major ocular signs. The mutation R460H has been recently reported in a family with thoracic aortic aneurysms and dissection. The three mutations are absent in 192 controls and affect evolutionarily conserved residues of the serine/threonine kinase domain (exon 5). Our data support the recently reported association between TGFBR2 gene and MFS without major ocular signs (MFS2). The number of genotyped cases however is too low to confirm that major ocular signs are characteristically absent in MFS2. Accordingly, all patients proven or suspected to be affected by MFS with negative FBN1 gene screening could benefit from rapid investigation of the TGFBR2 gene.

Lynch syndrome (hereditary non-polyposis colorectal cancer): current concepts and approaches to management

Colorectal cancer is among the most frequent causes of cancer death worldwide. An inherited predisposition to cancer of the colon and other organs, Lynch syndrome-- also called hereditary non-polyposis colorectal cancer--is probably the most frequent cause of hereditary cancer and is often found in a colon cancer patient and traced through other family members. However, this syndrome is not only characterized by the early onset of colon cancers but also by a predisposition to a constellation of extraintestinal cancers that tend to be misdiagnosed. With new diagnostic technologies, the incidence of familial/inherited versus sporadic cases may appear to increase, due to the recognition of cancers in families that do not fulfill clinical guidelines developed prior to knowledge of the genetic basis of this disease. We now have the ability and the responsibility to detect and prevent this disease, and equally important, to direct patients to specifically targeted treatment. Specialists should be aware of the significance of inherited colon cancer and should become familiar with the molecular diagnostic tests now widely available.

The genetics of HNPCC: application to diagnosis and screening

Hereditary nonpolyposis colorectal cancer syndrome (HNPCC; Lynch Syndrome) is the most common form of hereditary colorectal cancers. Predisposed individuals have increased lifetime risk of developing colorectal, endometrial and other cancers. The syndrome is primarily due to heterozygous germline mutations in one of the mismatch repair genes; mainly MLH1, MSH2, MSH6 and PMS2. The resulting mismatch repair deficiency leads to microsatellite instability which is the hallmark of tumors arising within this syndrome, as well as a variable proportion of sporadic tumors. Diagnostic guidelines and criteria for molecular testing of suspected families have been proposed and are continuously updated. However, not all families fulfilling these criteria show mutations in mismatch repair genes and/or microsatellite instability implicating other, as yet unknown, carcinogenic mechanisms and predisposition genes. This subset of tumors is the focus of current clinical and molecular research. This review addresses recent advances in the field of HNPCC research and their applications in the management of affected individuals and families.

Surveillance colonoscopy in individuals at risk for hereditary nonpolyposis colorectal cancer: an evidence-based review

PURPOSE

Surveillance colonoscopy plays an important role in the management of asymptomatic patients known to carry and suspected of carrying hereditary nonpolyposis colorectal cancer gene mutations. Although the shortest interval between surveillance examinations may seem to offer the most benefit to patients, excessive use of this procedure may have unwanted consequences. This study was designed to evaluate the evidence and make recommendations regarding the optimal frequency of surveillance colonoscopy and the age at which to initiate surveillance based on the best available evidence.

METHODS

MEDLINE was searched for all articles assessing surveillance colonoscopy from 1966 to 2004 by using the MESH terms "hereditary nonpolyposis colorectal cancer" and "screening." The evidence was systematically reviewed and a critical appraisal of the evidence was performed.

RESULTS

There are no randomized, controlled, clinical trials examining the frequency of surveillance colonoscopy in hereditary nonpolyposis colorectal cancer. Three cohort studies were identified for review. There is one cohort study of good quality that provides evidence that surveillance colonoscopy every three years in patients with hereditary nonpolyposis colorectal cancer reduces the risk of developing colorectal cancer and the risk of death. The two remaining cohort studies provide poor evidence on which to make a recommendation.

CONCLUSIONS

The best available evidence supports surveillance with complete colonoscopy to the cecum every three years in patients with hereditary nonpolyposis colorectal cancer (B recommendation). There is no evidence to support or refute more frequent screening. Further research is required to examine the potential harms and benefits of more frequent screening. However, given the potential for rapid progression from adenoma to carcinoma and missing lesions at colonoscopy, there is consensus that screening more frequently than every three years is required.

