Challenges and pitfalls in HNPCC screening by microsatellite analysis and immunohistochemistry

Noninvasive detection of microsatellite instability in patients with endometrial cancer

The analysis of mismatch repair proteins in solid tissue is the standard of care (SoC) for the microsatellite instability (MSI) characterization in endometrial cancer (EC). Uterine aspirates (UAs) or circulating-DNA (cfDNA) samples capture the intratumor heterogeneity and provide a more comprehensive and dynamic molecular diagnosis. Thus, MSI analysis by droplet-digital PCR (ddPCR) in UAs and cfDNA can provide a reliable tool to characterize and follow-up the disease. The UAs, paraffin-embedded tumor tissue (FFPE) and longitudinal plasma samples from a cohort of 90 EC patients were analyzed using ddPCR panel and compared to the SoC. A high concordance (96.67%) was obtained between the analysis of MSI markers in UAs and the SoC. Three discordant cases were validated as unstable by ddPCR on FFPE samples. Besides, a good overall concordance (70.27%) was obtained when comparing the performance of the ddPCR assay on UAs and cfDNA in high-risk tumors. Importantly, our results also evidenced the value of MSI analysis to monitor the disease evolution. MSI evaluation in minimally invasive samples shows great accuracy and sensitivity and provides a valuable tool for the molecular characterization and follow-up of endometrial tumors, opening new opportunities for personalized management of EC.

Microsatellite instability profiles of gastrointestinal cancers: comparison between non-colorectal and colorectal origin

Microsatellite instability (MSI) is a major carcinogenic pathway with prognostic and predictive implications. The validity of polymerase chain reaction (PCR)-based MSI testing is well established in colorectal cancer; however, the data are limited in non-colorectal gastrointestinal cancers. The aim of this study is to clarify the detailed MSI profiles of non-colorectal gastrointestinal cancers and to investigate the differences from those of colorectal cancers. MSI testing was performed using paired tumour/normal tissues of 123 mismatch repair-deficient cancers detected by immunohistochemistry including 80 non-colorectal cancers (eight oesophagogastric junction (EGJ), 57 gastric and 15 small intestine) and 43 colorectal cancers. Fragment size analysis revealed that the mean nucleotide shifts of five markers (Promega panel) were the highest in the stomach (6.4), followed by colorectum (5.7), small intestine (5.0) and EGJ cancers (mean = 4.0; P = 0.015, versus stomach). All cases showed ≥ 1 nucleotide shift in ≥ 2 markers and were considered as MSI-high. However, when the cut-off was set to ≥ 3 nucleotide shifts in ≥ 2 markers, three EGJ (37.5%), two small intestine (13.3%) and two gastric (3.5%) cancers showed false-negative results. In addition, cases with isolated loss of MSH6 or PMS2 showed smaller nucleotide shifts than those in others. MSI testing is applicable to non-colorectal gastrointestinal cancers; however, a subset can yield false-negative results due to subtle nucleotide shift in multiple markers. Analysis of paired tumour/normal tissues and careful interpretation is necessary to avoid false-negative results and ensure appropriate treatment.

Cytoplasmic MSH2 Related to Genomic Deletions in the MSH2/EPCAM Genes in Colorectal Cancer Patients With Suspected Lynch Syndrome

Background

A large proportion of patients with Lynch syndrome (LS) have MSH2 abnormalities, but genotype-phenotype studies of MSH2 mutations in LS are still lacking. The aim of this study was to comprehensively analyze the clinicopathological characteristics and molecular basis of colorectal cancer (CRC) in patients with uncommon MSH2 cytoplasmic expression.

Methods

We retrospectively reviewed 4195 consecutive cases of CRC patients diagnosed between January 2015 and December 2017 at the Cancer Hospital Chinese Academy of Medical Sciences. Of the 4195 patients with CRC, 69 were indicated to have abnormal MSH2 expression through tumor immunohistochemical staining. Genetic tests, such as next-generation sequencing, large genomic rearrangement (LGR) analysis, microsatellite instability status analysis and genomic breakpoint analysis, were performed. Clinicopathological and molecular characteristics and clinical immunotherapy response were analyzed.

Results

Forty-five of 69 patients were identified to have LS with pathogenic germline mutations in MSH2 and/or EPCAM. Of these LS patients, 26.7% were confirmed to harbor large genomic rearrangements (LGRs). Of note, three tumors from two unrelated family pedigrees exhibited a rare cytoplasmic MSH2 staining pattern that was found in LS patients with EPCAM/MSH2 deletions. RNA analysis showed that two novel mRNA fusions of EPCAM and MSH2 resulted in the predicted protein fusion with MSH2 cytoplasmic localization. Analyses of genomic breakpoints indicated that two novel deletions of EPCAM and MSH2 originated from Alu repeat-mediated recombination events. Our study also provides clinical evidence for the beneficial effect of the PD-1 inhibitor pembrolizumab for CRC patients that exhibit cytoplasmic MSH2 staining.

Conclusion

Our study demonstrates that the rare cytoplasmic MSH2 staining pattern should be fully recognized by pathologists and geneticists. Given the specific genotype-phenotype correlation in LS screening, we advocate that all CRC patients with cytoplasmic MSH2 staining in histology should be screened for LGRs of EPCAM and MSH2.

Challenges of Neoantigen Targeting in Lynch Syndrome and Constitutional Mismatch Repair Deficiency Syndrome

Lynch syndrome (LS) and constitutional mismatch repair deficiency (CMMRD) are hereditary disorders characterised by a highly increased risk of cancer development. This is due to germline aberrations in the mismatch repair (MMR) genes, which results in a high mutational load in tumours of these patients, including insertions and deletions in genes bearing microsatellites. This generates microsatellite instability and cause reading frameshifts in coding regions that could lead to the generation of neoantigens and opens up avenues for neoantigen targeting immune therapies prophylactically and therapeutically. However, major obstacles need to be overcome, such as the heterogeneity in tumour formation within and between LS and CMMRD patients, which results in considerable variability in the genes targeted by mutations, hence challenging the choice of suitable neoantigens. The machine-learning methods such as NetMHC and MHCflurry that predict neoantigen- human leukocyte antigen (HLA) binding affinity provide little information on other aspects of neoantigen presentation. Immune escape mechanisms that allow MMR-deficient cells to evade surveillance combined with the resistance to immune checkpoint therapy make the neoantigen targeting regimen challenging. Studies to delineate shared neoantigen profiles across patient cohorts, precise HLA binding algorithms, additional therapies to counter immune evasion and evaluation of biomarkers that predict the response of these patients to immune checkpoint therapy are warranted.

