About ctDNA
Cancer is caused by genetic mutations, and these mutations can be detected by measuring circulating tumor DNA, or ctDNA, in the blood. Detection of ctDNA allows for personalized cancer surveillance based on an individual’s unique set of cancer mutations. Circulating tumor DNA is 150–200-base-pair fragments of DNA, which originate from cancer cells and are present in the bloodstream or other body fluids. ctDNA is different than cell-free DNA (cfDNA) which is ALL the DNA in the bloodstream including germline DNA and tumor DNA. ctDNA is the portion of cfDNA that is derived specifically from the cancer.
The Personalized Medicine Foundation and CancerConnect are pleased to provide patients and caregivers the opportunity to ask questions about the role of Circulating Tumor DNA (ctDNA) in the management of lung cancer. We have put together a panel of leading cancer experts to answer questions and publish a forum for the exchange of information.
How is ctDNA used for the management of advanced lung cancer?
ctDNA can be used to rapidly and accurately determine clinical response to immunotherapy1,2 which can identify patients with metastatic NSCLC who are less likely to attain favorable clinical outcomes. This creates an opportunity to switch or intensify their treatment based on the evidence of molecular disease progression.3,4 Moreover ctDNA detection of disease progression can help patients avoid the cost and toxicity of continuing to receive ineffective treatments.
How is ctDNA used for the management of early-stage cancers?
Across all stages of surgically removed cancer, detection of ctDNA following surgery can inform patient prognosis and help guide patient treatment. ctDNA can be detected before treatment in 24% of patients with stage I disease, 77% of patients with stage II and 87% of patients with stage III disease with high specificity and precedes clinical detection of a recurrence by 7-9 months.5 In lung cancer the most immediate application of ctDNA monitoring for minimal residual disease (MRD) for the early detection of cancer recurrence and monitoring the cancers response to treatment with immunotherapy.
Dr. John Strickler of Duke University recently conducted a webinar to explain ctDNA and entertain patient questions.
Dr. Natalie Vokes of MDACC provides an update on the emerging use of ctDNA in non-small cell lung cancer here.
About Signatera
Signatera is a custom-built ctDNA test for treatment monitoring and molecular residual disease assessment in patients diagnosed with cancer. The Signatera test is personalized and tumor-informed, providing each individual with a customized blood test tailored to fit the unique signature of clonal mutations found in that individual’s tumor. Signatera is intended to detect and quantify cancer left in the body, at levels down to a single tumor molecule in a tube of blood.
What is circulating tumor DNA (ctDNA)?
Circulating tumor DNA (ctDNA) is 150–200-base-pair fragments of DNA, which originate from cancer cells and are present in the bloodstream or other body fluids.
How is ctDNA different than cfDNA?
Cell-free DNA (cfDNA) is all the DNA in the bloodstream including germline DNA and tumor DNA. ctDNA is the portion of cfDNA that is derived specifically from the tumor.
How can ctDNA help manage cancer?
There are currently four clinical applications of ctDNA to guide precision medicine in patients with cancer:
- Detection of minimal residual disease (MRD) following surgery.
- Monitoring the treatment response in the metastatic setting.
- Identifying genomic drivers of therapeutic sensitivity and resistance.
- Guiding treatment strategies to overcome resistance to treatment.
How is ctDNA used for the management of early-stage cancers?
Across all stages of surgically removed cancer, detection of ctDNA following surgery is a strong predictor of cancer recurrence. The detection of ctDNA could lead clinicians to intensify therapy in certain situations. Conversely, the absence of ctDNA could provide an opportunity to minimize surveillance or adjuvant treatment.
How is ctDNA used for the management of metastatic cancer?
ctDNA can be used to monitor treatment response, identify genomic drivers of treatment sensitivity or resistance, or identify new therapies that could overcome genomic drivers of treatment resistance.
When should ctDNA be collected?
Both tissue and blood samples are used to build a patients individualized ctDNA test. Once the test is built, only blood samples are required for the periodic follow-up tests performed to monitor for MRD or recurrence. Since DNA assays require ctDNA shedding into the bloodstream, the performance of ctDNA assays is improved when blood is collected after—rather than during—active chemotherapy. For building the initial test, tissue should be sent as soon as it is available. The optimal time for the initial blood collection is 2-3 weeks after surgery (earlier is better)
Do you need to wait a certain amount of time, post-surgery, to have the ctDNA performed?
It is advised that blood samples used for the Signatera assay should be collected 2 weeks following any surgery.
Can a “stored” tissue sample be used to build the Signatera assay?
Yes, and this is important. The Signatera assay can be useful in the management advanced cancers and patients may not have had the assay built at the time of their original diagnosis. Tumor tissue stored as a formalin-fixed paraffin-embedded (FFPE) block or on slides can be used from the original diagnosis can be used to build the assay even when stored for several years.
What is the procedure for ordering a ctDNA test?
Currently ctDNA testing must be requested by a provider so the test can be sent to the company performing the test. Patients cannot order this test. Only a physician can order the test.
Is ctDNA different from NGS testing?
Yes “Next Generation Sequencing,” or “NGS” is a platform that allows simultaneous testing of multiple molecular targets. NGS testing can be performed on tumor tissue or blood (ctDNA).
If my doctor orders NGS testing on tumor tissue, will ctDNA testing also be performed?
