A Guiding Light for Molecular Testing

It’s clear that molecular diagnostics is a rapidly evolving field of medicine. It’s also clear that, to be of use to pathologists, recommendations for the use of those molecular diagnostics must keep pace. Colorectal cancer (CRC) is the second leading cause of cancer-related death in both North America and Europe, and results from biomarker testing can help guide clinicians and oncologists on complex targeted therapy decisions to improve patient outcomes. But is current guidance sufficient?

Four professional organizations (AMP, ASCP, CAP, and ASCO) recognized a gap and decided to collaborate on biomarker testing recommendations that addressed new discoveries in the field. Together, we convened a multidisciplinary panel of experts – pathologists, oncologists, methodologists and more – to develop the guidelines and publish them simultaneously in each of the organizations’ journals. Following the Institute of Medicine standards for guideline development, the expert panel conducted a systematic review of more than 4,000 articles in the field, evaluated the strength of the evidence, and compiled a list of guideline statements.

However, we wanted to make sure we weren’t just handing down recommendations from on high, so we included patient advocates in the development process from the start and even held a public open comment period – during which we received hundreds of responses – to ensure that everyone’s voices were heard. Those practices let us refine the guidelines to tackle issues specific to practicing pathologists and clinicians. And because we know that medical science is moving ahead in leaps and bounds, we’ve made sure to plan for regular updates, so that we can integrate new advances in molecular testing for clinical management of CRC as they happen.

The pivotal new guidelines from AMP, ASCP, CAP and ASCO address the testing of a wide range of molecular biomarkers in patients with early and advanced CRC to establish standard molecular biomarker tests, guide targeted therapy decisions, and advance personalized care. And they’re not just limited to recommendations regarding the indications to test for specific predictive or prognostic biomarker mutations; they also incorporate laboratory performance, reporting and proficiency testing of molecular assays.

Until now, we have predominantly performed molecular testing in CRC to assess the use of anti-EGFR monoclonal antibodies. Such targeted treatment requires knowledge of the mutational status of EGFR pathway genes as predictive biomarkers of disease response. And yet, prior to the new molecular testing recommendations, there was a lack of published comprehensive guidance on which gene mutations should be tested, what types of tissue samples to use, and whether the results provided predictive or prognostic information for CRC patients. To fill that gap, we developed a foundation of 21 guideline statements.

What’s in the guidelines?

Our 21 guideline statements (eight recommendations, 10 expert consensus opinions, and three “no recommendation”) were established based on evidence from a systematic literature review. The guidelines support mutational testing for predictive biomarkers – genetic molecular biomarkers that forecast response to a specific therapy or treatment regimen. At this time, the predictive biomarkers that have strong evidence for testing in CRC patients are mutations in the RAS genes – KRAS and NRAS exons 2, 3 and 4. The first recommendation in the new guideline is to test for those mutations in patients who are candidates for anti-EGFR monoclonal antibody therapies, as noted earlier.

Not all biomarkers are predictive, though; some, like the BRAF V600E mutation, provide primarily prognostic information, and it’s equally important to spot those alterations. For instance, we recommend testing for deficient DNA mismatch repair (dMMR) as it may have predictive value in some clinical settings. Although we recommend MMR testing for all CRC patients as a workup test to evaluate for possible Lynch syndrome, guidelines for its use as a predictive biomarker of response to therapy have not previously been reported. We believe it can provide prognostic information – patients with dMMR tumors tend to have improved survival rates over those with proficient tumors.

Our recommendations also cover emerging biomarkers like microsatellite instability (MSI), as well as suggesting ways to streamline molecular testing processes for improved efficiency and better overall patient outcomes.

Indeed, MSI testing appears to be on its way to prominence. Why? Recent molecular biomarker data have shown the importance of MSI testing – a marker of dMMR – in selecting patients for immunotherapy (1). It’s a brand-new indication for MSI testing in CRC, but a promising one. We know that alterations in a number of critical genes in CRC development and progression – such as dMMR and BRAF-activating mutations – can affect prognosis, as measured by several metrics of tumor progression or survival. It’s clear that markers like these have tremendous potential in clinical practice; the new guidelines tackle the question of how.

What does this mean for pathologists?

The post-genome era and the increasing emphasis on precision medicine are providing enormous amounts of new data. Promising molecular cancer biomarkers are emerging every day as potential diagnostic tools for identifying CRC patients, customizing their treatment, and forecasting its likelihood of success. But the speed at which the field is developing is a double-edged sword; it means that, every day, laboratories and regulatory agencies face the challenge of rapidly and efficiently providing new test results for the management of patients with cancer.

Laboratory testing of molecular biomarkers is a complex process. It involves selecting the right assay and the right type of specimen to test, timing the test appropriately, and minimizing turnaround time for testing results. We’ve learnt in recent years that we can effectively use a plethora of technical approaches as long as the sensitivity and specificity of the tests meet clinical needs. Earlier testing approaches focused on just one or a few testing targets, but nowadays, that isn’t always enough. The current need for multiple molecular markers from potentially minute tumor samples is leading to greater use of gene panels – for instance, targeted next generation sequencing (NGS) panels – that can assay hundreds of genes and amplicons with known mutational hotspots.

We developed our recommendations to help doctors decide which molecular tests to order for patients with cancer. To get the most out of them, pathologists and oncologists need to work collaboratively to choose the testing approaches that best meet the clinical needs of their practice settings. If that happens, I anticipate that the comprehensive scope of the new guidelines will result in a more widespread adoption of standard approaches to molecular testing – and, hopefully, enhance the treatment management and overall wellbeing of our patients.

What’s coming up next?

We’ve worked hard to establish these guidelines – but now, we need to make sure everyone knows about and understands them. To that end, we’re launching an ongoing communication and information dissemination campaign to both professionals and the public. We hope it will increase awareness and assist in the integration of guideline recommendations into pathology, laboratory, and clinical practice.

We intend to review the existing guidelines every four years – or earlier, if any new research emerges that could potentially alter our original recommendations. We’ll also continue to make additional recommendations to further streamline molecular testing processes and improve patient outcomes. Based on emerging testing technologies, I anticipate that more refined testing recommendations for specific platforms, such as NGS and liquid biopsy, will appear in future updates.

In terms of emerging clinical applications, it appears that we may soon need recommendations regarding testing to identify CRC patients who are likely to respond to immunotherapy blockade. To determine for sure what needs to be done, though, we’ll need to wait for sufficient published evidence – which means that, at the moment, it’s difficult to predict a timeline.

For some time, we’ve had an array of recommendations that cover the application of individual molecular biomarkers to CRC. What’s different about our guideline is the fact that it’s a single, comprehensive unit. It fills the need for an overarching set of recommendations that span the breadth of our current knowledge. My hope is that, as the application of these new recommendations becomes widespread, we’ll start to see better outcomes for all of our colorectal cancer patients.