A major international study has found that a simple blood test may help doctors decide which patients with stage 3 colon cancer need chemotherapy and which patients can safely avoid it.
This breakthrough could improve quality of life for many people while making cancer treatment more personal and precise.
The study, led by the Walter and Eliza Hall Institute of Medical Research (WEHI) in Australia, involved more than 1,000 patients from Australia, New Zealand, and Canada. All patients had undergone surgery to remove their primary colon cancer and had blood drawn about six weeks later.
The findings were presented at the European Society of Medical Oncology (ESMO) Congress in Germany and published in *Nature Medicine*.
The test works by checking the blood for circulating tumour DNA (ctDNA), which are tiny fragments of cancer DNA left behind in the bloodstream. If ctDNA is found after surgery, it may mean that some cancer cells are still in the body. If no ctDNA is found, the patient is considered low risk for cancer returning.
Professor Jeanne Tie, who led the DYNAMIC-III clinical trial, said this test can help doctors make smarter decisions about chemotherapy. “Right now, we treat most stage 3 colon cancer patients the same way, but this blood test shows us who really needs full chemotherapy and who doesn’t,” she said.
Patients in the study were randomly placed into two groups. One group received the usual standard chemotherapy. The other group had their treatment guided by the ctDNA test results. If ctDNA was not detected, they received a lighter chemotherapy plan or none at all. If ctDNA was found, they were given the standard treatment.
The results were impressive. About 87% of low-risk patients (those with no ctDNA) remained cancer-free three years after surgery.
These patients were able to avoid full chemotherapy, which often causes serious side effects like nerve damage and frequent hospital visits. Professor Tie said this helped patients enjoy better quality of life while still effectively treating their cancer.
On the other hand, patients with ctDNA still present after surgery had a much higher risk of the cancer coming back.
Only around half of these patients remained cancer-free after three years. Worse, even if they were given stronger chemotherapy, their results didn’t improve much. This means doctors may need to explore new treatment options for this high-risk group.
The study was carried out in partnership with the Canadian Cancer Trials Group (CCTG), the Australasian Gastro-Intestinal Trials Group (AGITG), and the Peter MacCallum Cancer Centre.
Dr. Jonathan Loree from Canada, one of the study leaders, said, “This research gives us the best proof so far that this blood test can guide colon cancer treatment. It’s a big step toward using it in regular clinical care.”
This new approach could save many patients from going through unnecessary chemotherapy, reducing side effects and improving recovery.
At the same time, it helps doctors identify which patients truly need more aggressive treatment. By making cancer treatment more personalized, this simple blood test could make a big difference in the lives of thousands of people.
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The study is published in Nature Medicine.
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