Immunohistochemistry identifies carriers of mismatch repair gene defects causing hereditary nonpolyposis colorectal cancer

Lynch syndrome and Muir-Torre phenotype associated with a recurrent variant in the 3'UTR of the MSH6 gene

A MSH6 3'UTR variant (c.*23_26dup) was found in 13 unrelated families consulted for Lynch/Muir-Torre Syndrome. This variant, which is very rare in the genomic databases, was absent in healthy controls and strongly segregated with the disease in the studied pedigrees. All tumors were defective for MSH2/MSH6/MSH3 proteins expression, but only MSH2 somatic pathogenic mutations were found in 5 of the 12 sequenced tumors. Moreover, we had no evidence of MSH6 transcript decrease in carriers, whereas MSH2 transcript was downregulated. Additional evaluations performed in representative carriers, including karyotype, arrayCGH and Linked-Reads whole genome sequencing, failed to evidence any MSH2 germline pathogenic variant. Posterior probability of pathogenicity for MSH6 c.*23_26dup was obtained from a multifactorial analysis incorporating segregation and phenotypic data and resulted >0.999, allowing to classify the variant as pathogenic (InSiGHT Class 5). Carriers shared a common haplotype involving MSH2/MSH6 loci, then a cryptic disease-associated variant, linked with MSH6 c.*23_26dup, cannot be completely excluded. Even if it is not clear whether the MSH6 variant is pathogenic per se or simply a marker of a disease-associated MSH2/MSH6 haplotype, all data collected on patients and pedigrees prompted us to manage the variant as pathogenic and to offer predictive testing within these families.

Screening for Lynch Syndrome by Immunohistochemistry of Mismatch Repair Proteins: Significance of Indeterminate Result and Correlation With Mutational Studies

CONTEXT.—

Immunohistochemical expression of mismatch repair (MMR) protein is a well-accepted method for routine screening for Lynch syndrome with relatively high sensitivity and specificity. Occasionally, however, immunohistochemistry (IHC) can yield an equivocal result with poor reproducibility and the potential for misdiagnosis.

OBJECTIVE.—

To determine the frequency and significance of indeterminate MMR IHC expression in patients routinely screened for Lynch syndrome and correlation with germline mutation studies.

DESIGN.—

Semiquantitative scoring of MMR IHC was performed by image analysis in 479 cases, of which 380 were colorectal and 99 endometrial cancer. Scores of 10% or more, less than 10%, and 0% were used as cutoffs for retained, indeterminate, and loss of expression, respectively. Negative and indeterminate IHC results were confirmed by mutational studies.

RESULTS.—

Four hundred eighteen of 479 cases (87.2%) were reported as retained expression, 45 (9.3%) as loss of expression, and 16 (3.3%) as indeterminate expression. Fifteen of 45 (33.3%) and 8 of 16 (50%) with loss and indeterminate expression, respectively, were found to have Lynch syndrome by germline studies. The overall frequency of Lynch syndrome in our patient population was 4.8% (23 of 479), and 34.7% of these (8 of 23) were associated with indeterminate IHC expression. In the indeterminate group, MLH1 germline mutation was the most frequent (6 of 13; 46.2%), followed by MSH6 (4 of 13; 30.7%).

CONCLUSIONS.—

Our findings provide further evidence that indeterminate IHC should be further investigated for possible MMR germline mutation. Guidelines for interpretation of MMR IHC and the establishment of more objective criteria for defining indeterminate results are important to improve the sensitivity and specificity of the IHC assay.

A systematic review and economic evaluation of diagnostic strategies for Lynch syndrome

BACKGROUND

Lynch syndrome (LS) is an inherited autosomal dominant disorder characterised by an increased risk of colorectal cancer (CRC) and other cancers, and caused by mutations in the deoxyribonucleic acid (DNA) mismatch repair genes.

OBJECTIVE

To evaluate the accuracy and cost-effectiveness of strategies to identify LS in newly diagnosed early-onset CRC patients (aged < 50 years). Cascade testing of relatives is employed in all strategies for individuals in whom LS is identified.

DATA SOURCES AND METHODS

Systematic reviews were conducted of the test accuracy of microsatellite instability (MSI) testing or immunohistochemistry (IHC) in individuals with CRC at risk of LS, and of economic evidence relating to diagnostic strategies for LS. Reviews were carried out in April 2012 (test accuracy); and in February 2012, repeated in February 2013 (economic evaluations). Databases searched included MEDLINE (1946 to April week 3, 2012), EMBASE (1980 to week 17, 2012) and Web of Science (inception to 30 April 2012), and risk of bias for test accuracy was assessed using the Quality Assessment of Diagnostic Accuracy Studies-2 (QUADAS-2) quality appraisal tool. A de novo economic model of diagnostic strategies for LS was developed.