Identification and in silico analyses of novelTGFBR1 andTGFBR2 mutations in Marfan syndrome-related disorders

Very recently, heterozygous mutations in the genes encoding transforming growth factor beta receptors I (TGFBR1) and II (TGFBR2) have been reported in Loeys-Dietz aortic aneurysm syndrome (LDS). In addition, dominant TGFBR2 mutations have been identified in Marfan syndrome type 2 (MFS2) and familial thoracic aortic aneurysms and dissections (TAAD). In the past, mutations of these genes were associated with atherosclerosis and several human cancers. Here, we report a total of nine novel and one known heterozygous sequence variants in the TGFBR1 and TGFBR2 genes in nine of 70 unrelated individuals with MFS-like phenotypes who previously tested negative for mutations in the gene encoding the extracellular matrix protein fibrillin-1 (FBN1). To assess the pathogenic impact of these sequence variants, in silico analyses were performed by the PolyPhen, SIFT, and Fold-X algorithms and by means of a 3D homology model of the TGFBR2 kinase domain. Our results showed that in all but one of the patients the pathogenic effect of at least one sequence variant is highly probable (c.722C > T, c.799A > C, and c.1460G > A in TGFBR1 and c.773T > G, c.1106G > T, c.1159G > A, c.1181G > A, and c.1561T > C in TGFBR2). These deleterious alleles occurred de novo or segregated with the disease in the families, indicating a causative association between the sequence variants and clinical phenotypes. Since TGFBR2 mutations found in patients with MFS-related disorders cannot be distinguished from heterozygous TGFBR2 mutations reported in tumor samples, we emphasize the importance of segregation analysis in affected families. In order to be able to find the mutation that is indeed responsible for a MFS-related phenotype, we also propose that genetic testing for sequence alterations in TGFBR1 and TGFBR2 should be complemented by mutation screening of the FBN1 gene.

Evolution of the nomenclature for the hereditary colorectal cancer syndromes

The hereditary forms of colorectal cancer have been given many names historically as the manifestations have been gradually understood. Lynch syndrome has had several names, most prominently 'Hereditary Nonpolyposis Colorectal Cancer' or HNPCC. Clarification of the genetic basis and full phenotypic expression of this disease mandates a more clinically useful name that clarifies the consideration of non-colonic cancers in a family history, and unifies the diagnosis around the germline mutation in a DNA mismatch repair (MMR) gene. The term 'Lynch syndrome' is proposed for the autosomal dominant disease caused by a germline mutation in a DNA MMR gene.

TGFBR1*6A may contribute to hereditary colorectal cancer

PURPOSE

TGFBR16A is a tumor susceptibility gene that increases breast, colon, and ovarian cancer risk. Fourteen percent of the general population carries TGFBR16A, and TGFBR16A homozygotes have a greater than 100% increased colon cancer risk compared with noncarriers. Low-penetrance genes such as TGFBR16A may account for a sizable proportion of familial colorectal cancer occurrences. To test this hypothesis, we determined whether TGFBR16A contributes to a proportion of mismatch repair (MMR) gene mutation-negative hereditary nonpolyposis colorectal cancer (HNPCC) patients.

PATIENTS AND METHODS

A case-case study was performed of 208 index patients with HNPCC meeting the Amsterdam criteria. Patients were examined for mutations and genomic rearrangements in the MLH1, MSH2, and MSH6 genes and genotyped for TGFBR16A. Tumor microsatellite instability status was available for 95 patients.

RESULTS

A total of 144 patients (69.2%) carried a deleterious mutation and were classified as positive for MMR gene mutation; 64 patients (30.8%) had no evidence of mutations and were classified as MMR negative. TGFBR16A allelic frequency was significantly higher among MMR-negative patients (0.195) than among MMR-positive patients (0.104; P = .011). The proportion of TGFBR16A homozygotes was nine-fold higher among MMR-negative (6.3%) than among MMR-positive patients (0.7%; P = .032). The highest TGFBR16A allelic frequency was found among MMR-negative patients with tumors exhibiting no microsatellite instability (0.211), and the lowest frequency was found among MMR-positive patients with tumors exhibiting microsatellite instability (0.121); the difference was not statistically significant (P = .17).

CONCLUSION

TGFBR16A may be causally responsible for a proportion of HNPCC occurrences.

