In a clinical trial of 237 cancer patients, researchers at MD Anderson Cancer Center and Mayo Clinic have identified a simple blood test that could transform how doctors treat tumors that have begun to spread, potentially offering patients a more personalized path forward.
The study, led by Dr. Chad Tang at The University of Texas MD Anderson Cancer Center in Houston and presented by Dr. Alex D Sherry at Mayo Clinic in Rochester, enrolled patients with oligometastatic cancer—the early stage when tumors have just begun to spread beyond their original site but remain limited in number. These patients each had between one and five metastases, and researchers wanted to understand whether measuring circulating tumor DNA (ctDNA), fragments of cancer that shed into the bloodstream, could help guide which patients would benefit most from combining chemotherapy with targeted radiation therapy.
The trial included patients across six groups: pancreatic cancer, breast cancer, kidney cancer, two separate prostate cancer cohorts with different hormone therapy schedules, and a final group with any other cancer type. Half received chemotherapy alone, while the other half received chemotherapy combined with high-precision radiation therapy directed at tumor sites. The researchers collected blood samples at the beginning of the trial, again after three months, and once more when cancer had progressed, testing each sample for the presence of ctDNA.
The findings revealed something striking: patients who had circulating tumor DNA detectable in their blood at the start of the trial were significantly more likely to experience continued cancer growth and higher mortality rates. More importantly, those who received radiation therapy alongside their chemotherapy showed improved clearance of ctDNA from their bloodstream, and these patients experienced much better survival outcomes than those whose ctDNA remained present after treatment.
"This has important implications, as patients whose ctDNA was cleared from the bloodstream had much better outcomes and survival than those that didn't," Dr. Sherry explained. The discovery suggests that this blood test could help oncologists identify which patients are best suited for radiotherapy and predict how well they'll respond to treatment—information that currently cannot be determined by counting visible tumors on imaging scans alone.
The research also illuminated what lingering ctDNA might signal. When tumor DNA persists in the bloodstream after therapy, it may indicate that cancer is more aggressive than imaging suggests, that it hasn't been effectively treated, or that additional tumor cells remain undetected by CT, MRI, or X-ray scans. This insight could prompt doctors to adjust therapy or explore why a patient's cancer is resistant to current treatment approaches.
Dr. Tang noted that the team hopes these findings will lead to future studies evaluating whether patients with persistent ctDNA might benefit from switching to different systemic therapies, and whether this blood test could help distinguish which tumor sites are responding to treatment versus becoming resistant. The work, presented at the Congress of the European Society for Radiotherapy and Oncology and published in the Journal of Clinical Oncology, represents one of the largest randomized controlled trials of its kind to examine ctDNA as a treatment guide.
As precision medicine increasingly shapes cancer care, this blood test offers an accessible, scalable tool that could help thousands of patients receive the most effective treatment for their specific tumor biology—moving oncology closer to a future where every treatment decision is informed by the biology of the cancer itself.