RESULTS

Inconsistencies in study designs precluded pooling of diagnostic test accuracy results from a previous systematic review and nine subsequent primary studies. These were of mixed quality, with significant methodological concerns identified for most. IHC and MSI can both play a part in diagnosing LS but neither is gold standard. No UK studies evaluated the cost-effectiveness of diagnosing and managing LS, although studies from other countries generally found some strategies to be cost-effective compared with no testing. The de novo model demonstrated that all strategies were cost-effective compared with no testing at a threshold of £20,000 per quality-adjusted life-year (QALY), with the most cost-effective strategy utilising MSI and BRAF testing [incremental cost-effectiveness ratio (ICER) = £5491 per QALY]. The maximum health benefit to the population of interest would be obtained using universal germline testing, but this would not be a cost-effective use of NHS resources compared with the next best strategy. When the age limit was raised from 50 to 60 and 70 years, the ICERs compared with no testing increased but remained below £20,000 per QALY (except for universal germline testing with an age limit of 70 years). The total net health benefit increased with the age limit as more individuals with LS were identified. Uncertainty was evaluated through univariate sensitivity analyses, which suggested that the parameters substantially affecting cost-effectiveness: were the risk of CRC for individuals with LS; the average number of relatives identified per index patient; the effectiveness of colonoscopy in preventing metachronous CRC; the cost of colonoscopy; the duration of the psychological impact of genetic testing on health-related quality of life (HRQoL); and the impact of prophylactic hysterectomy and bilateral salpingo-oophorectomy on HRQoL (this had the potential to make all testing strategies more expensive and less effective than no testing).

LIMITATIONS

The absence of high-quality data for the impact of prophylactic gynaecological surgery and the psychological impact of genetic testing on HRQoL is an acknowledged limitation.

CONCLUSIONS

Results suggest that reflex testing for LS in newly diagnosed CRC patients aged < 50 years is cost-effective. Such testing may also be cost-effective in newly diagnosed CRC patients aged < 60 or < 70 years. Results are subject to uncertainty due to a number of parameters, for some of which good estimates were not identified. We recommend future research to estimate the cost-effectiveness of testing for LS in individuals with newly diagnosed endometrial or ovarian cancer, and the inclusion of aspirin chemoprevention. Further research is required to accurately estimate the impact of interventions on HRQoL.

STUDY REGISTRATION

This study is registered as PROSPERO CRD42012002436.

FUNDING

The National Institute for Health Research Health Technology Assessment programme.

Outcomes of screening endometrial cancer patients for Lynch syndrome by patient-administered checklist

OBJECTIVE

The aims of this study were to implement a patient-administered checklist designed to identify endometrial cancer patients at elevated risk for Lynch syndrome; measure subsequent genetic counseling and testing; and identify differences between those who attended genetic counseling and those who did not.

METHODS

We developed a 4-item yes/no checklist of personal and family history risk factors for Lynch syndrome-associated endometrial cancer and recommended referral for genetic counseling for patients meeting any of the criteria. Retrospective chart review was performed to determine subsequent genetic counseling and testing outcomes over a 15 month period.

RESULTS

6/387 (1.6%) of endometrial cancer patients tested positive for a Lynch syndrome mutation. 4/24 (17%) of endometrial cancer patients who met referral criteria and attended genetic counseling tested positive. 38/70 (55%) of patients who met referral criteria were not seen for genetic counseling. Patients who were diagnosed with endometrial cancer at younger ages, who had primary surgery at our institution, or who met more than one referral criteria were more likely to be seen for genetic counseling.

CONCLUSIONS

Endometrial cancer patients who met referral criteria and attended genetic counseling comprised a population enriched for Lynch syndrome. This approach allowed Lynch syndrome evaluation resources to be targeted to a population of patients that is high risk and interested in the information. The referral rate of at-risk patients needs to be improved, and allocating resources towards this goal could increase the identification of Lynch syndrome while avoiding some of the pitfalls of universal screening.

Germline mutation analysis of MLH1 and MSH2 in Malaysian Lynch syndrome patients

AIM: To investigate the protein expression profile of mismatch repair (MMR) genes in suspected cases of Lynch syndrome and to characterize the associated germline mutations.

METHODS: Immunohistochemical analysis of tumor samples was performed to determine the protein expression profile of MMR protein. Germline mutation screening was carried out on peripheral blood samples. The entire exon regions of MLH1 and MSH2 genes were amplified by polymerase chain reaction, screened by denaturing high performance liquid chromatography (dHPLC) and analyzed by DNA sequencing to characterize the germline mutations.

RESULTS: Three out of 34 tissue samples (8.8%) and four out of 34 tissue samples (11.8%) showed loss of nuclear staining by immunohistochemistry, indicating the absence of MLH1 and MSH2 protein expression in carcinoma cells, respectively. dHPLC analysis followed by DNA sequencing showed these samples to have germline mutations of MSH2 gene. However, no deleterious mutations were identified in any of the 19 exons or coding regions of MLH1 gene, but we were able to identify MLH1 promoter polymorphism, -93G > A (rs1800734), in 21 out of 34 patients (61.8%). We identified one novel mutation, transversion mutation c.2005G > C, which resulted in a missense mutation (Gly669Arg), a transversion mutation in exon 1, c.142G > T, which resulted in a nonsense mutation (Glu48Stop) and splice-site mutation, c.2006-6T > C, which was adjacent to exon 13 of MSH2 gene.

CONCLUSION: Germline mutations were identified in four Malaysian Lynch syndrome patients. Immunohistochemical analysis of tumor tissue proved to be a good pre-screening test before proceeding to germline mutation analysis of DNA MMR genes.