Correlations between phenotype and microsatellite instability in HNPCC: implications for genetic testing

Hereditary nonpolyposis colorectal cancer (HNPCC) is widely considered to be a syndrome of defective mismatch repair (MMR). A major concern with genetic diagnosis of HNPCC is the variable, often low, percentage of pathogenic germline mutations that can be detected in MMR genes using common screening methods. The variable percentage of mutation detected is in part related to the sensitivity of conventional screening methods and may also depend on the heterogeneous genetics of HNPCC. Thus, identification of phenotypic criteria predictive of germline mutations in MMR genes may be helpful in efficient HNPCC genetic testing. Clinical diagnostic criteria, initially developed for HNPCC (e.g., Amsterdam I and II, or Bethesda criteria), can be used to clinically select patient candidates that carry germline mutations in MMR genes. More useful criteria were previously developed by analyzing families with germline MMR mutations. Using a complementary approach based on tumor microsatellite instability analysis, we confirm that the Amsterdam criteria are significantly better than the Bethesda criteria in predicting families with MSI-H tumors (P = 0.0227). Our results also suggest that a cutoff at < 50 years' mean age at diagnosis of HNPCC-related cancers (especially colorectal and endometrial cancer) may be an additional tool for the identification of families with defective MMR. Recent advances in MMR mutation screening are expected to improve detection of pathogenic MMR mutations in these families. Conversely, the high proportion of MSS tumors observed in our series of families with advanced age at cancer diagnosis is consistent with the low percentage of MMR mutations detected by previous studies in families with this phenotype. These families probably carry mutations in other genes that may or may not be related to MMR. Additional studies are necessary to clarify the molecular basis for HNPCC in families with MSS tumors.

Genetic predisposition to colorectal cancer

High-penetrance mutations in several genes have been identified that contribute to hereditary colorectal cancer. The role of these mutations in cancer pathogenesis is well understood and their detection is successfully used in clinical diagnosis. In stark contrast, our understanding of the influence of low-penetrance mutations that account for most of the remaining familial cases of colorectal cancer, as well as an unknown proportion of sporadic cases, is far less advanced. Extensive ongoing research into low-penetrance, multifactorial predisposition to colorectal cancer is now beginning to bear fruit, with important implications for understanding disease aetiology and developing new diagnostic, preventive and therapeutic strategies.

Heterozygous TGFBR2 mutations in Marfan syndrome

Marfan syndrome is an extracellular matrix disorder with cardinal manifestations in the eye, skeleton and cardiovascular systems associated with defects in the gene encoding fibrillin (FBN1) at 15q21.1 (ref. 1). A second type of the disorder (Marfan syndrome type 2; OMIM 154705) is associated with a second locus, MFS2, at 3p25-p24.2 in a large French family (family MS1). Identification of a 3p24.1 chromosomal breakpoint disrupting the gene encoding TGF-beta receptor 2 (TGFBR2) in a Japanese individual with Marfan syndrome led us to consider TGFBR2 as the gene underlying association with Marfan syndrome at the MSF2 locus. The mutation 1524G-->A in TGFBR2 (causing the synonymous amino acid substitution Q508Q) resulted in abnormal splicing and segregated with MFS2 in family MS1. We identified three other missense mutations in four unrelated probands, which led to loss of function of TGF-beta signaling activity on extracellular matrix formation. These results show that heterozygous mutations in TGFBR2, a putative tumor-suppressor gene implicated in several malignancies, are also associated with inherited connective-tissue disorders.

Hereditary nonpolyposis colorectal cancer and related conditions

Hereditary nonpolyposis colorectal cancer (HNPCC) is a cancer-predisposing condition caused by inactivating mutations in at least four genes (MSH2, MLH1, MSH6, and PMS2) belonging to the mismatch repair system. At present, availability of the microsatellite instability (MSI) test allows screening of a relevant fraction of patients with a constellation of features suggestive of HNPCC. By analogy with several other genetic disorders, it is clearly emerging that the term HNPCC encompasses a wide spectrum of different clinical presentations, including Muir-Torre syndrome, Turcot syndrome, and the neurofibromatosis-hematological malignancy association. Notwithstanding the remarkable genetic and allelic heterogeneity, a few consistent phenotype-genotype associations can be recognized. Mutations in the MSH2 gene entail higher risks of developing cancer, including extraintestinal ones, than MLH1 alterations. MSH2 also accounts for most cases of Muir-Torre syndrome, which is characterized by the presence of sebaceous skin tumors. The few known PMS2 mutations show a striking association with the presence of gliomas, which are the hallmark of the Turcot variant of HNPCC. Homozygotes for mismatch repair gene mutations present with stigmata of neurofibromatosis 1 and usually die in childhood due to a variety of leukemias and lymphomas. While such correlations are being defined, the underlying reasons have only partially been elucidated, and may include heterogeneous gene functions and properties; types of mutation, some of which may exert dominant negative effects; and genetic and environmental modifiers.

