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The Evaluation of Genomic Applications in Practice and Prevention (EGAPP) Working Group found sufficient evidence to recommend offering genetic testing for Lynch syndrome to individuals with newly diagnosed colorectal cancer to reduce morbidity and mortality in relatives. We found insufficient evidence to recommend a specific genetic testing strategy among the several examined.
Genetic testing to detect Lynch syndrome in individuals with newly diagnosed colorectal cancer (CRC) is proposed as a strategy to reduce CRC morbidity and mortality in their relatives (see Clinical Considerations section for definition of Lynch syndrome). The EGAPP Working Group (EWG) constructed a chain of evidence that linked genetic testing for Lynch syndrome in patients with newly diagnosed CRC with improved health outcomes in their relatives. We found that assessing patients who have newly diagnosed CRC with a series of genetic tests could lead to the identification of Lynch syndrome. Relatives of patients with Lynch syndrome could then be offered genetic testing, and, where indicated, colorectal, and possibly endometrial, cancer surveillance, with the expectation of improved health outcome. The EWG concluded that there is moderate certainty that such a testing strategy would provide moderate population benefit.
The EWG found adequate evidence to conclude that the analytic sensitivity and specificity for preliminary and diagnostic tests were high.
After accounting for the specific technologies and numbers of markers used, the EWG found at least adequate evidence to describe the clinical sensitivity and specificity for three preliminary tests, and for four selected testing strategies. These measures of clinical validity varied with each test and each strategy (see Clinical Considerations section).
The EWG found adequate evidence for testing uptake rates, adherence to recommended surveillance activities, number of relatives approachable, harms associated with additional follow-up, and effectiveness of routine colonoscopy. This chain of evidence supported the use of genetic testing strategies to reduce morbidity/mortality in relatives with Lynch syndrome. Several genetic testing strategies were potentially effective, but none was clearly superior. The evidence for or against effectiveness of identifying mismatch repair (MMR) gene mutations in reducing endometrial cancer morbidity or mortality was inadequate.
CRC is a common disease responsible for an estimated 52,000 deaths in the United States in 2007. In about 3% of newly diagnosed CRC, the underlying cause is a mutation in a MMR gene (Lynch syndrome) that can be reliably identified with existing laboratory tests. Relatives inheriting the mutation have a high (about 45% by age 70) risk of developing CRC. Evidence suggests these relatives will often accept testing and increased surveillance.
These recommendations apply to all individuals with a new diagnosis of CRC. An estimated 2–4% can be identified as having Lynch syndrome.
Microsatellite instability (MSI) testing or immunohistochemical (IHC) testing (with or without BRAF mutation testing) of the tumor tissue are examples of preliminary testing strategies that could be used to select patients for subsequent diagnostic testing. Diagnostic testing involves MMR gene mutation (and deletion/duplication) testing of the proband, usually using a blood sample. Lynch syndrome is most commonly caused by mutations in the two MMR genes MLH1 and MSH2; less commonly by mutations in MSH6 and PMS2.
Clinical performance (sensitivity/specificity) to identify Lynch syndrome:
Evidence does not exist to make specific recommendations for changes in CRC treatment in probands. The EWG recommends that probands be informed of the advantages of contacting blood relatives to offer counseling and targeted testing to diagnose Lynch syndrome. Among relatives diagnosed with Lynch syndrome (MMR positive), more frequent colonoscopies are indicated and should begin at an earlier age than recommended for average risk individuals. Increased surveillance results in reduced rates of colon cancer and death from all causes. Among women with Lynch syndrome (both probands and relatives), additional surveillance for early identification of endometrial cancer may be considered, but there is less evidence to support it.
Family history is an important risk factor for CRC in the general population. Among individuals with newly diagnosed CRC, however, family history is less useful as the first step in identifying Lynch syndrome than strategies involving the analysis of tumor samples (e.g., MSI, IHC). The application of Amsterdam and Bethesda criteria has resulted in variable and generally poor performance in identifying Lynch syndrome. Therefore, the EWG does not recommend the use of family history to exclude individuals with newly diagnosed cancer from the offer of genetic testing.
Costs per Lynch syndrome case detected depend on the testing strategy selected; higher costs are associated with higher sensitivity. Total program costs are highest when no preliminary tests are employed (e.g., all individuals with newly diagnosed CRC are offered DNA sequencing).
