Curated by the CION oncology team · Medically reviewed by Dr. Owais Mohammed, MBBS, MD (General Medicine), DrNB (Medical Oncology), MRCP SCE (Medical Oncology, UK) — Medical Oncologist, CION Cancer Clinics. Last reviewed: June 2026.

The question every colon cancer patient asks after surgery

After surgery for colon cancer, one of the hardest decisions is whether to have chemotherapy to lower the risk of the cancer returning — what doctors call adjuvant chemotherapy. The difficulty is that current tools can’t tell exactly who still has a few microscopic cancer cells left behind and who is already cured. So many patients receive chemotherapy “to be safe”: some go through the side effects without truly needing it, while a few who do need more still relapse. A simple blood test is now being studied to answer this question more precisely. Here’s what the latest research shows — and, just as importantly, what it does not yet mean for patients today.

What is ctDNA, and what is “molecular residual disease”?

Tumours shed tiny fragments of their DNA into the bloodstream. These fragments are called circulating tumour DNA (ctDNA). After surgery, if a sensitive test still detects ctDNA, it suggests some cancer cells remain — a state called molecular (or minimal) residual disease (MRD) — and a higher chance of recurrence. If no ctDNA is found, the risk is lower.^[1][2] This is part of a broader move towards liquid biopsy and biomarker-guided cancer care.

What the latest trial found (DYNAMIC-III, 2025)

One of the most discussed studies at the 2025 European Society for Medical Oncology (ESMO) Congress was the DYNAMIC-III trial — an international phase 2/3 study in stage III colon cancer, published in Nature Medicine and led by Dr Jeanne Tie with Johns Hopkins and around 20 centres across Australia and Canada.^[3] Of roughly 968 patients analysed, about 72.5% had no detectable ctDNA after surgery, and they had far fewer recurrences than those who tested positive.^[3] The key findings:

• For ctDNA-negative patients, giving less chemotherapy reduced drug exposure and hospital stays — but recurrence-free survival was slightly lower than standard treatment (about 85% vs 88% at three years), narrowly missing the bar to be called “just as good.”^[3]
• For ctDNA-positive patients, more ctDNA meant higher recurrence risk — but intensifying chemotherapy did not improve outcomes.^[3]
• ctDNA that persisted after treatment signalled a markedly worse outlook.^[3]

An earlier study in stage II colon cancer (the DYNAMIC trial, published in the New England Journal of Medicine in 2022) had shown that a ctDNA-guided approach could safely reduce how many patients received chemotherapy without lowering survival.^[4]

So — can a blood test decide your chemo today?

Not on its own, yet. The research is genuinely encouraging and shows ctDNA is one of the most powerful tools we have for predicting recurrence risk and supporting honest, shared decisions between patient and doctor. But the latest results also make clear that we are not at the point of using a blood test alone to safely skip or change standard chemotherapy for most patients. Treatment decisions still rest on the full picture — the stage, the surgery and pathology findings, your overall health, and international guidelines (such as NCCN and ESMO) — with ctDNA as an increasingly useful extra input.^[5] Larger trials are underway to define exactly how to act on the result. You can read more about this shift in our overview of precision medicine in cancer.

What this means for patients in India

ctDNA / MRD testing is beginning to reach major cancer centres in India, but it is not yet a routine, standard-of-care test for colon cancer here, and access and cost vary. Tumour-informed versions also need a sample of the original tumour to be analysed first, which adds time and expense. If you or a family member has had colon cancer surgery, the practical step is to ask your oncologist whether ctDNA testing is appropriate and available in your case — and not to make treatment decisions based on a blood test alone.

Talk to a specialist

For an expert view on colon cancer treatment, recurrence risk, or a second opinion, CION offers a free first consultation and a free written second opinion across its centres in Telangana and Andhra Pradesh. To understand the disease itself, see our guide to colon cancer symptoms and types, or call 1800 202 8726.

Key takeaways

• ctDNA is tumour DNA in the blood; after surgery it can flag “molecular residual disease” and a higher chance of recurrence.
• The 2025 DYNAMIC-III trial confirmed ctDNA is a powerful predictor of recurrence in stage III colon cancer.
• Reducing chemo in ctDNA-negative patients cut side effects but narrowly missed being “as good as” standard care; intensifying chemo in ctDNA-positive patients did not help.
• A blood test cannot yet replace standard treatment decisions — it is a valuable extra input, not the whole answer.
• In India, ctDNA/MRD testing is emerging but not yet routine; discuss it with your oncologist.

Frequently asked questions

Is ctDNA the same as a routine blood test?
No. It is a specialised test that looks for tiny fragments of tumour DNA in the blood, not a standard blood count or chemistry panel.

If my ctDNA test is negative, can I skip chemotherapy?
Not automatically. A negative result is reassuring, but the latest trial showed reducing chemo on that basis narrowly missed being as effective as standard treatment. Decisions must be made with your oncologist using the full picture.^[3]

Is ctDNA testing available in India?
It is becoming available at some major centres but is not yet a routine, standard test for colon cancer, and cost and access vary. Ask your oncologist whether it applies to your situation.

Does a positive ctDNA test mean the cancer has come back?
It signals a higher risk and the possible presence of residual disease, prompting closer monitoring — but it is interpreted alongside scans and clinical findings, not on its own.

References

1. Tie J, et al. Circulating tumor DNA analysis detects minimal residual disease and predicts recurrence in patients with stage II colon cancer. Science Translational Medicine. 2016.
2. Pascual J, Turner NC, et al. ESMO recommendations on the use of circulating tumour DNA assays for patients with cancer (ESMO Precision Medicine Working Group). Annals of Oncology. 2022.
3. Tie J, et al. Circulating tumor DNA-guided adjuvant therapy in locally advanced colon cancer: the randomized phase 2/3 DYNAMIC-III trial. Nature Medicine. 2025. Trial registry ACTRN12617001566325; presented at the ESMO Congress 2025.
4. Tie J, et al. Circulating Tumor DNA Analysis Guiding Adjuvant Therapy in Stage II Colon Cancer. New England Journal of Medicine. 2022;386(24):2261–2272.
5. NCCN and ESMO Clinical Practice Guidelines for the management of colon cancer.

This article is for general information and awareness only and is not a substitute for professional medical advice, diagnosis, or treatment. Always consult a qualified oncologist about any questions regarding a medical condition. Treatment outcomes vary from person to person. Any costs mentioned are indicative and subject to change.