Genetic predisposition as a basis for chemoprevention, surgical and other interventions in colorectal cancer

Strategies of cancer prevention are generally developed with the population at large in mind. However, special attention is warranted for those persons with rare genetic traits associated with a greatly elevated risk of developing colorectal cancer (CRC) and some other malignancies: Orphan diseases demand Orphan preventive measures! Recent advances in modern genetics have enhanced our understanding of several genes and the specific germ-line mutations responsible for colorectal carcinogenesis. A number of features provide evidence for a genetic predisposition to CRC. These include typical clinical and histological features of a particular syndrome, a familial aggregation of CRC and associated malignancies, young age at onset of CRC, occurrence of multiple neoplasias and/or unusual localisation of the tumour (e.g., right side of the colon). In hereditary colorectal cancer, genetic testing can easily be demonstrated as cost-effective.

Nuclear Pedigree Criteria of Suspected HNPCC

The criteria for the diagnosis of HNPCC established by the ICG-HNPCC are very restrictive as they do not allow for the diagnosis of a large number of "suspected HNPCC" cases - these are families which do no fulfill the strict diagnostic "Amsterdam criteria", but do present with several pedigree and clinical features characteristic for HNPCC. Several series of families suspected of harboring germline mutations in DNA mismatch repair genes have been studied for germline changes in DNA mismatch repair genes and a mutation rate of somewhere between 8-60% was found. Therefore a subgroup of members of the ICG-HNPCC has been working on pedigree/clinical diagnostic criteria for suspected HNPCC.

Materials and methods

Results

The combination of features - i.e. the occurrence of an HNPCC associated cancer (CRC or cancer of the endometrium, small bowel or urinary tract) in a 1st degree relative of a CRC patient; at least one of the patients being diagnosed under age of 50 - appeared to be strongly associated to HNPCC with an OR - 161. Constitutional mutations were identified in 18 (10 MLH1 and 8 MSH2 mutations) of 52 (34%) cases matching the above features.

Conclusions

The results of our studies strongly suggest that it is possible to diagnose HNPCC with a high degree of accuracy on the basis of nuclear pedigree data and clinical features.

Genomics in colorectal cancer: godsend or gimmick?

Genomics and the new techniques it embraces, such as cDNA and tissue arrays, comparative genomic hybridization and single nucleotide polymorphism analysis, offer the opportunity to generate massive amounts of data relating to screening, aetiology, diagnosis, prognostication and optimal treatment in colorectal cancer. To make progress, studies must be designed to stringently test these new technologies and compare them to the tried and tested gold standards. This is best done in the form of large randomized controlled trials. Genomics undoubtedly offers the prospect of exciting new developments in the field of colorectal cancer but these should be regarded with caution until they are proved superior to present practices and models.

TGFBR1*6A and cancer risk: a meta-analysis of seven case-control studies

PURPOSE

TGFBR1*6A is a hypomorphic polymorphic allele of the type I transforming growth factor beta receptor (TGFBR1). TGFBR1*6A is a candidate tumor susceptibility allele that has been associated with an increased incidence of various types of cancer. This study was undertaken to analyze all published case-control studies on TGFBR1*6A and cancer and determine whether TGFBR1*6A is associated with cancer.

PATIENTS AND METHODS

All published case-control studies assessing the germline frequency of TGFBR1*6A were included. Studies assessing TGFBR1*6A in tumors were excluded. The results of seven studies comprising 2,438 cases and 1,846 controls were pooled and analyzed.

