Navigating Biomarker Testing: Frequently Asked Questions

Liquid biopsies are highly specific but not as sensitive as tissue biopsies. That means, if a biomarker appears in a liquid biopsy, the physician is pretty confident the patient has that biomarker. However, if something doesn’t show up on a liquid biopsy, it doesn’t mean it’s not there. Kind of like if you looked in your closet for a shirt and saw it, you would know it is there. But if you didn’t see it, it doesn’t mean it’s not in the closet. It could have been hidden in the back or fallen on the floor.

There are a few situations that make liquid biopsies less likely to pick up results. Liquid biopsies work by looking at DNA that has been shed into the bloodstream by cancer cells. If a patient is responding well to treatment or if there is not a lot of disease in the body, there is less circulating tumor DNA, which might mean the liquid biopsy misses something.

In general, liquid biopsies are very accurate at finding point mutations like mutations in EGFR. They are slightly less accurate when finding more complex alterations such as gene fusions lor extra copies of a gene (referred to as amplification). Liquid biopsies are not able to detect histology changes like when some patients’ lung cancers change from non-small cell to small cell after treatment. However, tests are improving rapidly.

Liquid biopsies are generally used at initial diagnosis (a tissue biopsy is usually done too) and when a patient’s cancer grows after treatment. Liquid biopsy results come back usually in a week or less, making it an important test that can provide valuable information about treatment options.

Watch this video to learn about the different types of biomarker tests. 

Patients may hear other patients and medical professionals use the phrase “full battery of genomic testing”, or something similar. There are many different genomic/biomarker tests and each one is slightly different. However, the ideal test would be next generation sequencing (NGS) that tests for the following biomarkers:

• EGFR mutations
• ALK rearrangements
• ROS1 rearrangements
• RET rearrangements
• NTRK rearrangements
• MET exon 14-skipping
• BRAF mutations
• EGFR exon 20 insertions
• KRAS G12C mutations

To round out the data, your doctor should test your tumor’s PD-L1 level, which is not included in an NGS test but provides information about whether or not you might benefit from immunotherapy.  There are other relevant markers that may provide important information to your doctor, however all of the major NGS companies and all of the NGS testing that goes on in hospitals includes the important markers.

It is important to have a trusting relationship with your doctor. If you begin to ask questions about biomarker testing and are unsatisfied with the answers, it may be time to seek a second opinion. Some of the top questions to ask your doctor are:

• When should I get biomarker testing?
• Will you review the results with me when they are available?
• Will the testing need to be repeated?
• If I am not a candidate for biomarker testing, can you tell me why?
• Should I go on any treatment before my results come back? This last one is a bit of a trick question. It is very important for patients not to start immunotherapy before the results of biomarker testing come back because it could cause problems with starting on a targeted therapy. If a patient is highly symptomatic, a doctor may choose to start the patient on chemotherapy before the test results come back.

Ideally, the patient should not have to choose the biomarker test. Hospitals adept at treating lung cancer patients either have next-generation sequencing tests (NGS) in-house or contract with an outside company. Even though in-house hospital NGS may not look for as many markers as a commercial outside company, they look for all of the relevant markers to lung cancer and both are equally reliable. If your hospital has done NGS on your lung tissue, you do not need to repeat the test with another company.  If you do find yourself in the position of deciding on a biomarker test, look for a commercial vendor that does DNA and RNA sequencing. RNA sequencing helps detect fusions (also called rearrangements) like ALK and ROS1, which can be hard to detect in DNA sequencing. Cheaper tests are not less reliable. Sometimes newer tests can cost more, but if a test has been around longer it can be offered at a cheaper rate.

Liquid biopsy results take about 5-7 days. Tissue biopsy results take about 2-4 weeks (depending on if it is done in house or needs to be sent out). Ideally, patients (particularly patients with limited or no smoking history) should not be started on immunotherapy before test results come back. If necessary, patients can start on chemotherapy.

The answer to this shows just how important it is to participate in research if you have the opportunity! It used to be that testing was only relevant for patients whose disease had spread outside the lung, or metastatic disease. But now, researchers have learned that patients who have EGFR mutations, should get a targeted therapy after surgery. Standard of care is testing for an EGFR mutation either using a single gene test or using next-generation sequencing (NGS).