Blood Test Identifies Candidates for Targeted Radiotherapy in Advanced Prostate Cancer

For men with hormone-resistant oligoprogressive prostate cancer, identifying those most likely to benefit from targeted radiotherapy remains challenging due to variable treatment outcomes. New findings suggest that a blood test measuring circulating tumor DNA (ctDNA) may help predict which patients are more likely to benefit from stereotactic body radiotherapy.

Researchers at The Royal Marsden NHS Foundation Trust, The Institute of Cancer Research (ICR), London, and University College London conducted a new analysis of the TRAP trial to evaluate circulating tumor DNA (ctDNA) as a predictor of radiotherapy outcomes. The blood-based test detects fragments of genetic material released by cancer cells into the bloodstream, potentially revealing disease activity that is not visible on imaging.

The TRAP trial investigated stereotactic body radiotherapy (SBRT) in patients with hormone-resistant oligoprogressive prostate cancer, in which disease progression is limited to fewer than three sites. Patients received targeted radiotherapy to these areas while continuing hormone-based treatments, including abiraterone or enzalutamide.

Researchers analyzed blood samples collected before radiotherapy from 77 men who were followed for more than two years. Of these, 19 had detectable ctDNA, while 58 tested negative. Men without detectable ctDNA had a median progression-free survival of 7.8 months following radiotherapy, compared with three months among those with detectable ctDNA.

At six months, approximately 58% of ctDNA-negative patients remained free from disease progression, compared with 21% of ctDNA-positive patients. The association remained significant after adjusting for age, prostate-specific antigen levels, prior chemotherapy, and tumor location. These findings suggest that pretreatment ctDNA testing could help identify patients more likely to benefit from SBRT and inform future studies of personalized treatment strategies for advanced prostate cancer.

“Having a blood-based marker that aids us in determining for whom this is an appropriate approach is extremely helpful. It allows those that will benefit to continue abiraterone and enzalutamide and have SBRT alongside, whereas for others, the right approach might be to move on to a new medication for their prostate cancer,” said Dr Alison Reid, Consultant Medical Oncologist at The Royal Marsden NHS Foundation Trust and First Author of the trial.

Related Links
The Royal Marsden NHS Foundation Trust
The Institute of Cancer Research
University College London