The Mismatch Repair System (MMR) in Head and Neck Carcinogenesis and Its Role in Modulating the Response to Immunotherapy: A Critical Review

Simple Summary

The dysfunction of the mismatch repair system, an important mechanism for the detection and correction of DNA replication mistakes, may often lead to instability in the length of specific genetic sequences, known as microsatellites, and to the accumulation of mutations. Microsatellite instability is a well-known risk factor for the development of colorectal cancers and other types of tumors but is also considered a positive predictor of the immunotherapy response. Malignancies harboring such a specific genomic instability are very immunogenic because of the great number of aberrant antigens they produce. Therapies based on the blockade of specific immune checkpoints have shown to induce an effective immune response against microsatellite-unstable cancer. Many studies proved that microsatellite instability has a decisive role in the carcinogenesis and the malignant progression of head and neck cancer and, in the near future, it may become a useful tool in tailoring immunotherapy also in this field of precision oncology.

Abstract

The mismatch repair (MMR) system has a major role in the detection and correction of DNA replication errors, resulting from DNA polymerase slippage or nucleotides misincorporation. Specific inherited/acquired alterations or epigenetic inactivation of MMR genes are associated with microsatellite instability (MSI): the loss of crucial function in repairing DNA alterations can promote carcinogenesis by favoring the accumulation of thousands of mutations in a broad spectrum of different anatomic sites such as colon, stomach, prostate, esophagus, endometrium, lung and head and neck. Recent extensive data suggest that tumor mutational burden strongly correlates with a clinical response to immunotherapy using checkpoint inhibitors and this response is influenced by MMR deficiency in a wide range of human solid cancers. In this context, few data about this crucial point are available for head and neck cancer (HNC). In this review, we discuss the role of MMR alterations and the resulting MSI in HNC pathogenesis. Furthermore, by summarizing the clinical available data on how they influence the progression of precancerous lesions and the risk of recurrence or second primary tumors, we want to define the current role of MSI in the management of HNC. Finally, we analyze the complex interaction between cancer cells and the immune system addressing the data now available about a potential correlation between microsatellite instability and immunotherapy response in HNC.

A robust method for the rapid detection of microsatellite instability in colorectal cancer

Although several computational tools using next-generation sequencing (NGS) data have been proposed to detect microsatellite instability (MSI) status, they still have limitations and need improvement. We developed a NovoPM-MSI method to detect MSI status based on NGS data. This method evaluated target mononucleotide microsatellite loci that were sequenced during targeted gene enrichment analysis and reported sample instability score as the fraction of unstable loci within the target set after assessing locus instability by comparing length distribution in paired tumor-normal samples. We validated this method against the conventional MSI-PCR method in 113 paired colorectal cancer (CRC) specimens and compared the performance of NovoPM-MSI to that of mSINGS and MANTIS in accuracy and runtime efficiency. By using the MSI status from MSI-PCR as the gold standard, the three computational methods showed the same sensitivity of 88.9% but different specificities (NovoPM-MSI 97.1%, MANTIS 86.5% and mSINGS 99.0%). Only NovoPM-MSI could greatly improve both the sensitivity and specificity by setting an ambiguous interval. MANTIS had the shortest average runtime (16.3 sec), followed by NovoPM-MSI (18.3 sec) and mSINGS (109.0 sec). In short, the NovoPM-MSI method provides a fast and reliable MSI detection method with accuracy comparable to MSI-PCR in paired CRC samples.

The Cancer Immunotherapy Biomarker Testing Landscape

CONTEXT.—

Cancer immunotherapy provides unprecedented rates of durable clinical benefit to late-stage cancer patients across many tumor types, but there remains a critical need for biomarkers to accurately predict clinical response. Although some cancer immunotherapy tests are associated with approved therapies and considered validated, other biomarkers are still emerging and at various states of clinical and translational exploration.

OBJECTIVE.—

To provide pathologists with a current and practical update on the evolving field of cancer immunotherapy testing. The scientific background, clinical data, and testing methodology for the following cancer immunotherapy biomarkers are reviewed: programmed death ligand-1 (PD-L1), mismatch repair, microsatellite instability, tumor mutational burden, polymerase δ and ε mutations, cancer neoantigens, tumor-infiltrating lymphocytes, transcriptional signatures of immune responsiveness, cancer immunotherapy resistance biomarkers, and the microbiome.

DATA SOURCES.—

Selected scientific publications and clinical trial data representing the current field of cancer immunotherapy.

CONCLUSIONS.—

The cancer immunotherapy field, including the use of biomarker testing to predict patient response, is still in evolution. PD-L1, mismatch repair, and microsatellite instability testing are helping to guide the use of US Food and Drug Administration-approved therapies, but there remains a need for better predictors of response and resistance. Several categories of tumor and patient characteristics underlying immune responsiveness are emerging and may represent the next generation of cancer immunotherapy predictive biomarkers. Pathologists have important roles and responsibilities as the field of cancer immunotherapy continues to develop, including leadership of translational studies, exploration of novel biomarkers, and the accurate and timely implementation of newly approved and validated companion diagnostics.

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.

Accurate Pan-Cancer Molecular Diagnosis of Microsatellite Instability by Single-Molecule Molecular Inversion Probe Capture and High-Throughput Sequencing

BACKGROUND

Microsatellite instability (MSI) is an emerging actionable phenotype in oncology that informs tumor response to immune checkpoint pathway immunotherapy. However, there remains a need for MSI diagnostics that are low cost, highly accurate, and generalizable across cancer types. We developed a method for targeted high-throughput sequencing of numerous microsatellite loci with pan-cancer informativity for MSI using single-molecule molecular inversion probes (smMIPs).