CRC is the second leading cause of cancer-related death in the United States in both men and women, with an estimated 52,000 deaths in 2007.1 About 1 in 30 CRC patients (2–4%) have Lynch syndrome.2 When other relatives are found to carry a deleterious MMR gene mutation, they are also classified as having Lynch syndrome, because they are predisposed to developing these cancers, as well. The EWG avoids the term hereditary nonpolyposis colorectal cancer (HNPCC) because it now adds confusion to the understanding of this disorder. HNPCC has been applied to families meeting only limited family history criteria and to individuals with CRC having MSI-high test results, but no vertical transmission of a MMR gene mutation.3,4
The four MMR genes of major interest are MLH1, MSH2, MSH6, and PMS2. Mutations in MLH1 and MSH2 together account for the majority of Lynch syndrome cases diagnosed; mutations in MSH6 and PMS2 are less common. The risk of CRC in individuals with Lynch syndrome is high for both a second primary CRC in the patient (estimated at 16% within 10 years), and a new cancer in a first- or second-degree family member with Lynch syndrome (about 45% for men and 35% for women by age 70).5 Changing management of both patients and relatives with the MMR gene mutation has the potential for reducing CRC-related morbidity and mortality. To better understand the utility of DNA testing strategies in reducing morbidity and mortality from Lynch syndrome, EGAPP commissioned an evidence-based review to address an overarching question regarding the following specific clinical scenario:
Does risk assessment and MMR gene mutation testing in individuals with newly diagnosed CRC lead to improved outcomes for the patient or relatives, or is it useful in medical, personal, or public health decision making?
This statement summarizes the supporting scientific evidence used by the EWG to make recommendations regarding the use of testing strategies to identify Lynch syndrome (presence of a MMR gene mutation) among newly diagnosed cases of CRC.
EGAPP is a project developed by the National Office of Public Health Genomics at the Centers for Disease Control and Prevention to support a rigorous, evidence-based process for evaluating genetic tests and other genomic applications that are in transition from research to clinical and public health practice in the United States 6 A key goal of the EWG is to develop conclusions and recommendations regarding clinical genomic applications, and to establish clear linkage to the supporting scientific evidence.7 The EWG members are nonfederal multi-disciplinary experts convened to establish methods and processes, set priorities for review topics, participate in technical expert panels for commissioned evidence reviews, and develop and publish recommendations.
EGAPP commissioned an evidence review through the Agency for Healthcare Research and Quality (AHRQ); the Tufts New England Medical Center Evidence-based Practice Center conducted the review.8 The review focused on the accuracy of diagnostic strategies for HNPCC, and the implications of testing to individuals with CRC and their families. It was anticipated that data might not be available to directly answer the overarching question. The EWG, therefore, constructed an analytic framework and key questions to address different components of evaluation (e.g., analytic and clinical validity, intermediate outcomes of interest, and clinical utility) for the purpose of providing relevant indirect evidence of efficacy. Established methods were followed in conducting this review.9 A Technical Expert Panel that included three EWG members was available to provide expert guidance during the course of the review. The final report, “Hereditary Nonpolyposis Colorectal Cancer: Accuracy of Diagnostic Strategies and Implications to Patients with Colorectal Cancer and Their Families,” is available online.8
In addition, a technical contractor with experience in evidence review collaborated with EGAPP staff and consultants to conduct a supplementary targeted evidence review5 based on EGAPP methodology.10 This supplementary review was initiated because Lynch syndrome emerged as being of more specific interest than the less well-defined clinical constellation of HNPCC, and because EWG members requested additional information to address questions dealing with impact of testing strategies on relatives.
EWG members reviewed the AHRQ evidence report, the supplementary targeted review, and key primary publications in detail, and examined other sources of information to address specific gaps in the evidence. The writers of the supplementary report and these EGAPP panel members further collaborated in constructing simple economic models to assist in analyzing the limited evidence available on clinical utility and in estimating how various testing strategies might function in practice. The final EGAPP recommendation statement regarding the use of testing strategies aimed at reducing morbidity and mortality from Lynch syndrome was formulated based on magnitude of effect, certainty of evidence, and consideration of contextual factors (e.g., severity of disorder, family considerations, and costs).