A comparative study of quantitative immunohistochemistry and quantum dot immunohistochemistry for mutation carrier identification in Lynch syndrome

Aims

Lynch Syndrome is caused by mutations in DNA mismatch repair (MMR) genes. Mutation carrier identification is facilitated by immunohistochemical detection of the MMR proteins MHL1 and MSH2 in tumour tissue and is desirable as colonoscopic screening reduces mortality. However, protein detection by conventional immunohistochemistry (IHC) is subjective, and quantitative techniques are required. Quantum dots (QDs) are novel fluorescent labels that enable quantitative multiplex staining. This study compared their use with quantitative 3,3′-diaminobenzidine (DAB) IHC for the diagnosis of Lynch Syndrome.

Methods

Tumour sections from 36 mutation carriers and six controls were obtained. These were stained with DAB on an automated platform using antibodies against MLH1 and MSH2. Multiplex QD immunofluorescent staining of the sections was performed using antibodies against MLH1, MSH2 and smooth muscle actin (SMA). Multispectral analysis of the slides was performed. The staining intensity of DAB and QDs was measured in multiple colonic crypts, and the mean intensity scores calculated. Receiver operating characteristic (ROC) curves of staining performance for the identification of mutation carriers were evaluated.

Results

For quantitative DAB IHC, the area under the MLH1 ROC curve was 0.872 (95% CI 0.763 to 0.981), and the area under the MSH2 ROC curve was 0.832 (95% CI 0.704 to 0.960). For quantitative QD IHC, the area under the MLH1 ROC curve was 0.812 (95% CI 0.681 to 0.943), and the area under the MSH2 ROC curve was 0.598 (95% CI 0.418 to 0.777).

Conclusions

Despite the advantage of QD staining to enable several markers to be measured simultaneously, it is of lower utility than DAB IHC for the identification of MMR mutation carriers. Automated DAB IHC staining and quantitative slide analysis may enable high-throughput IHC.

Selection of patients with germline MLH1 mutated Lynch syndrome by determination of MLH1 methylation and BRAF mutation

Lynch syndrome is one of the most common hereditary colorectal cancer (CRC) syndrome and is caused by germline mutations of MLH1, MSH2 and more rarely MSH6, PMS2, MLH3 genes. Whereas the absence of MSH2 protein is predictive of Lynch syndrome, it is not the case for the absence of MLH1 protein. The purpose of this study was to develop a sensitive and cost effective algorithm to select Lynch syndrome cases among patients with MLH1 immunohistochemical silencing. Eleven sporadic CRC and 16 Lynch syndrome cases with MLH1 protein abnormalities were selected. The BRAF c.1799T> A mutation (p.Val600Glu) was analyzed by direct sequencing after PCR amplification of exon 15. Methylation of MLH1 promoter was determined by Methylation-Sensitive Single-Strand Conformation Analysis. In patients with Lynch syndrome, there was no BRAF mutation and only one case showed MLH1 methylation (6%). In sporadic CRC, all cases were MLH1 methylated (100%) and 8 out of 11 cases carried the above BRAF mutation (73%) whereas only 3 cases were BRAF wild type (27%). We propose the following algorithm: (1) no further molecular analysis should be performed for CRC exhibiting MLH1 methylation and BRAF mutation, and these cases should be considered as sporadic CRC; (2) CRC with unmethylated MLH1 and negative for BRAF mutation should be considered as Lynch syndrome; and (3) only a small fraction of CRC with MLH1 promoter methylation but negative for BRAF mutation should be true Lynch syndrome patients. These potentially Lynch syndrome patients should be offered genetic counselling before searching for MLH1 gene mutations.

Semiquantitative assessment of immunohistochemistry for mismatch repair proteins in Lynch syndrome

AIMS

To assess semiquantitative immunohistochemistry as used in the diagnosis of Lynch syndrome.

METHODS AND RESULTS

Tumour sections from 51 mutation carriers and 17 controls were stained with antibodies against MLH1, MSH2, MSH6 and PMS2. Intensity of immunoreactivity and percentage positivity were recorded on scales of 0-3 and 0-4, respectively. These scores were multiplied for a score of 0-12 per slide. Receiver-operator characteristic (ROC) curves of staining performance for the identification of mutation carriers were evaluated, and optimum cut-offs calculated. The area under the MLH1 ROC curve was 0.981 [95% confidence interval (CI) 0.952, 1.000]. The area under the MSH2 ROC curve was 0.899 (95% CI 0.796, 1.000). For MLH1 staining, a score<or=4 gives a sensitivity of 100.0% (95% CI 84.0, 100.0) and a specificity of 91.5% (95% CI 79.6, 97.6) for identifying MLH1 mutation carriers. For MSH2 staining, a score<or=4 gives a sensitivity of 87.5% (95% CI 61.7, 98.4) and specificity of 88.5% (95% CI 76.5, 95.6) for identifying MSH2 mutation carriers.

CONCLUSIONS

This study supports a semiquantitative slide assessment method. Protein expression may occur in the context of known pathogenic mutations, a potential pitfall in the screening process.

