What is ctDNA, or circulating tumor DNA, and what does it mean for your breast cancer? You may have heard of ctDNA recently in the headlines or the doctor’s office. Research has been moving at a rapid pace to better understand ctDNA, a promising new tool that is giving doctors another way to monitor cancer and help personalize treatment decisions.
Here, we walk through what ctDNA is, how it is used at different stages of breast cancer and what kinds of tests are out there now and potentially in the future.
What is ctDNA?
First, let’s consider DNA: The genetic blueprint of life. All cells in your body contain DNA. Circulating tumor DNA (ctDNA) refers to the genetic blueprint of the cancer cells in the body and that can be found in the bloodstream. So, with a blood sample, you can analyze ctDNA from tumor cells using their specific codes and corresponding genetic mutations. Circulating tumor DNA is like a fingerprint of the cancer, which can be used as a marker to track the amount of cancer lingering in the body or whether it is changing over time. ctDNA can also be used to detect mutations associated with the cancer, like ESR1 or PIK3CA mutations, which can sometimes help identify targeted treatment options or give clues about how the cancer may respond to certain therapies.
Types of ctDNA tests
There are different types of ctDNA tests, and they vary in how they are performed and what they analyze. Sometimes, ctDNA is analyzed to look for specific mutations in a person’s cancer. These tests use genomic profiling to look for common mutations that could be targeted with treatments.
Other ctDNA tests measure the amount of ctDNA in the blood as an indicator of minimal residual disease (MRD) or small amounts of cancer that remain in the body. Tumor-informed tests use a sample from your original tumor biopsy to establish the genetic fingerprint of your cancer. Blood tests can then be done to see if that fingerprint is still present and to what degree. Tissue-naïve tests, on the other hand, do not require a tumor sample and may be advantageous for those who do not have a tumor sample stored. Instead, these tests search for common mutations in the blood that can be detected in many cancers.
When is ctDNA testing used for breast cancer?
For people living with metastatic breast cancer (MBC), genomic profiling ctDNA tests are sometimes used to detect mutations in cancer cells that guide treatment. For example, certain mutations in the ESR1 tumor gene may indicate that drugs like elacestrant or imlunestrant could be effective.
For certain types of MBC, testing for tumor mutations is recommended at the time of MBC diagnosis and sometimes again if a person’s breast cancer progresses. Research is underway to determine if changes in tumor mutations detected by ctDNA can also be used before progression on scans in MBC, to help guide treatment decisions. Research is also ongoing to determine how monitoring ctDNA levels may help determine how well a treatment is working for MBC.
In early-stage breast cancer, ctDNA testing is commercially available but not yet a routine part of care. However, it has the potential to help personalize treatment further when used alongside other tools, like imaging and other clinical data. By using ctDNA to detect MRD, researchers are learning how they might be able to monitor treatment response and identify recurrence earlier than current methods allow. It may also help doctors better tailor treatment, thereby ensuring patients receive the right amount of therapy, not more or less than they need.
Currently, it is unclear what the next best steps are after a positive ctDNA test for early breast cancer. Clinical trials are underway to determine how the results from ctDNA testing can be used to make treatment decisions. Talk with your doctor about whether a clinical trial using ctDNA testing is right for you.
A promising tool with limitations
Circulating tumor DNA is changing how we can understand and track breast cancer. For some, ctDNA testing brings earlier answers and more targeted treatment. For others, it may offer peace of mind or give more information about how a tumor is behaving.
These tests are not yet standard of care for every patient, and they do have limitations. In some cases, results may be difficult to interpret or offer false reassurance. This is why ongoing research is so important – to better understand how ctDNA fits into the big picture of cancer care and so is talking with your doctor to see if it fits within your care plan and goals.
Content covered in the Know More Educational Series may be an emerging area in research or technology. Talk with your doctor about what is right for you.
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