A new blood test could help personalize treatment for colon cancer

Imagine that after surgery for colorectal cancer (large intestine cancer), the doctor could find out, through a simple blood test, if there are still very small traces of the disease in your body and if you truly need chemotherapy. A recent study, presented at Digestive Disease Week 2025, suggests that this might be possible in the future.

What is it about?

The study analyzed a technology called circulating tumor DNA (ctDNA). When there is a cancerous tumor, it releases small fragments of its DNA into the blood. The ctDNA test can detect these fragments.

Why is this test important?

• Avoiding unnecessary chemotherapy: Currently, many patients with stage II or III colorectal cancer receive chemotherapy after surgery to reduce the risk of the disease returning. However, chemotherapy only helps a portion of these patients and can have unpleasant side effects. This new test could help identify which patients truly need chemotherapy and which ones could avoid this additional treatment without major risks.
• Faster and personalized decisions: The ctDNA test can provide real-time information about the cancer’s status, much faster than traditional methods, such as CT scans. This allows doctors to make treatment decisions more quickly and more tailored to each individual patient.

What did the BESPOKE study discover?

Researchers followed nearly 1800 patients with colorectal cancer (stages II-III) who underwent surgery. After surgery, these patients underwent the ctDNA test at different time intervals.

Here are the main findings:

• Patients with no signs of disease in the blood (ctDNA negative) had a better outcome: Those whose ctDNA test did not detect traces of cancer in the blood after surgery had a much lower risk of the disease returning compared to those whose test was positive. This good outcome was maintained regardless of whether they received chemotherapy or not.
• Chemotherapy primarily helped patients with signs of disease in the blood (ctDNA positive): Patients whose ctDNA test was positive (meaning traces of cancer were found in the blood) and who received chemotherapy had a higher chance of being disease-free for 2 years compared to those with a positive test who did not receive chemotherapy.
• An interesting result: Patients who had no signs of disease in the blood (ctDNA negative) and who still received chemotherapy had the best 2-year disease-free survival rates. This suggests that although the main benefits of chemotherapy were seen in ctDNA positive patients, there might be some situations where ctDNA negative patients could also benefit from chemotherapy, but this aspect requires more research.
• The study’s main conclusion: The benefits of chemotherapy after surgery were observed especially in patients who had a positive ctDNA test. This test can help guide treatment decisions and predict disease recurrence earlier than classical scanning methods.

What do experts say?

Dr. William M. Grady, a specialist in gastrointestinal cancers, praised the study, stating that ctDNA testing to detect molecular residual disease (MRD) is better at predicting disease outcome than traditional methods (such as CT scans or certain blood markers like CEA). However, he emphasized that more follow-up time for patients and more research are needed to fully understand how this test can improve long-term patient outcomes.

What does this mean for the future?

ctDNA tests are increasingly being used by doctors to assess if there are still traces of cancer after treatment. This study provides new evidence that the ctDNA test could transform the way colorectal cancer is monitored. However, more research is needed for this test to become a standard part of patient care.

In short: This study shows that a blood test (ctDNA) can help doctors better decide who needs chemotherapy after colorectal cancer surgery and who can safely avoid it, thus preventing unnecessary side effects. It is an important step towards more personalized and effective cancer treatment. Discuss with your oncologist to understand what these new findings mean for your particular situation.

Source Medscape