Current clinical criteria for Lynch syndrome are not sensitive enough to identify MSH6 mutation carriers

Background

Reported prevalence, penetrance and expression of deleterious mutations in the mismatch repair (MMR) genes, MLH1, MSH2, MSH6 and PMS2, may reflect differences in the clinical criteria used to select families for DNA testing. The authors have previously reported that clinical criteria are not sensitive enough to identify MMR mutation carriers among incident colorectal cancer cases.

Objective

To describe the sensitivity of the criteria when applied to families with a demonstrated MMR mutation.

Methods

Families with an aggregation of colorectal cancers were examined for deleterious MMR mutations according to the Mallorca guidelines. All families with a detected MMR mutation as of November 2009 were reclassified according to the Amsterdam and Bethesda criteria.

Results

Sixty-nine different DNA variants were identified in a total of 129 families. The original Amsterdam clinical criteria were met by 38%, 12%, 78% and 25% of families with mutations in MSH2, MSH6, MLH1 and PMS2, respectively. Corresponding numbers for the revised Amsterdam criteria were 62%, 48%, 87% and 38%. Similarly, each of the four clinical Bethesda criteria had low sensitivity for identifying MSH6 or PMS2 mutations.

Conclusion

Amsterdam criteria and each of the Bethesda criteria were inadequate for identifying MSH6 mutation-carrying kindreds. MSH6 mutations may be more common than currently assumed, and the penetrance/expression of MSH6 mutations, as derived from families meeting current clinical criteria, may be misleading. To increase detection rate of MMR mutation carriers, all cancers in the Lynch syndrome tumour spectrum should be subjected to immunohistochemical analysis and/or analysis for microsatellite instability.

Germ-line mutations in mismatch repair genes associated with prostate cancer

Genetic predisposition to prostate cancer includes multiple common variants with a low penetrance (single nucleotide polymorphisms) and rare variants with higher penetrance. The mismatch repair (MMR) genes MLH1, MSH2, MSH6, and PMS2 are associated with Lynch syndrome where colon and endometrial cancers are the predominant phenotypes. The purpose of our study was to investigate whether germ-line mutations in these genes may be associated with prostate cancer. One hundred and six male carriers or obligate carriers of MMR mutations were identified. Nine had contracted prostate cancer. Immunohistochemical analysis was done on tumor tissue from eight of the nine tumors. Observed incidence, cumulative risk at 60 and 70 years of age, age of onset, and Gleason score were compared with expected as assessed from population-based series. Absence of gene product from the mutated MMR gene was found in seven of eight tumors. Expected number of prostate cancers was 1.52 compared with 9 observed (P < 0.01). Mean age of onset of prostate cancer was 60.4 years compared with 66.6 expected (P = 0.006); the number of men with a Gleason score between 8 and 10 was significantly higher than expected (P < 0.00001). Kaplan-Meier analysis suggested that cumulative risk by 70 years in MMR mutation carriers may be 30% (SE, 0.088) compared with 8.0% in the general population. This is similar to the high risk associated with BRCA2 mutations. To our knowledge, this study is the first to indicate that the MMR genes may be among the rare genetic variants that confer a high risk of prostate cancer when mutated.

PMS2 involvement in patients suspected of Lynch syndrome

It is well-established that germline mutations in the mismatch repair genes MLH1, MSH2, and MSH6 cause Lynch syndrome. However, mutations in these three genes do not account for all Lynch syndrome (suspected) families. Recently, it was shown that germline mutations in another mismatch repair gene, PMS2, play a far more important role in Lynch syndrome than initially thought. To explore this further, we determined the prevalence of pathogenic germline PMS2 mutations in a series of Lynch syndrome-suspected patients. Ninety-seven patients who had early-onset microsatellite instable colorectal or endometrial cancer, or multiple Lynch syndrome-associated tumors and/or were from an Amsterdam Criteria II-positive family were selected for this study. These patients carried no pathogenic germline mutation in MLH1, MSH2, or MSH6. When available, tumors were investigated for immunohistochemical staining (IHC) for PMS2. PMS2 was screened in all patients by exon-by-exon sequencing. We identified four patients with a pathogenic PMS2 mutation (4%) among the 97 patients we selected. IHC of PMS2 was informative in one of the mutation carriers, and in this case, the tumor showed loss of PMS2 expression. In conclusion, our study confirms the finding of previous studies that PMS2 is more frequently involved in Lynch syndrome than originally expected.

High risk for ovarian cancer in a prospective series is restricted to BRCA1/2 mutation carriers

PURPOSE

Inherited ovarian cancer carries a serious prognosis. Prophylactic oophorectomy has been advocated. The degree to which inherited ovarian cancer is restricted to BRCA mutation carriers is not fully known. We wanted to determine the prevalence of BRCA mutation carriers in women at high risk from ovarian cancer.

EXPERIMENTAL DESIGN

Healthy women who were found to be at increased risk judged by family history were followed prospectively. Full BRCA1/2 mutation analysis was conducted on all patients who contracted pelvic cancer.