METHODS

We designed a smMIP panel targeting 111 loci highly informative for MSI across cancers. We developed an analytical framework taking advantage of smMIP-mediated error correction to specifically and sensitively detect instability events without the need for typing matched normal material.

RESULTS

Using synthetic DNA mixtures, smMIPs were sensitive to at least 1% MSI-positive cells and were highly consistent across replicates. The fraction of identified unstable microsatellites discriminated tumors exhibiting MSI from those lacking MSI with high accuracy across colorectal (100% diagnostic sensitivity and specificity), prostate (100% diagnostic sensitivity and specificity), and endometrial cancers (95.8% diagnostic sensitivity and 100% specificity). MSI-PCR, the current standard-of-care molecular diagnostic for MSI, proved equally robust for colorectal tumors but evidenced multiple false-negative results in prostate (81.8% diagnostic sensitivity and 100% specificity) and endometrial (75.0% diagnostic sensitivity and 100% specificity) tumors.

CONCLUSIONS

smMIP capture provides an accurate, diagnostically sensitive, and economical means to diagnose MSI across cancer types without reliance on patient-matched normal material. The assay is readily scalable to large numbers of clinical samples, enables automated and quantitative analysis of microsatellite instability, and is readily standardized across clinical laboratories.

Differences in Microsatellite Instability Profiles between Endometrioid and Colorectal Cancers: A Potential Cause for False-Negative Results?

Colorectal (CRCs) and endometrioid (EMCs) cancers in patients with Lynch syndrome exhibit microsatellite instability (MSI) detected by PCR or immunohistochemistry (IHC). While both assays are equally sensitive for CRCs, some suggest that PCR has a higher false-negative rate than IHC in EMCs. We assessed the MSI profiles of 91 EMC and 311 CRC specimens using five mononucleotide repeat markers: BAT25, BAT26, NR21, NR24, and MONO27. EMCs with high MSI (MSI-H) showed a mean left shift of 3 nucleotides (nt), which was significantly different from 6 nt in CRCs. A shift of 1 nt was observed in multiple markers in 76% of MSI-H EMCs, whereas only 12% of MSI-H CRCs displayed a 1-nt shift in one of five markers. IHC against four mismatch repair proteins was performed in 78 EMCs. Loss of staining in one or more proteins was detected in 18 of 19 tumors that were MSI-H by PCR. When EMC tumor cell burden was diluted to <30%, MSI-H was no longer observed in two of three EMCs with a mean nucleotide shift of 1 nt. These results indicate that EMC and CRC MSI profiles are different and that caution should be exercised when interpreting the results, as subtle, 1-nt changes may be missed. These findings provide a potential cause of previously reported discordant MSI and IHC results in EMCs.

MSIplus for Integrated Colorectal Cancer Molecular Testing by Next-Generation Sequencing

Molecular analysis of colon cancers currently requires multiphasic testing that uses various assays with different performance characteristics, adding cost and time to patient care. We have developed a single, next-generation sequencing assay to simultaneously evaluate colorectal cancers for mutations in relevant cancer genes (KRAS, NRAS, and BRAF) and for tumor microsatellite instability (MSI). In a sample set of 61 cases, the assay demonstrated overall sensitivity of 100% and specificity of 100% for identifying cancer-associated mutations, with a practical limit of detection at 2% mutant allele fraction. MSIplus was 97% sensitive (34 of 35 MSI-positive cases) and 100% specific (42 of 42 MSI-negative cases) for ascertaining MSI phenotype in a cohort of 78 tumor specimens. These performance characteristics were slightly better than for conventional multiplex PCR MSI testing (97% sensitivity and 95% specificity), which is based on comparison of microsatellite loci amplified from tumor and matched normal material, applied to the same specimen cohort. Because the assay uses an amplicon sequencing approach, it is rapid and appropriate for specimens with limited available material or fragmented DNA. This integrated testing strategy offers several advantages over existing methods, including a lack of need for matched normal material, sensitive and unbiased detection of variants in target genes, and an automated analysis pipeline enabling principled and reproducible identification of cancer-associated mutations and MSI status simultaneously.

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.

Hereditary Syndromes Manifesting as Endometrial Carcinoma: How Can Pathological Features Aid Risk Assessment?

Endometrial carcinoma is the most common gynecological tumor worldwide. It can be the presenting malignancy, acting as the harbinger, of an undiagnosed hereditary syndrome. Up to 50% of females with Lynch syndrome present in this manner. Differentiation between Lynch, Muir-Torre, and Cowden syndromes can at times be challenging due to the overlapping features. Our review emphasizes on the strengths, pitfalls, and limitations of microscopic features as well as immunohistochemical and polymerase chain reaction- (PCR-) based tests used by laboratories to screen for DNA mismatch repair (MMR) and PTEN gene mutations in patients to enable a more targeted and cost effective approach in the use of confirmatory gene mutational analysis tests. This is crucial towards initiating timely and appropriate surveillance measures for the patient and affected family members. We also review the evidence postulating on the possible inclusion of uterine serous carcinoma as part of the spectrum of malignancies seen in hereditary breast and ovarian carcinoma syndrome, driven by mutations in BRCA1/2.

Detection of DNA mismatch repair (MMR) deficiencies by immunohistochemistry can effectively diagnose the microsatellite instability (MSI) phenotype in endometrial carcinomas

BACKGROUND

A proportion of endometrial carcinomas (ECs) are associated with deficient DNA mismatch repair (MMR). These tumors are characterized by high levels of microsatellite instability (MSI). Identification of MSI is important in identifying women who should be tested for Lynch syndrome and identifying a phenotype that may have specific prognostic and predictive implications. Genomic characterization of ECs has shown that MSI tumors form a distinct subgroup. The two most common methodologies for MSI assessment have not been compared in EC.