RESULTS

Overall, TGFBR1*6A carriers have a 26% increased risk of cancer (odds ratio [OR], 1.26; 95% confidence interval [CI], 1.07 to 1.49). Cancer risk for TGFBR1*6A homozygotes (OR, 2.53; 95% CI, 1.39 to 4.61) is twice that of TGFBR1*6A heterozygotes (OR, 1.26; 95% CI, 1.04 to 1.51). Analysis of various types of tumors shows that TGFBR1*6A carriers are at increased risk of developing breast cancer (OR, 1.48; 95% CI, 1.11 to 1.96), hematological malignancies (OR, 1.70; 95% CI, 1.13 to 2.54), and ovarian cancer (OR, 1.53; 95% CI, 1.07 to 2.17). Carriers of TGFBR1*6A who are from the United States are at increased risk of colorectal cancer (OR, 1.38; 95% CI, 1.02 to 1.86). However, Southern European TGFBR1*6A carriers have no increased colorectal cancer risk. There is no association between TGFBR1*6A and bladder cancer.

CONCLUSION

TGFBR1*6A is emerging as a highfrequency, low-penetrance tumor susceptibility allele that predisposes to the development of breast, ovarian, and colorectal cancer, as well as hematologic malignancies.

Genetic studies of pulmonary arterial hypertension

These genetic studies of primary pulmonary hypertension (PPH) initially tried to define immunogenetic subsets. Because only small subsets could be classified when defined by HLA/autoantibody associations and the familial form of PPH failed to segregate with the HLA class II locus, the focus shifted to a genome scan of families with PPH (FPPH). This approach identified a gene on chromosome 2q33,34 called PPH1. Mutations in this gene, now known to be bone morphogenetic protein receptor 2 (BMPR2), can cause PPH. Mutations in a second gene, ALK-1, present in families with hereditary hemorrhagic telangiectasia type 2, also causes PPH. Both genes, involved in TGF-B signaling, provide exciting clues for defining the pathogenesis of PPH.

Loss of Smad signaling in human colorectal cancer is associated with advanced disease and poor prognosis

PURPOSE

Based largely on in vitro investigations and animal studies, investigators believe that disruptions of transforming growth factor-beta (TGF-beta) signaling contribute to the development and progression of human colorectal cancer. The purpose of this study was to directly assess the status of the TGF-beta signaling pathway in colorectal cancer and determine the effects of its disruption on clinical behavior and outcome.

MATERIALS AND METHODS

Smad proteins are the principal intracellular components of the TGF-beta signaling pathway. We conducted a high-throughput analysis of the expression patterns of Smad2, phosphorylated (activated) Smad2 (pSmad2), and Smad4 in more than 600 human colorectal cancer specimens assembled in tissue microarrays.

RESULTS

The vast majority (93.8%; 95% CI: 92%-96%) of colorectal cancers expressed phosphorylated Smad2, indicating the ability of the tumors to survive and proliferate within a microenvironment that contains bioactive TGF-beta. Twelve of 633 (1.9%; 95% CI: 1%-3%) cases failed to express Smad2, and 15 of 641 (2.3%; 95% CI: 1%-4%) cases failed to express Smad4. Moreover, 29 of 615 (4.7%; 95% CI: 3%-7%) of cases expressed Smad2 but not its activated form (pSmad2), suggesting the presence of a TGF-beta receptor defect. Based on an analysis of 577 cases for which clinical outcome information was available, failure to express Smad2, pSmad2, or Smad4 was associated with advanced-stage disease, the presence of lymph node metastases, and a significantly shorter overall survival (median survival: 35 vs 58 months).

DISCUSSION

Loss of Smad activation and/or expression occurs in approximately 10% of colorectal cancers. This subset has a poor prognosis because of its association with advanced disease and the presence of lymph node metastases at diagnosis.

Genetic and epigenetic alterations in colon cancer

Colorectal cancer affected approximately 135,000 people in the United States in 2001, resulting in 57,000 deaths. Colorectal cancer develops as the result of the progressive accumulation of genetic and epigenetic alterations that lead to the transformation of normal colonic epithelium to colon adenocarcinoma. The loss of genomic stability is a key molecular and pathophysiologic step in this process and serves to create a permissive environment for the occurrence of alterations in tumor suppressor genes and oncogenes. Alterations in these genes, which include APC, CTNNB1, K-RAS, MADH4/SMAD4, and TGFBR2, appear to promote colon tumorigenesis by perturbing the function of signaling pathways, such as the TGF-ss signaling pathway, or by affecting genes that regulate genomic stability, such as the mutation mismatch repair genes.