RESULTS

We identified 1,582 women at risk during 5,674 person-years. Forty infiltrating epithelial ovarian cancers, six peritoneal cancers, and one fallopian tube cancer were diagnosed. All but one of these patients (98%) had a BRCA mutation, a frequency that was significantly higher than for the 3 patients with borderline ovarian cancers, who were all mutation negative (P = 0.0002). Eighty-two percent of the detected mutations belonged to one of the 10 Norwegian founder mutations previously reported. At prophylactic bilateral salpingo-oophorectomy, cancer was found in 18 of 345 (5.2%) of mutation carriers compared with none in the 446 mutation negative (P = 0.0000).

CONCLUSIONS

In healthy women with a family history of ovarian cancer, high risk for ovarian cancer was restricted to BRCA1/2 mutation carriers. A woman at risk for ovarian cancer according to her family history should have access to full BRCA1/2 mutation testing before deciding on prophylactic bilateral salpingo-oophorectomy.

Tumor characteristics as an analytic tool for classifying genetic variants of uncertain clinical significance

It is important to identify a germline mutation in a patient with an inherited cancer syndrome to allow mutation carriers to be included in cancer surveillance programs, which have been proven to save lives. Many of the mutations identified result in premature termination of translation, and thus in loss-of-function of the encoded mutated protein. However, the significance of a large proportion of the sequence changes reported is unknown. Some of these variants will be associated with a high risk of cancer and have direct clinical consequence. Many criteria can be used to classify variants with unknown significance; most criteria are based on the characteristics of the amino acid change, on segregation data and appearance of the variant, on the presence of the variant in controls, or on functional assays. In inherited cancers, tumor characteristics can also be used to classify variants. It is worthwhile to examine the clinical, morphological and molecular features of a patient, and his or her family, when assessing whether the role of a variant is likely to be neutral or pathogenic. Here we describe the advantages and disadvantages of using the tumor characteristics of patients carrying germline variants of uncertain significance (VUS) in BRCA1, BRCA2, or in one of the mismatch repair (MMR) genes, MLH1, MSH2, or MSH6, to infer pathogenicity.

Multiplex SNaPshot genotyping for detecting loss of heterozygosity in the mismatch-repair genes MLH1 and MSH2 in microsatellite-unstable tumors

BACKGROUND

In the workup of patients with suspected hereditary nonpolyposis colorectal cancer (HNPCC), detection of loss of heterozygosity (LOH) could help pinpoint the mismatch-repair (MMR) gene carrying the germline mutation, but analysis of microsatellite markers has proved unreliable for this purpose. We developed a simple, low-cost method based on single-nucleotide polymorphism (SNP) genotyping and capillary electrophoresis for the assessment of LOH at 2 MMR loci simultaneously.

METHODS

We used the Applied Biosystems SNaPshot Multiplex Kit with meticulously selected primers to assess 14 common SNPs in MLH1 [mutL homolog 1, colon cancer, nonpolyposis type 2 (E. coli)] and MSH2 [mutS homolog 2, colon cancer, nonpolyposis type 1 (E. coli)] and optimized the protocol for DNA isolated from peripheral blood and fresh/frozen or archival microsatellite-unstable tumors from patients with confirmed (n = 42) or suspected (n = 25) HNPCC. The 42 tumors from patients with confirmed MLH1 or MSH2 germline mutations were used to validate the method's diagnostic accuracy against results obtained with DNA sequencing or multiplex ligation-dependent probe amplification.

RESULTS

The SNaPshot assay provided better detection of certain SNPs than DNA sequencing. The MLH1 and MSH2 SNP marker sets were informative in 82% and 76% of the 67 cases analyzed, respectively. The new assay displayed 100% specificity for detecting LOH and predicted the location of the germline mutation in 40% of the cases (54% of those involving MLH1, 22% in MSH2).

CONCLUSIONS

Our SNP-based method for detecting LOH in MLH1 and MSH2 is simple to perform with instruments available in most clinical genetics laboratories. It can be a valuable addition to protocols now used to guide mutational screening of patients with suspected HNPCC.

Hereditary nonpolyposis colorectal cancer (Lynch syndrome): molecular pathogenesis and clinical approaches to diagnosis and management for nurses

Hereditary nonpolyposis colorectal cancer (HNPCC), also referred to as Lynch syndrome, is the most common form of hereditary colorectal cancer and is responsible for 2% to 4% of all colorectal cancers in the Western hemisphere. Generally characterized by early-onset colorectal carcinoma with a mean age of presentation of 40 to 45 years, it can also manifest with extracolonic adenocarcinomas and cancers of the endometrium, ovaries, stomach, pancreas, small intestine, hepatobiliary tract, upper uroepithelial tract, brain, and skin. HNPCC is autosomal dominant and carries an 80% lifetime risk of cancer development. This review addresses the molecular underpinnings of HNPCC while providing a concise approach to clinical detection, diagnosis, and management of patients who may or may not test positive for an HNPCC-causing mutation. Although applicable to any patient-care setting in which cancer may be observed, this review specifically addresses the role of nurses in detecting, diagnosing, and clinically managing HNPCC.