METHODS

Pentaplex mono and di-nucleotide PCR for MSI testing was compared to MMR IHC (presence/absence of MLH1, MSH2, MSH6, PMS2) in a cohort of patients with EC. Concordance, Kappa statistic, sensitivity, specificity, positive and negative predictive values were obtained on the cross-tabulation of results.

RESULTS

Comparison of both MSI and MMR status was complete for 89 cases. Overall agreement between methods (concordance) was 93.3% (95% CI[85.9%-97.5%]). A one-sided test to determine whether the accuracy is better than the "no information rate," which is taken to be the largest class percentage in the data, is significant (p<0.00001). Unweighted Kappa was 0.84, along with the sensitivity (88.5%), specificity (95.2%), PPV (88.5%), and NPV (95.2%). The balanced accuracy (i.e. the average between sensitivity and specificity) was 92%.

DISCUSSION

We show the equivalence of MSI testing and MMR IHC. We advocate the implementation of MMR IHC in future EC classification schemes, enabling stratification of cases for future clinical trials as well as assisting identification of Lynch syndrome, so that screening and risk reducing interventions can be undertaken.

Heterogenous mismatch-repair status in colorectal cancer

Abstract

Virtual Slides

The virtual slide(s) for this article can be found here: http://www.diagnosticpathology.diagnomx.eu/vs/1771940323126788

Expression analysis of heat shock protein 90 (HSP90) and Her2 in colon carcinoma

PURPOSE

The molecular chaperone heat shock protein 90 (HSP90) plays an important role in several types of tumors also participating in the modulation of the activity of receptor tyrosine kinases activity such as members of the Her family. We evaluated the significance of HSP90 and Her2 expression in colon cancer.

METHODS

HSP90 and Her2 expression was determined by immunohistochemistry and by fluorescence in situ hybridization (FISH) on 355 primary resected colon carcinomas. Results were correlated with pathologic features (Union for International Cancer Control (UICC) pTNM category, tumor localisation, tumor differentiation), additional molecular genetic characteristics (BRAF, KRAS mutational status, mismatch repair genes (MMR)), and survival.

RESULTS

HSP90 immunoreactivity was observed in various degrees. Fifty-one cases (14 %) were positive for Her2 (score 2+ and 3+) with 16/43 cases with Her2 2+ staining pattern showing amplification of Her2 determined by FISH. There was a significant correlation between high HSP90 expression and Her2 overexpression (p = 0.011). High HSP90 expression was associated with earlier tumor stages (p = 0.019), absence of lymph node (p = 0.006), and absence of distant metastases (p = 0.001). Patients with high tumoral HSP90 levels had a better survival (p = 0.032), but this was not independent from other prognostic relevant pathologic parameters. Her2 expression was not associated with any of the investigated histopathological, molecular, or clinical parameters.

CONCLUSIONS

High HSP90 levels are reflecting lower malignant potential in colon cancer. Her2 positivity can be observed in a small number of cases. Targeting HSP90 and/or Her2 may be an alternative therapeutic approach in colon cancer in a subset of patients.

Loss of expression of DNA mismatch repair proteins in aberrant crypt foci identified in vivo by magnifying colonoscopy in subjects with hereditary nonpolyposic and sporadic colon rectal cancer

PURPOSE

The aims of this study are to characterize the frequency, density, and distribution of aberrant crypt foci (ACF) and its histological features and to determine the frequency of loss of expression of DNA mismatch repair (MMR) proteins of subjects with hereditary nonpolyposic colorectal cancer (HNPCC) and sporadic colon rectal cancer (CRC).

METHODS

Patients with HNPCC, first-degree relatives of subjects with HNPCC, sporadic CRC, and average risk subjects of sporadic CRC were included prospectively. Total colonoscopy with chromoendoscopy using methylene blue 0.5% and magnification in the right colon (cecum and 20 cm of the ascending colon) and in the left colon (rectum) was performed; loss of expression of MLH1 and MSH2 was evaluated by immunohistochemistry in confirmed ACF.

RESULTS

Fifty-two subjects were included. Thirty-eight of the 119 ACF detected by endoscopy were biopsied. In 14 of the 38 specimens (36.8%), ACF were confirmed by histology (Cohen's kappa, 0.44). In subjects with HNPCC, ACF were identified more frequently in the right segment of the colon than in the left (73.1% vs. 26%); in contrast, ACF predominated in the left segment of the colon (89.3% vs. 10.6%) in subjects with sporadic CRC. There was a loss of MLH1 expression in ACF in subjects with HNPCC.

CONCLUSIONS

In HNPCC, we found a greater density of ACF in the right colon, and in sporadic CRC, greater density in the left. ACF present loss in the expression of DNA MMR protein and can be used as an early marker in patients with a risk of HNPCC in whom carcinogenesis appears to be accelerated.

Anticipation in lynch syndrome: where we are where we go

Lynch syndrome (LS) is the most common form of inherited predisposition to develop cancer mainly in the colon and endometrium but also in other organ sites. Germline mutations in DNA mismatch repair (MMR) gene cause the transmission of the syndrome in an autosomal dominant manner. The management of LS patients is complicated by the large variation in age at cancer diagnosis which requires these patients to be enrolled in surveillance protocol starting as early as in their second decade of life. Several environmental and genetic factors have been proposed to explain this phenotypic heterogeneity, but the molecular mechanisms remain unknown. Although the presence of genetic anticipation in Lynch syndrome has been suspected since 15 years, only recently the phenomenon has been increasingly reported to be present in different cancer genetic syndromes including LS. While the biological basis of earlier cancer onset in successive generations remains poorly known, recent findings point to telomere dynamics as a mechanism significantly contributing to genetic anticipation in Lynch syndrome and in other familial cancers. In this review, we summarize the clinical and molecular features of Lynch syndrome, with a particular focus on the latest studies that have investigated the molecular mechanisms of genetic anticipation.

