After colorectal cancer surgery, patients and their care teams begin planning the next phase of care. One important question is whether there may be a risk that cancer could return—and how to use available information to guide surveillance and treatment discussions.
ctDNA is a blood-based test that looks for small fragments of DNA that may come from cancer cells. For some people with colorectal cancer, ctDNA testing can contribute to conversations about recurrence risk, surveillance, and—in selected situations—treatment planning. It is not a replacement for pathology results, imaging, laboratory studies, or clinical judgment. Instead, it is one additional piece of information that can help a patient and care team make decisions together.
In this video, you will meet Ken, a stage IV colorectal cancer survivor, and one of his oncologists, John Strickler, MD.
What you’ll hear
- Ken’s experience of being diagnosed with colon cancer after retirement
- Why he and his care team discussed ctDNA testing after surgery
- What ctDNA testing looks for in a blood sample
- How ctDNA may help inform discussions about microscopic cancer that may not appear on imaging
- Why a negative ctDNA result can be encouraging but does not mean recurrence risk is zero
- Why a positive result may prompt closer follow-up or additional evaluation
- Why ctDNA results should be considered with scans, pathology findings, other laboratory tests, symptoms, and the full clinical picture
What is ctDNA?
Circulating tumor DNA, or ctDNA, is DNA from cancer cells that can sometimes be detected in a blood sample. After a tumor is removed, a ctDNA test may look for DNA fragments that match the person’s tumor.
If ctDNA is not detected, that can be encouraging. However, it does not guarantee that cancer will not return. If ctDNA is detected, it may raise concern that cancer cells remain somewhere in the body, even if they cannot yet be seen on a scan. The result must be interpreted carefully by the oncology team, with consideration of a person’s cancer stage, pathology results, treatment history, imaging, overall health, and follow-up plan.
Why a plan matters
Dr. Strickler explains that ctDNA results are most useful when the patient and care team discuss the purpose of testing in advance. This means having a shared plan for when testing may occur, whether repeat testing is appropriate, when scans may be used, and what a positive or negative result could mean in that individual situation.
For some patients, ctDNA can provide an early molecular signal that warrants closer attention before a recurrence can be seen on standard imaging. However, early information is only useful when it is considered in the full clinical context and leads to a thoughtful next step. ctDNA should be used alongside—not instead of—imaging and routine follow-up care.
Questions to ask your care team
If you have colorectal cancer and are considering ctDNA testing after surgery, you may want to ask:
- What question would ctDNA testing help answer in my situation?
- Is ctDNA testing appropriate based on my cancer stage, pathology results, and treatment plan?
- When would the blood test be performed, and would I need repeat testing?
- What would a negative result mean for my follow-up care?
- What would a positive result mean, and what additional testing or monitoring might be recommended?
- Would ctDNA results affect decisions about chemotherapy or surveillance?
- Will I still need routine scans, blood work, and appointments if I have ctDNA testing?
- Is the test covered by insurance, and is financial assistance available if needed?
Continue Ken’s story
Click here to watch the second part of Ken’s story as he shares how ctDNA monitoring became part of his ongoing surveillance. He shares how a positive test result led to further evaluation and the identification of a small area of cancer spread to his liver, as well as how continued testing has informed conversations with his care team.
Patient information disclaimer
Ken’s story reflects one individual’s experience and may not represent the experience of every person with colorectal cancer. ctDNA testing is not appropriate for every patient and does not replace pathology, imaging, laboratory testing, clinical follow-up, or individualized recommendations from an oncology team. Patients should speak with their doctor or another qualified healthcare professional about whether ctDNA testing is appropriate for their situation.
More in this series
- Ken’s Story: Using ctDNA to Help Navigate Colorectal Cancer Follow-Up
- Mary Jo’s Story: ctDNA Monitoring, MSI-High Colorectal Cancer, and Immunotherapy
- Shawn’s Story: Using ctDNA to Help Navigate Bladder Cancer Surveillance
- Patient Perspectives: Breast Cancer and ctDNA – coming soon
This educational resource was made possible by Natera, OmniOncology, and The Personalized Medicine Foundation.