Identification and classification of hereditary nonpolyposis colorectal cancer (Lynch syndrome): adapting old concepts to recent advancements. Report from the Italian Association for the study of Hereditary Colorectal Tumors Consensus Group

Knowledge about hereditary nonpolyposis colorectal cancer (HNPCC)/Lynch syndrome clearly evolved during the last 10 to 15 years much more rapidly than in the past century. Consequently, long-established concepts and attitudes that held for many years should now be changed or updated. With regard to classification, we suggest maintaining the eponym "Lynch syndrome" for families that have a well-documented deficiency of the DNA mismatch repair system, whereas "clinical hereditary nonpolyposis colorectal cancer" should be reserved for those families that meet the Amsterdam criteria but without evidence of mismatch repair impairment. Any family (or individual) meeting one or more of the Bethesda criteria can be considered as suspected HNPCC. For the identification of hereditary colorectal cancer molecular screening or the pedigree analysis show advantages and disadvantages; the ideal would be to combine the two approaches. Diffusion of the microsatellite instability test and of immunohistochemistry in the pathology laboratories might render in the immediate future molecular screening more realistic. Strict endoscopic surveillance of family members at risk (with first colonoscopy at age 20-25 years and then every 2-3 years) is needed only in families with documented alterations of the DNA mismatch repair. To a certain extent, our conclusions were similar to the recently proposed "European guidelines for the clinical management of HNPCC," although we prefer the term "clinical hereditary nonpolyposis colorectal cancer," instead of familial colorectal cancer, for families meeting the Amsterdam criteria but not having evidence of mismatch repair impairment.

Familial breast/ovarian cancer and BRCA1/2 genetic screening: the role of immunohistochemistry as an additional method in the selection of patients

Only 20-25% of families screened for BRCA1/2 mutations are found positive. Because only a positive result is informative, we studied the role of BRCA1/2 immunohistochemistry as an additional method for patient selection. From 53 high-risk-affected probands, 18 (34%) had available paraffin blocks of their tumors and were selected for this study. Mutation screening was done by conformation-sensitive gel electrophoresis and multiplex ligation-dependent probe amplification. For immunohistochemistry, 21 neoplastic specimens (15 breast carcinomas, 5 ovary neoplasms, and 1 rectal adenocarcinoma) were analyzed with BRCA1 (monoclonal antibody, Ab-1, oncogene) and BRCA2 (polyclonal antibody, Ab-2, oncogene) antibodies. Absence of the BRCA1 protein was confirmed in negative tumors by Western blotting. Seven patients were positive for BRCA1/2 mutations: 5 for BRCA1 and 2 for BRCA2. Four out of five positive patients had tumors negative for BRCA1 immunostaining, and the remaining 13 BRCA1-negative patients had positive BRCA1 immunostaining in all tumor samples. Sensitivity to predict for BRCA1 mutation carriers was 80%, and specificity was 100%, with a positive predictive value of 100% and a negative predictive value of 93%. This correlation was statistically significant (p=0.001). No correlation was observed for BRCA2. If larger studies confirm these results, high-risk patients with BRCA1-negative tumors should be screened first for this gene.

Functional analysis of human MLH1 variants using yeast and in vitro mismatch repair assays

The functional characterization of nonsynonymous single nucleotide polymorphisms in human mismatch repair (MMR) genes has been critical to evaluate their pathogenicity for hereditary nonpolyposis colorectal cancer. We previously established an assay for detecting loss-of-function mutations in the MLH1 gene using a dominant mutator effect of human MLH1 expressed in Saccharomyces cerevisiae. The purpose of this study is to extend the functional analyses of nonsynonymous single nucleotide polymorphisms in the MLH1 gene both in quality and in quantity, and integrate the results to evaluate the variants for pathogenic significance. The 101 MLH1 variants, which covered most of the reported MLH1 nonsynonymous single nucleotide polymorphisms and consisted of one 3-bp deletion, 1 nonsense and 99 missense variants, were examined for the dominant mutator effect by three yeast assays and for the ability of the variant to repair a heteroduplex DNA with mismatch bases by in vitro MMR assay. There was diversity in the dominant mutator effects and the in vitro MMR activities among the variants. The majority of functionally inactive variants were located around the putative ATP-binding pocket of the NH(2)-terminal domain or the whole region of the COOH-terminal domain. Integrated functional evaluations contribute to a better prediction of the cancer risk in individuals or families carrying MLH1 variants and provide insights into the function-structure relationships in MLH1.

Risk perception, worry and satisfaction related to genetic counseling for hereditary cancer

In this multi center study, genetic counseling for hereditary cancer was evaluated by assessing patients' worry, perceived risk of developing cancer and satisfaction with genetic counseling. An overall aim was to identify characteristics of vulnerable patients in order to customize genetic counseling. In addition, agreement between patients' and counselors' scores was measured. A total of 275 Norwegian patients were consecutively recruited, and 213 completed questionnaires before and after genetic counseling. Patients' perceived risk decreased after the genetic counseling session. There was incongruence between risk perception expressed as a percentage and in words. Patients were significantly less worried after counseling. Higher levels of worry were predicted by low instrumental satisfaction with counseling, high degree of perceived risk of developing cancer and younger age. In conclusion, counselors met the patients' psychological needs to a satisfactory degree during counseling. However, patients did not fully understand their risk of developing cancer.

Prevention of colorectal cancer by colonoscopic surveillance in families with hereditary colorectal cancer

OBJECTIVE

In recent years persons at risk for colorectal cancers (CRC) have been subjected to follow-up with colonoscopy in many centres. There is, however, limited knowledge about the effect of such interventions. The objective of this study was to report the results of our observations during the past 15 years.