Strategies for risk assessment are defined in this review as a test or a specific series of tests offered to individuals with newly diagnosed CRC to identify those at sufficient risk for Lynch syndrome to be candidates for MMR gene testing. Based on the AHRQ evidence report, it was decided not to use the family history as an initial screening test (e.g., Amsterdam II or Bethesda criteria) because of the difficulty and costs of obtaining reliable family history and the overall poor sensitivity and specificity of this approach as a first step in identifying risk for Lynch syndrome in this clinical scenario. Possible preliminary tests include either MSI of tumor tissue that can identify the loss of MMR gene function, or IHC testing that identifies the absence of MMR gene protein in tumor tissue. Direct testing of the patient’s DNA can then be performed by sequencing to identify deleterious mutations in MMR genes, and multiplex ligation-dependent probe amplification (MLPA) to detect deletions in MMR gene exons. Testing for the BRAF V600E mutation is also being evaluated for use in patients whose IHC study indicates absence of the MLH1 protein. BRAF mutation testing is associated with methylation abnormalities of the MLH1 promoter region which are not found in association with MLH1 mutations. Individuals found with the BRAF mutation are unlikely to have Lynch syndrome and, therefore, can avoid the need for expensive MMR gene testing.
Analytic validity refers to a test’s ability to accurately and reliably measure the analyte or genotype of interest, and includes measures of analytic sensitivity and specificity, assay robustness, and quality control. Three preliminary tests (MSI, IHC, and BRAF) are relevant for Lynch syndrome, as well as diagnostic testing for mutations in specific MMR genes via sequencing, and for MMR gene deletions by MLPA. Although a comprehensive review of these tests was not performed, general information regarding these tests is summarized below.
The clinical validity of a genetic test defines how well test results correlate with the intermediate or final outcomes of interest. In this clinical scenario, the evidence for clinical validity is dispersed among studies examining MSI, IHC, BRAF and MMR gene testing, singly and in various combinations. MMR gene testing for one of the mutations of interest is the standard for defining Lynch syndrome. Thus, the EWG examined evidence comparing performance of MSI, IHC, and BRAF as preliminary tests to identify individuals who should be offered diagnostic MMR gene testing.
To determine clinical sensitivity of MSI testing, the ideal study would be to enroll individuals consecutively diagnosed with CRC from a typical population and perform MMR gene mutation testing on all, followed by MSI testing on those identified with Lynch syndrome. No such studies were found. Of 11 studies meeting inclusion criteria (examining a total of 150 patients with Lynch syndrome), only one was population based, but it was restricted to younger probands.5 The review was further complicated in that studies did not use the same markers (or the same number of markers) in the MSI panel, with some using as few as two and others as many as 11. A high proportion of mutations in the MLH1 and MSH2 genes can be associated with MSI-high results; about 89% if three or more mononucleotide markers are used. Sensitivity for MSH6 is probably lower, estimated at 77%, even with a comprehensive panel. Current practice in clinical laboratories may result in lower performance than in research laboratories. Six studies provide information regarding clinical specificity, leading to an estimate of approximately 90.2% (false positive rate of 9.8%). Two used only one mononucleotide marker (BAT26) to define MSI status and, as might be expected, both showed higher specificities (lower false positive rates) than the consensus.
The optimal study design to determine clinical sensitivity of IHC testing would be similar to that for MSI; none were identified. Nine studies met inclusion criteria (examining a total of 149 patients with Lynch syndrome).5 Sensitivity for MLH1, MSH2, and MSH6 are each estimated at 83%, based on seven studies for MLH1 and MSH2, and five studies for MSH6. Two studies were informative with respect to specificity, leading to an estimate of approximately 90% (false positive rate of 10%).
About 90% of the mutations in the BRAF gene in CRC tumors are accounted for by a transversion (1799 T>A), identified as V600E. The BRAF mutation is often present when the promoter region of the MLH1 gene is methylated (methylation is the most common cause of absent MLH1 staining). When the BRAF V600E mutation is present, a deleterious MMR gene mutation has not yet been reported. These characteristics can be useful in determining which patients with absent MLH1 staining should be offered MLH1 gene sequencing. Among the three studies with useable results, no BRAF mutations were found among 42 Lynch syndrome patients with absent MLH1 staining, whereas 68% of sporadic cancers (e.g., MLH1 absent staining, but no detectable MMR gene mutation) had the BRAF mutation.5 This reduces the number of patients needing MMR gene sequencing without reducing clinical sensitivity. Indirect evidence and gray data support this finding.