Lynch syndrome: clinical, pathological, and genetic insights

INTRODUCTION

Lynch syndrome as the most common hereditary colorectal cancer syndrome and the most common cause of hereditary endometrial cancer is characterized by an autosomal dominant inheritance with a penetrance of 85-90%. The molecular genetic underlying mechanism is a mutation in one of the mismatch repair genes.

METHODS

In order to identify patients with Lynch syndrome, a nuclear family history should be ascertained and matched with the Amsterdam criteria. A different approach for identification is the adherence to Bethesda criteria and subsequent testing for microsatellite instability. In patients with unstable tumors as an indicator for mismatch repair deficiency, genetic counseling and mutation analysis are warranted. For families fulfilling the Amsterdam criteria, intensified screening is recommended, even if a pathogenic mutation is not identified.

RESULTS

Individuals from families with a proven pathogenic mutation that are tested negative are at normal population risk for cancers and may be dismissed from intensified surveillance. Prophylactic surgery in high-risk individuals without neoplasia is not generally recommended. At the time of a colon primary, however, extended surgery should be discussed in the light of a high rate of metachronous cancers. The worries of impairing functional results have now been evaluated in the light of quality of life in a large international cohort. Interestingly, extended (prophylactic) surgery does not lead to inferior quality of life with equal perioperative risks.

CONCLUSIONS

Therefore, taking the risk reduction into account, extended surgery at the time of the first colon primary should at least be discussed, if not recommended. Also, prophylactic hysterectomy and bilateral oophorectomy at the time of a colorectal primary should be recommended if family planning has been completed.

Identification of individuals at risk for Lynch syndrome using targeted evaluations and genetic testing: National Society of Genetic Counselors and the Collaborative Group of the Americas on Inherited Colorectal Cancer joint practice guideline

Identifying individuals who have Lynch syndrome (LS) involves a complex diagnostic work up that includes taking a detailed family history and a combination of various genetic and immunohistochemical tests. The National Society of Genetic Counselors (NSGC) and the Collaborative Group of the Americas on Inherited Colorectal Cancer (CGA-ICC) have come together to publish this clinical practice testing guideline for the evaluation of LS. The purpose of this practice guideline is to provide guidance and a testing algorithm for LS as well as recommendations on when to offer testing. This guideline does not replace a consultation with a genetics professional. This guideline includes explanations in support of this and a summary of background data. While this guideline is not intended to serve as a review of LS, it includes a discussion of background information on LS, and cites a number of key publications which should be reviewed for a more in-depth understanding of LS. These guidelines are intended for genetic counselors, geneticists, gastroenterologists, surgeons, medical oncologists, obstetricians and gynecologists, nurses and other healthcare providers who evaluate patients for LS.

DNA mismatch repair enzyme immunohistochemistry in colorectal cancer: a comparison of biopsy and resection material

BACKGROUND

Microsatellite instability (MSI) in colorectal cancer (CRC) may be predicted using mismatch repair protein (MMRP) immunohistochemistry (immunostaining), allowing focused genetic investigations and potentially influencing therapeutic interventions. Most laboratories perform immunostaining on surgical resection specimens. Endoscopic biopsy specimens are an alternative tissue source for immunostaining. Given the sensitivity of immunostaining to the degree of tissue fixation, endoscopic biopsy material may produce superior staining, based on faster and more thorough fixation. Moreover, in patients receiving neoadjuvant chemotherapy and/or radiotherapy, endoscopic biopsies may be more useful than surgical resection specimens by allowing assessment of MMR status prior to chemotherapy and/or radiotherapy induced changes in tumours. This study examines whether immunostaining for MMRP expression in CRC is as reliable on endoscopic biopsy material as on surgical resection specimens.

METHODS

Immunostaining for MLH1, PMS2, MSH2 and MHS6 was performed on 112 unselected CRC cases with both endoscopic biopsy and surgical resection material available. A single observer blindly examined intensity and distribution of staining and assessed MMRP expression. Two consultant histopathologists reviewed challenging cases. Endoscopic biopsies and surgical resections were compared using non-parametric statistical analysis.

RESULTS

Immunostaining for all four MMRPs on all 112 cases produced conclusive (i.e., fully interpretable) results in endoscopic biopsies. In surgical resection specimens, 10 stains from nine cases were inconclusive (stains for two MMRPs were inconclusive in one case). In cases where conclusive immunostaining was achieved, there was complete agreement in MMRP status between the endoscopic biopsy and corresponding surgical resection specimens. Overall, MMRP loss was identified in 13% of cases; 11% MLH1, 12% PMS2, 1% MSH2, and 1% MSH6. Immunostaining intensity was significantly higher (p < 0.0005) and the distribution of staining was significantly more uniform (p < 0.0005) on endoscopic biopsy than on surgical resection.

CONCLUSION

Endoscopic biopsy provides equal accuracy and easier interpretation of MMRP expression immunostaining compared to surgical resection specimens.

Genetic counseling considerations in the evaluation of families for Lynch syndrome--a review

Lynch syndrome is the most common hereditary colorectal cancer syndrome and the most common cause of hereditary endometrial cancer. Identifying and evaluating families for Lynch syndrome is increasing in complexity due to the recognition that: family history-based clinical criteria lack sensitivity and specificity; genetic testing for Lynch syndrome continues to evolve as understanding of the molecular mechanisms underlying it evolves; and the Lynch syndrome phenotype encompasses multiple organ systems and demonstrates overlap with other hereditary cancer syndromes. This document is a summary of considerations when evaluating individuals and families for Lynch syndrome, including information on cancer risks, diagnostic criteria, tumor and genetic testing strategies, and the management of individuals with this condition.

