Stockholm, Sweden: A blood test that detects tumour DNA circulating in the bloodstream may help select the most effective treatment options for cancer patients whose tumours have started to spread, according to one of the largest randomised controlled trials of its kind presented at the Congress of the European Society for Radiotherapy and Oncology (ESTRO 2026) [1].
The study was led by Dr Chad Tang, Associate Professor of Radiation Oncology at The University of Texas MD Anderson Cancer Center, Houston, USA, and presented by Dr Alex D Sherry, Assistant Professor of Radiation Oncology at The Mayo Clinic, Rochester, USA. It is also published today in the Journal of Clinical Oncology [2].
The research involved a group of patients with oligometastatic cancer. This is the term used when cancer has just begun to spread beyond its origin. It is currently diagnosed by counting the number of metastases that show up on X-ray, CT or MRI scans.
Dr Sherry told the Congress: "Multiple studies have suggested that treating oligometastatic cancer with a combination of both chemotherapy and local treatments directed at the site of tumours, such as high-precision radiotherapy, may improve cancer control. But counting lesions might not be the most effective way of identifying which patients might benefit from radiotherapy."
Dr Tang said: "We wanted to investigate whether a new test that measures circulating tumour DNA - parts of the tumour that are shed into the bloodstream - would help us work out which patients would benefit the most from combining chemotherapy with radiation therapy, predict their response to therapy and give them a more accurate long-term prognosis."
The trial included 237 patients in six sub-groups (a group of patients with pancreatic cancer, one with breast cancer, one with kidney cancer, two prostate cancer groups receiving different hormone therapy schedules, and a final group of patients with any other type of cancer) who each had between one and five metastases. These patients were then randomly chosen to receive either drug therapy alone or drug therapy combined with radiation therapy.
The primary goal of the trial was to see if giving radiation therapy plus drug therapy, compared to drug therapy alone, improved cancer control, which was confirmed in the study. But the researchers were also testing whether a blood test could be used to help guide treatment.
Patients' blood was collected at the start of the trial, after three months, and again when their cancer had spread, and tested for the presence of circulating tumour DNA (ctDNA).
Dr Sherry and Dr Tang's team found that patients who had tumour DNA in their blood at the start of the trial were more likely to experience continued cancer growth and were more likely to die.
They also found that those patients who had radiation therapy directed at sites of cancer spread (alongside the drug therapy) experienced improved clearance of ctDNA.
Dr Sherry explains: "This has important implications, as patients whose ctDNA was cleared from the bloodstream had much better outcomes and survival than those that didn't. This reinforces the importance of targeted treatment such as radiotherapy when treating oligometastatic cancer."
The results also suggest that if circulating tumour DNA is found in the blood stream after therapy is given, it may be a sign that the cancer is more aggressive, that it hasn't been treated effectively, or that there are additional tumour cells not picked up on scans.
The team hope that testing for ctDNA may help determine which patients could be the best candidates for radiotherapy and may also help refine therapy by letting doctors know if and when a cancer has changed and developed resistance to current treatment.
Dr Sherry adds: "We hope that future studies will evaluate whether systemic therapy should be changed in those patients and whether ctDNA can be used to help distinguish which sites of cancer are responding to treatment versus becoming resistant."
ESTRO President, Professor Matthias Guckenberger, from University Hospital Zurich, Switzerland, who was not involved in the research said: "More and more research is showing that treating patients with a limited spread of cancer with both drug therapy and high-precision radiotherapy can improve their chances of survival. This study – one of the largest carried out in this patient group – suggests that by adding a blood test we can also monitor and target patients' radiotherapy treatment much more effectively.
"The non-invasive ctDNA marker test could support established imaging techniques, providing a more refined way of checking how patients' cancer has spread and helping doctors to determine how and when radiotherapy should be used to treat it.
"Using ctDNA as a marker could also help tailor treatment where therapy might not be working as effectively, and offer additional reassurance where treatment is successful."
