Analytic validity
: The accuracy and reliability of the tests in detecting the genetic changes of interest.
Based on evidence reviews, the EGAPP Working Group reported that overall the analytic validity of the tests was high although there were gaps in research on analytic validity and proficiency testing, as described below
[1],
[2],
[3]:
- MMR: DNA sequencing of 4 MMR genes (MLH1, MSH2, MSH6, and PMS2) is the practice standard, but actual performance is difficult to estimate, and it is not known if laboratory proficiency testing will be an adequate validity measure. [1],[2],[3].
- MSI: Testing is offered by many laboratories that participate in proficiency testing programs, and performance in such testing programs is high so adherence to best practices may provide valid testing [1],[2],[3].
- IHC: IHC proficiency testing is offered for other proteins, but not specifically for MMR gene proteins (1-3, 19)[1],[2],[3],[12].
- BRAF: Given that this test is to identify a single mutation and proficiency testing for some other single mutations has been high, analytic validity is likely to be high [1],[2],[3].
Clinical validity: The accuracy and reliability of the test in identifying patients with the disorder.
Based on the evidence reviews, the EGAPP working group reported that there was adequate evidence of clinical validity for the preliminary tests, although evidence varied and research gaps were identified on which tests and which combinations perform best and on the use of family history with tests, as described below
[1],
[2],
[3].
- MMR: DNA sequencing of 4 MMR genes (MLH1, MSH2, MSH6, and PMS2) is the current standard for diagnosing patients with Lynch syndrome, although research may identify additional MMR genes. Lifetime risk of colorectal cancer among individuals with Lynch syndrome is approximately 20 to 65% [1],[2],[3],[7],[8].
- MSI: Studies enrolling a total of 150 patients with Lynch syndrome and using a variety of MSI methods found that high MSI score test results were adequately sensitive and specific in identifying individuals who had tested positive for some MMR genes [1],[2],[3].
- IHC: Studies with a total of 149 patients found that IHC testing was adequately sensitive and specific in identifying individuals who had tested positive for some MMR genes [1],[2],[3].
- BRAF: Multiple studies have found BRAF mutation testing to be highly sensitive in identifying CRC tumor tissue abnormal for the MLH1 protein due to somatic changes. Thus, it is a highly effective test for ruling out the presence of Lynch Syndrome [1],[2],[3].
Research has shown that concordance between IHC and MSI test results varies
[12],
[13].
The EGAPP Working Group found insufficient evidence to recommend any one of the screening-diagnostic testing combinations or sequences over the others
[1],
[2],
[3], and there appears to be no consensus among practitioners on a best practice.
Clinical utility:The possibility that implementing a screening/testing and intervention program for Lynch Syndrome will lead to improved health.
Based on the evidence reviews, the EGAPP working group reported that there was adequate evidence from research that more than about 90% of relatives of patients with Lynch would consent to genetic testing and that more than half of those who were identified as having Lynch syndrome began screening with colonoscopy, beginning at age 20-25. A single study of relatives at high risk provides evidence that screening colonoscopy results in an approximately 60% reduction in the incidence of colorectal cancer. Harms appeared to be minimal in comparison with benefits. However, additional research was needed on the overall strategy and on each step from offering genetic testing to patients through studying the long term health benefits to relatives. Additional cost-benefit analyses are also needed. Screening or prophylactic surgery for prevention of other Lynch syndrome associated cancers (particularly endometrial) has not been fully assessed for utility
[1],
[2],
[3].
The EGAPP Working Group found insufficient evidence of benefit to CRC patient from modification of clinical management options based on testing for Lynch
[1],
[2],
[3]. The American College of Gastroenterology found moderate quality evidence for their recommendation that colorectal cancer patients with Lynch syndrome undergo colonoscopy every 2 years beginning at age 20-25 and then annually after age 40
[9].
A cost-effectiveness analysis has reported that a testing strategy using IHC as the preliminary test for individuals newly diagnosed with colorectal cancer has an incremental cost-effectiveness ratio of < $25,000 per life-year saved compared to no testing for a Lynch syndrome
[14].
Some researchers, practitioners, and members of the public have raised questions about how best to implement testing beyond research settings, how feasible it is, and how potential harms from implementation might be addressed
[15],
[16],
[17]. These questions raise issues about the clinical utility and cost effectiveness of testing in common practice.
Research is continuing on the potential utility of screening CRC patients for Lynch syndrome to assist in treatment decisions
[18],
[19].
Contextual issues: Including clinical alternatives to genetic testing, practice, ethical, legal, social issues.
The EGAPP Working Group, based on the evidence reviews, found that methods using family history, either the Amsterdam or Bethesda criteria, to identify patients with Lynch syndrome produced inconsistent results and identified a lower percentage of patients with Lynch syndrome than did tumor-based screening protocols. They also recommended informed consent for preliminary testing of patients, noted that studies suggest adverse psychosocial outcomes should be minimal, and stated that resource requirements appeared to be justified by willingness of relatives to participate and health benefits for relatives
[1],
[2],
[3].
A report suggests that more research is needed on psychosocial issues because of evidence that some subgroups are more vulnerable to testing-related stress
[20].
Lynch syndrome is associated with increased risk of a number of other cancers, including cancers of the endometrium, stomach, small intestine, bladder, brain, kidney, and biliary tract, and individuals diagnosed with Lynch syndrome may be monitored by their clinicians for those cancers as well (2-3).
The Amsterdam criteria may be used to screen individuals for presnce of Lynch syndrome based on their family history of Lynch syndrome-asociated cancers (3). The revised Amsterdam criteria include the following: at least 3 relatives with Lynch-associated cancer, one should be a 1st degree relative of the other two, at least 2 generations with Lynch-associated cancers, at least 1 diagnosed before age 50, excluding familial adenomatous polyposis, and with tumors verified by pathologic examination (3). The Bethesda criteria may be used to identify patients with colorectal cancer who could benefit from genetic testing for MMR gene mutations (3). The revised Bethesda criteria include the following: colorectal cancer diagnosed in a patient younger than age 50, presence of synchronous, metachronous, colorectal or other Lynch-associated cancers regardless of age, colorectal cancer with the MSI-H-like histology diagnosed in a patient age less than 60, colorectal cancer diagnosed in a pateint with one or more 1st degree relatives with Lynch syndrome-related tumor -- with one of the cancers being diagnosed under age 50, or colorectal cancer in a patient with two or more 1st or 2nd degree relatiaves with Lynch syndrome-associated cancers regardless of age.
Given the variety of screening approaches, including scoring of histopathological characteristics, family history criteria, and inconsistencies in the recommendations from various groups, practicing clinicians face multiple options for Lynch syndrome screening. At present, there is limited published research on how to effectively implement testing in routine clinical practice and on the benefits and costs of implementation
[15],
[16],
[17],
[21].