The EWG found convincing evidence that the sensitivity of MSI testing is about 89% for mutations in MLH1 and MSH2, with a lower sensitivity of about 77% for mutations in MSH6 (and PMS2). Sensitivity is higher when three or more mononucleotide markers are included in the panel. Specificity is estimated to be 90.2%, with an adequate level of evidence. There is also convincing evidence that the sensitivity of IHC testing is 83%, regardless of the underlying MMR gene mutation. Specificity is more variable, with a central estimate of 88.8% and an adequate level of evidence. Inadequate evidence is available to determine the distribution of mutations in the MMR genes, but preliminary estimates are 32% MLH1, 39% MSH2, 14% MSH6, and 14% PMS2. Adequate evidence is available to estimate sensitivity (69%) and specificity (100%) for BRAF mutation testing among newly diagnosed CRC cases with absent IHC staining for MLH1.
The clinical utility of a genetic test is the likelihood that using the test to guide management will significantly improve health-related outcomes. In this clinical scenario, the question is whether a multistep testing strategy leads to improved clinical outcomes in patients or their relatives. The EWG examined a chain of evidence10 constructed from studies that individually assessed the components of clinical utility that might provide indirect evidence for clinical utility. At the highest level, these include whether testing leads to changes in clinical management for patients or relatives, and whether such changes in clinical management result in changes to outcomes, with attention to both benefits and harms. In each of these areas EGAPP found limited but promising evidence suggesting that testing can improve outcomes.
Evaluating clinical management involves answering the following two questions: (1) are management options for patients and relatives with an MMR mutation different from those without an MMR mutation; and (2) does knowledge of MMR mutation status change management decisions?
Using the chain of evidence methodology,10 the EWG found adequate evidence that an appropriate testing strategy could lead to acceptable changes in management that can improve clinical outcomes for patients and their relatives. Although there are no randomized trials exploring whether systematic colonic surveillance (e.g., colonoscopy) is effective in reducing Lynch syndrome–related morbidity and mortality, one long-term, non-randomized controlled study from Finland followed 252 relatives at high risk of having Lynch syndrome.19 Mutation testing became available during the course of the study, and all colon cancers that developed were found in relatives who carried a mutation. Using an intention to treat analysis, 10 incident CRC cases (8%) occurred among those having colonic surveillance, whereas 26 incident CRC cases (22%) occurred among relatives without such surveillance. This represents a 62% reduction in risk for CRC and a significant reduction in CRC-associated mortality among relatives of Lynch syndrome cases. Supporting evidence was also available from a cohort study of 2788 individuals from 146 Lynch syndrome families in the Netherlands (reduction in standardized mortality ratio between subjects with (n = 897) or without (n = 1073) colonic surveillance (6.5 vs. 23.9; P < 0.001).20
In a retrospective study, 61 of 315 women with MMR gene mutations selected risk reducing surgery for endometrial cancer.21 After approximately 10 years, no endometrial cancers or ovarian cancers developed in the women with surgery, whereas a third of women who did not have surgery developed endometrial cancer, and 5.5% developed ovarian cancer.
Studies reporting psychosocial sequelae of mutation testing find that distress among mutation carriers is usually short term and that noncarriers experience significant relief.5 Very few data are available with respect to concern about employment and insurance.
Existing economic analyses that included relatives with Lynch syndrome were reviewed and found to be inadequate (e.g., variability in assumptions and initial values, no consideration of impact on relatives, no assessment of IHC as the primary screening test or refined testing strategies that involve BRAF or methylation testing).22–25 The EWG commissioned a basic economic analysis comparing selected strategies of combining MSI, IHC, BRAF, and MMR gene mutation testing for the identification of Lynch syndrome among individuals with CRC and their relatives.5 Four selected sample testing strategies were included. The outcome of interest was the cost per Lynch syndrome case detected (proband, and proband and relatives), total program costs through identification of Lynch syndrome individuals, and the associated incremental costs. Although this cost consequences analysis did not allow the EWG to recommend a specific strategy, the results were used in context with the other findings to inform its recommendation.
Research gaps were identified in four areas. Further studies in these areas could contribute substantially to refining recommendations:
National Comprehensive Cancer Network (NCCN), Clinical Practice Guidelines in Oncology™ v.2.2008.27
American Society of Clinical Oncologists (ASCO) 2006,30 Update of Recommendations for the Use of Tumor Markers in Gastrointestinal Cancer.
Major contextual issues considered by the EWG included
Disclosure: Steven Teutsch is an employee, option and stock holder in Merck & Co., Inc.
Disclaimer: This recommendation statement is a product of the independent EGAPP Working Group. Although the Centers for Disease Control and Prevention (CDC) provides support to the EGAPP Working Group, including staff support in the preparation of this document, recommendations made by the EGAPP Working Group should not be construed as official positions of the CDC or the U.S. Department of Health and Human Services.