Interobserver variability in the evaluation of mismatch repair protein immunostaining

Immunohistochemical staining for mismatch repair proteins has during recent years been established as a routine analysis in many pathology laboratories with the aim to identify tumors linked to the hereditary nonpolyposis colorectal cancer syndrome. Despite widespread application, data on reliability are lacking. We therefore evaluated interobserver variability among 6 pathologists, 3 experienced gastrointestinal pathologists and 3 residents. In total, 225 immunohistochemically stained colorectal cancers were evaluated as having normal, weak, loss of, or nonevaluable mismatch repair protein staining. Full consensus was achieved in 51% of the stainings for MLH1, 61% for PMS2, 83% for MSH2, and 45% for MSH6. Weak stainings were the main cause of reduced consensus, whereas contradictory evaluations with normal as well as loss of staining were reported in 2% to 6% of the tumors. Interobserver variability was considerable, though experienced pathologists and residents reached the same level of consensus. Because results from immunohistochemical mismatch repair protein stainings are used for decisions on mutation analysis and as an aid in the interpretation of gene variants of unknown significance in hereditary nonpolyposis colorectal cancer, the interobserver variability identified highlights the need for quality assessment programs, including guidelines for classification of different expression patterns.

A review on the molecular diagnostics of Lynch syndrome: a central role for the pathology laboratory

Lynch syndrome (LS) is caused by mutations in mismatch repair genes and is characterized by a high cumulative risk for the development of mainly colorectal carcinoma and endometrial carcinoma. Early detection of LS is important since surveillance can reduce morbidity and mortality. However, the diagnosis of LS is complicated by the absence of a pre-morbid phenotype and germline mutation analysis is expensive and time consuming. Therefore it is standard practice to precede germline mutation analysis by a molecular diagnostic work-up of tumours, guided by clinical and pathological criteria, to select patients for germline mutation analysis. In this review we address these molecular analyses, the central role for the pathologist in the selection of patients for germline diagnostics of LS, as well as the molecular basis of LS.

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.

Reduced mRNA expression in paraffin-embedded tissue identifies MLH1- and MSH2-deficient colorectal tumours and potential mutation carriers

Based on the principle of nonsense-mediated mRNA decay, we sought to identify MLH1 or MSH2-deficient colorectal tumours through relative quantification of mRNA expression with real-time PCR (RT-PCR) analysis. MLH1 and MSH2 mRNAs were almost equally expressed as defined by MLH1 to MSH2 transcript ratio (mean 1.41) in microsatellite stable, mismatch repair (MMR) proficient tumours (n = 16). A close correlation between loss of protein expression and MMR-mRNA levels was found in highly microsatellite instable (MSI-H) tumours deficient of MLH1 or MSH2. MLH1/MSH2 ratio was low in 11 sporadic and nine hereditary MLH1-deficient carcinomas (mean 0.51), whereas the ratio was high in 17 MSH2-deficient hereditary non-polyposis colorectal cancer (HNPCC) associated carcinomas (mean 6.8). Notably, in the normal tissues of HNPCC patients with MSH2 mutations, the MLH1/MSH2 transcript ratios were significantly elevated (ratio > 2.0) as compared to the ratios of normal mucosa in patients with MMR-proficient tumours (27 of 32 ratio < 2.0; p = 0.00113). Analysis of B-lymphocytes of HNPCC patients with proven MMR gene mutation confirmed these findings. In conclusion, RT-PCR allows relative quantification of MMR gene mRNA expression in formalin-fixed and paraffin-embedded tissue. Furthermore, this approach enables quantification of haploinsufficiency due to nonsense-mediated mRNA decay in normal tissue and B-lymphocytes from patients carrying MSH2 germline mutations and may be useful for identification of asymptomatic carriers of pathogenic germline mutations.

Colorectal adenomas in young patients: microsatellite instability is not a useful marker to detect new cases of Lynch syndrome

PURPOSE

Original Bethesda Guidelines proposed microsatellite instability analysis in colorectal adenomas from patients younger than aged 40 years to identify new cases of Lynch syndrome. We intended to evaluate the characteristics of colorectal adenomas from patients younger than aged 40 years to determine their microsatellite instability status and to correlate it with germline mutations in MLH1 and MSH2 genes.

METHODS

Seventy-two adenomas from 58 patients were analyzed. Family history of colorectal cancer, location, and histology of adenomas were evaluated. Microsatellite instability testing was performed with BAT26 only or with the complete Bethesda panel. Germline mutational analysis was performed in MLH1 and MSH2 genes.

RESULTS

Thirty-five patients had a family history of colorectal cancer and 16 of them belonged to Amsterdam Criteria positive families. The remaining 23 presented with sporadic adenomas. Microsatellite instability was found in seven adenomas from seven different patients, all belonging to Amsterdam Criteria-positive families. In six of these patients, a pathogenic germline mutation was identified.

CONCLUSIONS

Adenomas diagnosed before aged 40 years presented microsatellite instability only in patients from families with clinical criteria for Lynch syndrome. According to our results, to detect new cases of Lynch syndrome, family history is more important than microsatellite instability testing in adenomas from young patients.

Mismatch repair protein expression in Amsterdam II criteria-positive patients in Taiwan

BACKGROUND

Hereditary non-polyposis colorectal cancer (HNPCC) is characterized genetically by germline mutations in DNA mismatch repair (MMR) genes. Immunohistochemistry (IHC) has high sensitivity and specificity for identifying MMR-deficient tumours. This study investigated the clinical presentations and frequency of HNPCC in Taiwan by combined Amsterdam II criteria (AC-II) and IHC.

METHODS

In 1995-2003, 7108 patients with primary colorectal cancer registered in Chang Gung Memorial Hospital's Colorectal Cancer Registry were screened using AC-II. Tumour specimens were analysed for MMR protein expression by IHC, and relevant clinicopathological details were documented.

RESULTS

Some 83 patients fulfilled the AC-II. Clinicopathologically, 43 patients (52 per cent) had proximal tumours, ten (12 per cent) had poorly differentiated cancers, 17 (20 per cent) had mucinous adenocarcinoma and 51 (61 per cent) had stage I-II tumours. Seventeen patients developed second primary colonic and extracolonic cancers over a mean 7.2-year follow-up. Immunohistochemically, 58 patients were MMR protein deficient. They had a significantly earlier age of onset (P < 0.001), more proximal tumour location (P = 0.002), less advanced tumour stage (P = 0.008) and more second primary cancers (P = 0.017) compared with MMR-competent patients.

