For many people treated for colorectal cancer, surgery is a major milestone. But even after all visible cancer has been removed, the question often remains whether every cancer cell has truly been eliminated.
Unfortunately, today’s imaging scans cannot always detect microscopic cancer cells that may still be hiding in the body. Because of this uncertainty, many patients are offered chemotherapy after surgery to reduce the risk of recurrence. While this treatment can be lifesaving for some, it also comes with side effects, and not every patient will benefit from it.
Researchers are now studying whether a simple blood test could help make these decisions more personal. A study recently published in JAMA Oncology found that circulating tumor DNA (ctDNA) may identify which patients are most likely to benefit from chemotherapy after surgery for colorectal cancer that has spread to the liver.
What is ctDNA?
Cancer cells constantly shed tiny fragments of their DNA into the bloodstream. These fragments, called circulating tumor DNA (ctDNA), can sometimes be detected even when imaging tests show no evidence of cancer.
Finding ctDNA after surgery may indicate that microscopic cancer cells remain in the body even after the visible cancer has been removed, a condition known as molecular residual disease (MRD). Although these remaining cells are too small to be seen on scans, they may eventually grow and cause the cancer to return.
Scientists believe ctDNA could serve as an early warning sign, helping doctors identify patients who are at higher risk before recurrence becomes visible.
A more personalized approach
To better understand how ctDNA could guide treatment, researchers followed 298 patients whose colorectal cancer had spread only to the liver and had been completely removed through surgery. Blood samples collected within two to ten weeks after surgery were analyzed for ctDNA, and patients were monitored over time to see whether their cancer returned and how they responded to additional treatment.
The results showed a clear pattern. Patients whose blood tests detected ctDNA after surgery were more likely to experience a recurrence than those whose tests were negative. In other words, the blood test appeared to identify patients who still had microscopic cancer cells despite successful surgery.
Who benefited from chemotherapy?
Among patients who went directly to surgery without receiving chemotherapy beforehand, those with detectable ctDNA appeared to gain the greatest benefit from chemotherapy after surgery. They remained cancer-free longer and were more likely to be alive several years later compared with similar patients who did not receive additional treatment.
For patients whose ctDNA test was negative after surgery, the picture looked different. Their long-term outcomes were already very good, and chemotherapy did not appear to provide a clear additional survival benefit.
These findings suggest that ctDNA testing could eventually help doctors answer an important question: Who truly needs chemotherapy, and who may be able to avoid it?
Interestingly, the same benefit was not seen among patients who had already received chemotherapy before surgery. Researchers believe these patients may represent a different group with more aggressive disease or tumors that respond differently to treatment, underscoring that cancer care is rarely one-size-fits-all.
Why this matters
For years, doctors have relied on factors such as tumor size, the number of tumors, and pathology reports to estimate a patient’s risk of recurrence. While these tools remain important, they cannot directly show whether cancer cells are still present after surgery.
ctDNA testing offers something different. Rather than predicting risk based on what the tumor looked like, it searches for evidence that cancer may still be present at the molecular level.
If future studies confirm these findings, ctDNA could help make treatment decisions more precise. Patients with detectable ctDNA might be encouraged to receive additional therapy, while those with negative tests may be able to avoid unnecessary chemotherapy and its side effects.
More work lies ahead
Although the results are promising, researchers caution that ctDNA-guided treatment is not yet considered standard care for everyone with colorectal liver metastases.
This study observed patients receiving routine medical care rather than randomly assigning treatments, meaning additional clinical trials are needed to confirm that using ctDNA to guide treatment decisions improves outcomes. Several studies are already underway to answer that question.
Key Takeaway
Cancer treatment is increasingly moving toward personalized medicine, where decisions are based on the biology of an individual’s disease rather than broad averages. This study adds to growing evidence that ctDNA may become an important part of that future. By detecting microscopic cancer cells that scans cannot see, a simple blood test could help identify patients who would benefit most from chemotherapy after surgery, and spare others from treatment they may not need.
While more research is needed before ctDNA-guided treatment becomes routine, these findings represent another important step toward more individualized care for people living with colorectal cancer.
Reference
Kataoka K, Ito K, Nakamura Y, et al.; CIRCULATE-Japan Group. Circulating Tumor DNA Status and Adjuvant Chemotherapy in Resected Colorectal Liver Metastases. JAMA Oncology. Published online July 3, 2026. doi:10.1001/jamaoncol.2026.2191.