Pathogenesis and clinical management of hereditary non-polyposis colorectal cancer

BACKGROUND

Hereditary non-polyposis colorectal cancer (HNPCC) is an inherited genetic condition associated with microsatellite instability; it accounts for around 5 per cent of all cases of colorectal cancer. This review examines recent data on management strategies for this condition.

METHODS

A Medline-based literature search was performed using the keywords 'HNPCC' and 'microsatellite instability'. Additional original papers were obtained from citations in articles identified by the initial search.

RESULTS AND CONCLUSION

The Amsterdam criteria identify patients in whom the presence of an inherited mutation should be investigated. Those with a mutation should be offered counselling and screening. The role of prophylactic surgery has been superseded by regular colonoscopy, which dramatically reduces the risk of colorectal cancer. Screening for extracolonic malignancy is also advocated, but the benefits are uncertain. Chemoprevention may be of value in lowering the incidence of bowel cancer in affected patients, but further studies are required.

hMLH1 and hMSH2 gene mutation in Brazilian families with suspected hereditary nonpolyposis colorectal cancer

BACKGROUND

The aim of this study was to search for mutations in the human mutS homolog 2 (hMSH2) and human mutL homolog 1 (hMLH1) genes in 25 unrelated Brazilian kindreds with suspected hereditary nonpolyposis colorectal cancer (HNPCC).

METHODS

The families were grouped according to the following clinical criteria: Amsterdam I or II; familial colorectal cancer (CRC); an early age of onset of CRC in the proband only; or with at least one or two relatives who had HNPCC-related cancers; CRC in the proband only. All patients were studied with direct sequencing.

RESULTS

Ten mutations were detected (10 of 25 [40%]); of nine different mutations, seven were novel. The hMLH1 gene had a higher mutation detection rate than hMSH2 (8 of 25 [32%] vs. 2 of 25 [8%]). Only 3 of these 10 families fulfilled the Amsterdam criteria. Two different polymorphisms were detected in the hMLH1 gene and four in the hMSH2 gene.

CONCLUSIONS

The hMLH1 gene had a higher mutation detection rate than hMSH2. The physician who deals with CRC must take into consideration the heredity issue with patients who present with an early age of onset or a familial history of CRC- or HNPCC-related cancers, including gastric cancer, even if they do not fulfill the former Amsterdam criteria.

Cellular and molecular mechanisms of carcinogenesis

Our understanding of the cellular and molecular mechanisms of cancer of the gastrointestinal tract has increased dramatically over the last several decades. We are identifying new players in the pathways toward cancer with increasing frequency. In addition, we have come to understand that no single pathway acts by itself; in vivo, the effects are combinatorial. As new and better cell culture and animal models of carcinogenesis arise, our knowledge will continue to grow. As we learn more, we will be able to translate the results of our research into new and better techniques for the diagnosis and treatment of gastrointestinal cancers.

Pathology--a molecular prognostic approach

Colorectal cancer affects 29,000 people and kills approximately 15,000 in England and Wales each year, most of these deaths resulting from the effects of local or distant recurrence. There is a need to give these patients accurate prognoses and individualised treatment regimens. At present, the best prognostic markers are clinicopathological. Post-genomic science and the new high throughput technologies offer unrivalled opportunities to understand the biology and molecular pathology of colorectal cancer. These technologies should be used in the context of large randomised controlled trials to identify new molecular prognostic and predictive markers and also new targets for therapy.