CONCLUSION

These data show significant differences in clinical features between MMR protein-deficient and MMR competent subgroups.

Molecular testing for microsatellite instability and its value in tumor characterization

Molecular analysis of tumor tissue has become a rapidly expanding field in medical research, exploiting the advantages of new technologies adapted to high-throughput examination of genetic alterations, gene and protein expression patterns. Only exceptionally, these approaches have found their way into routine clinical diagnosis and therapy. Microsatellite instability testing has been established as a very powerful tool to identify patients with hereditary nonpolyposis colorectal cancer, one of the most common familial cancer syndromes. In addition, there is emerging evidence that microsatellite instability analysis may become increasingly important for the clinician, having considerable impact on patients' prognosis as well as therapeutic decisions, at least in colorectal cancer patients. A better understanding of the microsatellite instability phenotype, its pathogenesis and implications for the course of the disease will pave the way for novel diagnostic and therapeutic strategies specifically tailored to microsatellite-unstable tumors. This review summarizes the current significance of molecular testing for microsatellite instability in several tumor entities and provides prospects of future developments.

The additive effect of p53 Arg72Pro and RNASEL Arg462Gln genotypes on age of disease onset in Lynch syndrome patients with pathogenic germline mutations in MSH2 or MLH1

p53 and the prostate-cancer-susceptibility gene RNASEL are tumour suppressor genes involved in apoptosis. We have previously reported that the common, functionally different variants Arg72Pro in p53 and Arg462Gln in RNASEL are associated with the age of disease onset of colorectal cancer in Lynch syndrome patients. To assess the combined effect of both variants, we screened 246 unrelated Lynch syndrome patients with a pathogenic germline mutation either in MSH2 (n=138) or in MLH1 (n=108) and colorectal cancer as first tumour, and 245 healthy controls. The global log rank test revealed significant differences in the age of disease onset for the genotypes of each variant (p=0.0176 for p53 and p=0.0358 for RNASEL) and for the combined genotypes of both variants (p=0.0174). The highest difference in median age of disease onset was seen between homozygotes for the wild-types in both genes (42years [range 22-75]) and homozygotes for the variant alleles in both genes (30years [range 26-47]). A multivariate Cox regression model indicated that only the p53 and RNASEL genotypes had a significant influence on age of disease onset (p=0.016 for p53 and p=0.014 for RNASEL) in an additive mode of inheritance, and that the effects of both variants are purely additive, which supports the notion that the p53 and RNaseL pathways do not interact. These findings may be relevant for preventive strategies in Lynch syndrome.

Genetic testing for colon cancer

Colon cancer remains the third leading cause of death due to cancer in the US, where it affected more than 145,000 individuals in 2005. Up to 30% of these cases exhibit familial clustering, which means that tens of thousands of individuals have a disease with a potentially definable genetic component. Approximately 3-5% of colon cancers are associated with high-risk, inherited colon cancer syndromes. Identification of the genes that cause these colon cancer syndromes, coupled with additional insights into their clinical course, has led to the development of specific management guidelines--and genetic tests--that can diagnose these familial disorders. These guidelines can be life-saving, not only for the affected patient, but also for their family members.

Prevalence of the mismatch-repair-deficient phenotype in colonic adenomas arising in HNPCC patients: results of a 5-year follow-up study

In hereditary nonpolyposis colorectal cancer (HNPCC) syndrome, more than 90% of the carcinomas show microsatellite instability (MSI) due to a loss of mismatch repair (MMR) function. Although adenomas are very common in HNPCC and demonstrate an accelerated adenoma-carcinoma sequence, data about the prevalence and development of MSI in these early neoplastic lesions are lacking. To determine whether MSI and loss of MMR-protein expression are already present in early stages of tumorigenesis and could therefore be used as a screening tool to identify HNPCC patients before they develop an invasive carcinoma, we analyzed 71 adenomas of 36 HNPCC patients during a 5-year follow-up study. These 36 patients were part of a cohort of 122 HNPCC patients who were investigated at the Institute of Pathology, Klinikum Kassel, as part of the multicentric German HNPCC Consortium, which currently serves more than 2,880 registered families. The diagnosis of HNPCC was based either on the detection of a pathogenic germline mutation in the MSH2, MLH1, or MSH6 genes or in cases where a pathogenic mutation was not found; diagnosis of HNPCC was made, because all patients fulfilled the Amsterdam or Bethesda criteria and revealed a high degree of MSI (MSI-H) as well as loss of one of the MMR proteins by IHC in the cancer tissue. We found that most adenomas (58/71) were MSI-H and had loss of MMR-protein expression. Of the 71 adenomas, 3 were MSI-H with expression of all MMR proteins, and 3 out of 71 displayed loss of a MMR protein with the microsatellites being classified as microsatellite stable (MSS). However, 7 of the 31 adenomas that were located more than 5 cm away from the carcinoma revealed an MSS status (n=6) or low in MSI (n=1) and expressed all MMR proteins. In summary, a significant percentage of HNPCC-associated adenomas (7/31, 22.6%) developing at a distance of more than 5 cm from the corresponding carcinoma did not show the MSI-H MMR-deficient phenotype and expressed all MMR genes. To our knowledge, this is the first study that shows that in most HNPCC patients, the mutator pathway is already detectable in adenomas, but MMR-proficient adenomas can also be found. Therefore, screening for MMR deficiency should not be applied routinely in adenomas with the goal to identify HNPCC patients.