MATERIAL AND METHODS

Healthy persons were included in the study according to their family history of CRCs, and prospectively followed with colonoscopies.

RESULTS

Altogether, 1133 individuals were included and observed for a total of 3474 follow-up years from the first to the last colonoscopy initiated by our activity. Mismatch repair (MMR) mutations were detected in 6.5% of cases. A total of 1383 polyps were removed, 72% were less than 5 mm in diameter. Findings were scored as hyperplastic polyps (n=887), adenomas with mild to moderate dysplasia (n=460), adenomas with high-grade dysplasia (n=30) and cancers (n=6). Two cancers were observed after the first colonoscopy, compared with 2.6 expected by chance and more than 20 expected under the hypothesis of predominant inherited diseases in the families. Observed annual incidence rates for adenomas were similar in all groups, while in the mutation carriers there was a higher frequency of progression to severe dysplasia or infiltrating cancer.

CONCLUSIONS

A simple explanation for the combined findings may be that all selected families had a similar tendency to produce adenomas, while mutation carriers more frequently demonstrated dysplasia/cancer in the adenomas. The low annual incidence rates for CRC indicated that the removal of adenomas may have prevented cancers.

Incorporation of somatic BRAF mutation testing into an algorithm for the investigation of hereditary non-polyposis colorectal cancer

Patients suspected on clinical grounds to have hereditary non-polyposis colorectal cancer (HNPCC) may be offered laboratory testing in order to confirm the diagnosis and to facilitate screening of pre-symptomatic family members. Tumours from an affected family member are usually pre-screened for microsatellite instability (MSI) and/or loss of immunohistochemical expression of mismatch repair (MMR) genes prior to germline MMR gene mutation testing. The efficiency of this triage process is compromised by the more frequent occurrence of sporadic colorectal cancer (CRC) showing high levels of MSI (MSI-H) due to epigenetic loss of MLH1 expression. Somatic BRAF mutations, most frequently V600E, have been described in a significant proportion of sporadic MSI-H CRC but not in HNPCC-associated cancers. BRAF mutation testing has therefore been proposed as a means to more definitively identify and exclude sporadic MSI-H CRC cases from germline MMR gene testing. However, the clinical validity and utility of this approach have not been previously evaluated in a familial cancer clinic setting. Testing for the V600E mutation was performed on MSI-H CRC samples from 68 individuals referred for laboratory investigation of suspected HNPCC. The V600E mutation was identified in 17 of 40 (42%) tumours showing loss of MLH1 protein expression by immunohistochemistry but in none of the 28 tumours that exhibited loss of MSH2 expression (P < 0.001). The assay was negative in all patients with an identified germline MMR gene mutation. Although biased by the fact that germline testing was not pursued beyond direct sequencing in many cases lacking a high clinical index of suspicion of HNPCC, BRAF V600E detection was therefore considered to be 100% specific and 48% sensitive in detecting sporadic MSI-H CRC amongst those cases showing loss of MLH1 protein expression, in a population of patients with MSI-H CRC and clinical features suggestive of HNPCC. Accordingly, we recommend the incorporation of BRAF V600E mutation testing into the laboratory algorithm for pre-screening patients with suspected HNPCC, whose CRCs show loss of expression of MLH1. In such tumours, the presence of a BRAF V600E mutation indicates the tumour is not related to HNPCC and that germline testing of MLH1 in that individual is not warranted. We also recommend that in families where the clinical suspicion of HNPCC is high, germline testing should not be performed on an individual whose CRC harbours a somatic BRAF mutation, as this may compromise identification of the familial mutation.

Effectiveness of the CRCAPRO program in identifying patients suspected for HNPCC

Subjects affected by hereditary non-polyposis colorectal cancer exhibit a high susceptibility to colon and extracolonic tumours, due to MMR gene defects. Revised Bethesda criteria are used to select patients as candidates for genetic tests. Recently, the CRCAPRO model has been developed, based on family history of colorectal and endometrial cancers. Our study aims to evaluate the reliability of CRCAPRO in identifying mutation carriers. We used the CRCAPRO program to evaluate carrier probability risk in 99 patients fulfilling Amsterdam or Bethesda guidelines. MLH1 and MSH2 were studied by direct sequencing in all the 99 patients, and the study of microsatellite instability and of MMR proteins expression was performed. Nine MLH1 and nine MSH2 germline mutations were identified. Five out of the nine patients with MLH1 mutation showed a CRCAPRO risk evaluation of less than 20%. The same happened for four out of nine patients with MSH2 mutation. Of the 17 patients with an estimated risk of more than 80%, only four harboured a mutation, all in the MSH2 gene. The highest risk calculated by the CRCAPRO system in the nine carriers of a MLH1 mutation has been 31.7%. In our experience, the CRCAPRO program sensitivity and specificity appears to be low but needs to be further evaluated in larger samples.