Not always – ctDNA is typically a separate test and will usually not be ordered together with NGS testing unless specifically requested. Providers and hospitals use a variety of different companies to perform DNA testing. Some companies, like Natera perform both ctDNA and NGS testing, while others do not.
Does insurance pay for ctDNA testing?
Signatera is covered by Medicare for: Monitoring disease progression, recurrence, or relapse for stage IIB and higher breast cancer in both the adjuvant and surveillance settings and for monitoring of response to immunotherapy treatment.
Natera welcomes all commercial insurance plans and works with patients to ensure cost is not a barrier for testing. Please refer to our website for In-Network plans that we participate with or call your insurance company. An affordable cash pay rate is available for patients who do not wish to use insurance (exclusions apply). For questions or financial assistance, please contact Natera’s Patient Coordinators:
Phone: 650.489.9050 Fax: 650.412.1962
Email: oncologybilling@natera.com
Patient-Submitted Questions
Can you explain what “Positive Below Analytical Range” means on a Signatera test? This has happened twice and both time the values were under 1.
There is a complicated explanation for this from Natera, however this is technically a positive test meaning that cancer was detected in the sample but at a lower level of detection than can be accurately quantified. Sometimes the amount of material being measured by a test is less than the ability of the test to detect it. This can often be the case when looking for individual cells or parts of cancer cells. The Signatera test is best used serially (every 3 months) to look for residual cancer – in some situations the detection of ctDNA moves above and below the threshold of detection possible reflecting the bodies immune systems effort to eradicate the cancer.
How does your ctDNA interact with active chemo drugs – beyond the chemo’s inhibition of the cancer cells, how do they interact with the ctDNA probe measurement itself?
Chemotherapy does not directly interact with the probes. Chemotherapy suppresses the ctDNA in the bloodstream, making it harder to detect the cancer.
What is difference between ctDNA tests for early cancer detection vs MRD?
Early detection tests are similar but not identical to MRD tests. Early detection tests are typically optimized to detect the early presence of an unknown malignancy. MRD tests are designed to detect the presence of a cancer that was previously known to be present but removed. As a general rule, an early detection test is broad (can detect multiple cancers) but is not as sensitive for 1 specific cancer. MRD tests are more sensitive for 1 specific cancer, but are not designed to detect other cancers.
What is difference between tumor-naive vs. tumor-informed MRD assays. How much do we know about ct DNA as a forecasting tool?
Tumor naïve tests do not require genomic sequencing of tumor tissue. These tests rely on a standard mutation and methylation panel that is common to the cancer under study. Tumor informed tests require sequencing the patient’s tumor, and then building a custom panel to detect those tumor mutations in blood. We have no head to head studies comparing the two different approaches.
I have had nine negative Signatera tests and now a positive. What are the chances I really do have a recurrence versus a false positive?
False positives are extremely rare, but there have been reports of transient positive results that spontaneously clear. If there is any doubt, I recommend rechecking the test 4-8 weeks after the positive result to confirm. If the ctDNA result remains positive it confirms the result. Liver MRI is a great test to consider if the CT scan is clear.
How reliable is ctDNA testing during chemotherapy treatment? Should the test be performed while on chemotherapy?
ctDNA testing is less likely to be positive during chemotherapy treatment. Despite that, it can still be useful during treatment. Reduction in ctDNA is associated with favorable response to treatment and better prognosis.
Why do these tests sometimes miss cancer in the lungs/liver?
These tests rarely miss disease in the liver. MRD tests tend to miss disease in the lungs, because those metastases secrete less circulating tumor DNA into the bloodstream and tend to be slower growing overall (less cell turnover to release DNA)
Can CTDNA go up as part of pseudoprogression on immunotherapy?
No… pseudoprogression is associated with lower circulating tumor DNA levels, but worsening disease on imaging.
Connect With Others for Support and Information
CancerConnect was the first social network created for people with breast cancer. Founded by oncologists to support myeloma patients and their caregivers, over 40 million individuals have accessed CancerConnect programs since 1997. CancerConnect is used by leading cancer centers like Dana Farber, Roswell Park and The James at Ohio State to support their patients. Join the conversation, ask questions, share your experience, and learn how the best cancer centers are treating breast cancer from others. Share your experience, ask a question, or start a conversation by posting on CancerConnect.
References
- Sivapalan, L. et al. Liquid biopsy approaches to capture tumor evolution and clinical outcomes during cancer immunotherapy. J. Immunother. Cancer 11, e005924 (2023).
- Stewart, M. D. & Anagnostou, V. Liquid biopsies coming of age: biology, emerging technologies, and clinical translation—an introduction to the JITC expert opinion special review series on liquid biopsies. J. Immunother. Cancer 11, e006367 (2023).
- Anagnostou, V. et al. Immuno-oncology trial endpoints: capturing clinically meaningful activity. Clin. Cancer Res. 23, 4959–4969 (2017).
- https://www.nature.com/articles/s41591-023-02598-9
- Gale D, Heider K, Ruiz-Valdepenas A, et al. Residual ctDNA after treatment predicts early relapse in patients with early-stage nonsmall cell lung cancer. Annals of Oncology; Published online 16 March 2022. DOI: https://doi.org/10.1016/j.annonc.2022.02.007