DNA mismatch repair defects: role in colorectal carcinogenesis

The inactivation of the DNA mismah repair (MMR) system, which is associated with the predisposition to the hereditary non-polyposis colorectal cancer (HNPCC), has also been documented in nearly 20% of the sporadic colorectal cancers. These tumors are characterized by a high frequency of microsatellite instability (MSI(+) phenotype), resulting from the accumulation of small insertions or deletions that frequently arise during replication of these short repeated sequences. A germline mutation of one of the two major MMR genes (hMSH2 or hMLH1) is found in half to two-thirds of the patients with HNPCC, whereas in sporadic cases hypermethylation of the hMLH1 promoter is the major cause of the MMR defect. Germline mutations in hMSH6 are rare and rather confer predisposition to late-onset familial colorectal cancer, and frequent extracolonic tumors. Yet, the genetic background of a number of HNPCC patients remains unexplained, indicating that other genes participate in MMR and play important roles in cancer susceptibility. The tumor-suppressor genes that are potential targets for the MSI-driven mutations because they contain hypermutable repeated sequences are likely to contribute to the etiology and tissue specificity of the MSI-associated carcinogenesis. Because the prognosis and the chemosensitivity of the MSI(+) colorectal tumors differ from those without instability, the determination of the MSI phenotype is expected to improve the clinical management of patients. This review gives an overview of various aspects of the biochemistry and genetics of the DNA mismah repair system, with particular emphasis in its role in colorectal carcinogenesis.

Mutation frequency in coding and non-coding repeat sequences in mismatch repair deficient cells derived from normal human tissue

Repetitive tracts within the coding regions of TGFBR2 and BAX are frequently mutated in mismatch repair deficient tumours and are implicated in tumour progression. However, there has been little study of the balance between selection pressure and inherent instability at sequences within these genes. To determine whether TGFBR2 and BAX are inherently prone to mutations in the presence of MMR defects, we studied MMR deficient cells derived from B-lymphocytes. By analysing cells derived from normal tissue we aimed to minimize the effects of selection pressures that bias the apparent frequency of mutation. We definitively show that certain sequences, usually repaired by MMR, are inherently unstable. Using a small pool PCR technique we confirmed these cells exhibit microsatellite instability. Additionally, we demonstrate that MMR deficiency results in an excess of mutations, specifically at the poly(A)(10) tract compared to other regions of the TGFBR2 gene (P<0.001). Conversely, an excess of mutations does not appear to arise at the poly(G)(8) tract of the BAX gene. These studies provide insight into the mechanism by which TGFBR2 and BAX genes become mutated during tumorigenesis. These findings invoke the notion of "unmasking" specific hypermutable sequences in particular genes adding further complexity to the concept of the mutator phenotype.

Evaluation of Bethesda guidelines in relation to microsatellite instability

PURPOSE

The Bethesda guidelines were developed for selection of patients whose tumors should be tested for high microsatellite instability. This study examined the validity of the different Bethesda criteria in relation to microsatellite instability status to simplify their use in clinical practice.

METHODS

A total of 164 patients with colorectal or hereditary nonpolyposis colorectal cancer-associated cancers were registered on the basis of the Amsterdam criteria without age limitations (11 cases), multiple tumors (2 cases), the accumulation of colorectal cancer in the family (no first-degree relatives affected or the index patient's age up to 50 years; 45 cases), an early age at onset up to 50 years (13 cases), morphologic and histopathologic manifestations (right-sided colorectal cancer, mucinous undifferentiated histology; 1 case), and the Bethesda criteria (92 cases). The microsatellite instability status of tumors was determined using the International Collaborative Group on Hereditary Non-Polyposis Colorectal Cancer marker reference panel.

RESULTS

When applying all Bethesda criteria, high microsatellite instability tumors were identified in our hereditary nonpolyposis colorectal cancer registry with a sensitivity of 87 percent. Twenty-nine percent (27/92) of the Bethesda-positive patients displayed high microsatellite instability compared with 6 percent of patients (4/72) not meeting these criteria (P < 0.001). Only Bethesda Criteria 1, 3, and 4 showed a significantly different distribution of the microsatellite instability status when compared with those of the remaining patients registered (P < or = 0.001). These three criteria detected high microsatellite instability tumors in 48 percent (10/21), 50 percent (18/36), and 31 percent (21/67) of patients, respectively. When applying these criteria only, a cumulative detection rate of 77 percent of all (24/31) high microsatellite instability cases was found, thereby identifying 89 percent of high microsatellite instability tumors among the Bethesda-positive patients. Patients matching Criteria 1, 3, and 4 frequently showed hMSH2 or hMLH1 germline mutations and tumor-specific loss of protein expression.

CONCLUSION

In our hereditary nonpolyposis colorectal cancer registry the complete Bethesda criteria showed the highest sensitivity to identify patients with high microsatellite instability tumors. However, for general medical practice outside academic centers, three criteria are reasonably accurate for adequate high microsatellite instability tumor selection.