Assessing the Predictive Accuracy of hMLH1 and hMSH2 Mutation Probability Models

Hereditary nonpolyposis colorectal cancer (HNPCC) is characterized by a susceptibility to colorectal and extra-colonic cancers. Several guidelines exist for the identification of families suspected of having HNPCC, however these guidelines lack adequate sensitivity and specificity. In an attempt to improve accuracy for the detection of individuals with HNPCC, the Wijnen pre-test probability model (1998) and Myriad Genetics Laboratory prevalence table (2004) were developed. Here we evaluate the Wijnen model and Myriad table at predicting the presence of a mutation in individuals undergoing genetic testing for HNPCC. Forty-nine patients who had undergone genetic testing for germline mutations in hMLH1 and/or hMSH2 were part of our analysis. Our results revealed that the revised Bethesda guidelines performed with the highest sensitivity for germline mutations (94.4%), however the specificity was low (12.9%). Using a 10.0% mutation probability threshold, the Wijnen model and Myriad table had sensitivities of 55.6 and 60.0%, respectively and specificities of 54.8 and 23.8%, respectively. The Wijnen model and Myriad table were poor predictors of mutation prevalence, which is shown by the areas underneath their corresponding receiver operator characteristic curves (0.616 and 0.400, respectively). The results of this study demonsrate that neither the Wijnen model nor the Myriad table are sensitive or specific enough to be used as the only indication when to offer genetic testing for HNPCC.

Mismatch repair protein expression and microsatellite instability: a comparison of clear cell sarcoma of soft parts and metastatic melanoma

Clear cell sarcoma of soft parts is a rare soft tissue malignancy that shows phenotypic overlap with cutaneous melanoma but can be distinguished by the presence of a t(12;22) translocation. Microsatellite instability (MSI), a variation in the lengths of short repeat DNA segments in the genome, has been implicated in melanoma tumorigenesis, but is rare or absent in clear cell sarcoma. Defects in the mismatch repair (MMR) enzyme complex correlate with MSI in some tumor types, allowing the use of immunohistochemistry for the MMR proteins hMLH1 and hMSH2 to predict the presence of MSI. To determine if the association between MMR defects and MSI extends to clear cell sarcoma, we compared a group of nine clear cell sarcomas to 11 metastatic melanomas on the basis of MSI and the expression of MMR proteins. MSI was studied using fluorescence-based multiplexed PCR of five loci. Immunohistochemistry was evaluated on formalin-fixed paraffin-embedded tissue for hMLH1, hMHS2 and hMSH6. MSI was present in only 1/9 (11%) clear cell sarcoma case and in 8/11 (73%) melanoma cases. Immunostaining for hMLH1 and hMSH2 was preserved in all the clear cell sarcomas but loss of immunostaining for one or both proteins was seen in 6/11 melanomas (55%). hMSH6 was detected in 7/9 (78%) clear cell sarcomas and 10/11 (91%) of melanomas. Clear cell sarcoma and metastatic melanoma differed significantly with respect to the presence of MSI (P=0.010) and staining for hMLH1 and/or hMSH2 (P=0.014) but not hMSH6 (P=0.57). Mismatch repair, and consequently genomic instability may contribute to tumorigenesis in melanoma but not clear cell sarcoma. Immunostaining for hMLH1 and hMSH2 and MSI analysis may be helpful in the differential diagnosis of large soft tissue or visceral malignancies with melanocytic differentiation.

MUTYH Mutations Do Not Cause HNPCC or Late Onset Familial Colorectal Cancer

Recently, carriers of biallelic mutations in the base excision repair gene MUTYH, have been demonstrated to have a predisposition for multiple adenomas and colorectal cancer. Still, many questions remain unanswered concerning MUTYH. We have addressed the following: Do biallelic MUTYH mutation carriers invariably demonstrate FAP, and may MUTYH be a gene causing HNPCC, HNPCC-like or dominantly inherited late onset colorectal cancer? We examined affecteds from our total series of HNPCC, HNPCC-like and dominantly inherited late onset colorectal cancer kindreds not demonstrated to have any MMR mutations. Bloodsamples from 96 patients were subjected to sequencing of exon 7 and exon 13 in the MUTYH gene. Two heterozygotes and one homozygote for the European founder mutations were found. The homozygous carrier did not meet criteria for FAP/AFAP. We conclude that MUTYH, when mutated, causes a rare recessively inherited disorder including colorectal- and duodenal cancers. It is not verified that heterozygous carriers of MUTYH mutations have an increased risk of cancer, and they do not explain the occurrence of familial colorectal cancer in the population.

Molecular models for the tissue specificity of DNA mismatch repair-deficient carcinogenesis

A common feature of all the known cancer genetic syndromes is that they predispose only to selective types of malignancy. However, many of the genes mutated in these syndromes are ubiquitously expressed, and influence seemingly universal processes such as DNA repair or cell cycle control. The tissue specificity of cancers that arise from malfunction of these apparently universal traits remains a key puzzle in cancer genetics. Mutations in DNA mismatch repair (MMR) genes cause the most common known cancer genetic syndrome, hereditary non-polyposis colorectal cancer, and the fundamental biology of MMR is one of the most intensively studied processes in laboratories all around the world. This review uses MMR as a model system to understand mechanisms that may explain the selective development of tumors in particular cell types despite the universal nature of this process. We evaluate recent data giving insights into the specific tumor types that are attributable to defective MMR in humans and mice under different modes of inheritance, and propose models that may explain the spectrum of cancer types observed.