Novel strategy for optimal sequential application of clinical criteria, immunohistochemistry and microsatellite analysis in the diagnosis of hereditary nonpolyposis colorectal cancer

Clinical criteria, microsatellite analysis (MSA) and immunohistochemistry (IHC) are important diagnostic tools for identification of hereditary nonpolyposis colorectal cancer (HNPCC) patients who are likely to carry pathogenic germline mutations in mismatch repair genes. Based on MSA and IHC results and subsequent mutation analyses of 1,119 unrelated index patients meeting the Amsterdam II criteria or the classical Bethesda guidelines, we analyzed the value of these tools to predict MLH1 and MSH2 mutations with the aim of establishing optimal strategies for their most efficient sequential use. The overall prevalence of pathogenic germline mutations in our cohort was 20.6% (95% CI = 18.3-23.0%) and 61.8% (95% CI = 56.8-66.6%), respectively, after MSA/IHC-based preselection. IHC was highly predictive (99.1%) and specific (99.6%) with regard to MSA. However, 14 out of 230 mutations (6%) escaped detection by IHC. Thus, IHC cannot be recommended to substitute MSA fully. Nonetheless, IHC is important to indicate the gene that is likely to be affected. To combine both methods efficiently, we propose a novel screening strategy that provides 2 alternative ways of sequential IHC and MSA application, either using IHC or MSA in the first place. A logistic regression model based on the age of the index patient at first tumor diagnosis and the number of fulfilled HNPCC criteria is used to allocate individual patients to that alternative pathway that is expected to be least expensive. A cost analysis reveals that about 25% of the costs can be saved using this strategy.

Arg462Gln sequence variation in the prostate-cancer-susceptibility gene RNASEL and age of onset of hereditary non-polyposis colorectal cancer: a case-control study

BACKGROUND

RNASEL is thought to be a susceptibility gene for hereditary prostate cancer and encodes the endoribonuclease RNase L, which has a role in apoptosis and is a candidate tumour-suppressor protein. A common sequence variation in RNASEL, Arg462Gln, has been associated with hereditary and sporadic prostate cancer, and the Gln variant has about three-fold reduced RNase activity in vitro. In view of the association between the age of onset of hereditary non-polyposis colorectal cancer and functionally different variants of P53, which play a key part in the apoptotic pathway, we aimed to assess whether the Arg462Gln variation of RNASEL affects the age of onset of hereditary non-polyposis colorectal cancer.

METHODS

We screened 251 patients with hereditary non-polyposis colorectal cancer who were unrelated, had pathogenic germline mutations in MSH2 (n=141) or MLH1 (n=110), and had colorectal carcinoma as the first tumour, for variation at codon 462 of RNASEL and compared them with 439 healthy controls.

FINDINGS

The median age of onset was 40 years (range 17-75) for patients with an Arg/Arg genotype at codon 462, 37 years (13-69) for patients with an Arg/Gln genotype, and 34 years (20-49) for those with a Gln/Gln genotype (p=0.0198). Only the RNASEL genotype had a significant effect on age of onset (p=0.0062) in an additive mode of inheritance. Pair-wise comparisons between genotype groups showed that the two homozygous groups (ie, Arg/Arg vs Gln/Gln) differed significantly in age of disease onset (mean age difference 4.8 years [SD 1.7], p=0.0044).

INTERPRETATION

A sequence variation in the prostate-cancer-susceptibility gene RNASEL has a role in a different, unassociated malignant disease. Genotypes at RNASEL codon 462 are associated with age of onset of hereditary non-polyposis colorectal cancer in a dose-dependent way, and might have a role in preventive strategies for this disease.

Genetic testing for inherited colon cancer

The genes associated with each of the inherited syndromes of colon cancer have now been identified, and genetic testing is available for diagnosis. These syndromes include familial adenomatous polyposis, hereditary nonpolyposis colorectal cancer, Peutz-Jeghers syndrome, juvenile polyposis syndrome, and, possibly, Cowden's syndrome. Clinical genetic testing approaches have been developed for each of these syndromes and are now a part of accepted clinical care. Disease-causing mutations can be found in the majority of families affected with one of the inherited syndromes, and, most importantly, once a mutation is found in an index case of the family, relatives can be tested for the presence or absence of that mutation with near 100% accuracy. Cancer screening and management in syndrome families is then based on the results of genetic testing. For the physician to order and properly interpret genetic tests, a basic understanding of the types of mutations that lead to inherited disease and the methods for detecting them is vital. These issues will be presented. Additional clinical issues somewhat unique to genetic testing include genetic counseling and informed consent for genetic testing, both of which will also be reviewed. Often the most difficult aspect of genetic testing is deciding which patients and families should undergo the testing. Furthermore, this issue is quite specific for each of the syndromes. Thus, following presentation of general principles of selection for genetic testing, a detailed approach for identifying persons who should undergo testing for each of the individual syndromes will be given, together with relevant descriptions of the syndromes. Finally, the ongoing work to discover new and possibly more common but less penetrant colon cancer susceptibility genes that cause common familial colon cancer will be presented.

Microsatellite analysis of hereditary nonpolyposis colorectal cancer-associated colorectal adenomas by laser-assisted microdissection: correlation with mismatch repair protein expression provides new insights in early steps of tumorigenesis

Although microsatellite instability (MSI) testing is a useful tool for molecular screening of hereditary nonpolyposis colorectal cancer (HNPCC) carcinomas, conflicting results have been obtained in colorectal adenomas. This might result from different techniques of tissue sampling and MSI analysis. Alternatively, some HNPCC-associated adenomas may follow a molecular route that differs from the MSI pathway. In the present study we examined the MSI status of 18 adenomas from 17 HNPCC patients by comparing manual adenoma dissection under gross visual control with laser microdissection of single adenoma crypts. After manual gross dissection, 50% (9 of 18) and 11.1% (2 of 18) of the adenomas displayed high-level (MSI-H) and low-level (MSI-L) MSI, respectively. The same set of adenomas split into 83.3% (15 of 18) MSI-H and 5.6% (1 of 18) MSI-L after laser microdissection. The expression pattern of mismatch repair (MMR) proteins showed a higher concordance rate with the MSI status in laser-dissected (94%) than gross-dissected (47%) adenomas. Whereas two adenomas remained microsatellite stable (MSS) and MMR proficient even after laser-assisted dissection, two MSI-H cases showed either rare instabilities at coding microsatellites or intratumoral heterogeneity of MSI with and without MSH2 expression. This suggests that in some adenomas development of MMR dysfunction occurs stepwise with MSI, arising before complete loss of MMR gene expression, whereas other HNPCC-associated adenomas might develop independently of MMR deficiency.