High-dose, targeted radiation can be a safe and effective option for men with oligometastatic prostate cancer, according to findings presented at the 61st Annual Meeting of the American Society for Radiation Oncology (ASTRO) in Chicago.
Results of the phase II trial determined that stereotactic ablative radiotherapy (SABR), also called stereotactic body radiation therapy (SBRT), could trigger an immune system response not thought possible in this type of cancer, said Phuoc Tran, MD, PhD, principal investigator of the trial.
“This is the first bit of evidence that I’m aware of showing that SABR can induce a systemic immune response in patients with prostate cancer,” Tran, an associate professor of radiation oncology and molecular radiation sciences at the Johns Hopkins Kimmel Cancer Center, said in a prepared statement. “Other studies have made similar observations, but these are probably the most robust, sensitive and controlled observations that SABR can excite a systemic immune response.”
In the study, known as the ORIOLE trial, the researchers randomized 54 patients whose cancer had spread to sites outside the prostate after surgery or radiation into two arms. Patients in the first arm were watched, but given no treatment for six months. Those in the second arm were treated using SABR to the metastatic sites outside of the prostate.
Results showed that men who received SABR were “significantly less likely” to have increases in their PSA levels and lived “significantly” longer without any disease progression compared to those who received no additional treatment. After six month follow up, 19% of SABR-treated patients experienced disease progression; 61% of men in the observation only arm saw their disease progress.
Additionally, more than 50% of patient in the SABR arm remained progression-free more than a year after treatment, whereas the median progression time for men in the observation-only group was 5.8 months.
“There is now accumulating evidence that SABR is effective for patients with oligometastatic disease, but there are currently no biomarkers that help us to determine who benefits most from this treatment,” said Max Diehn, MD, PhD, an associate professor of radiation oncology at Stanford University, in the same statement. “Our findings represent the first molecular marker that may predict a benefit of SABR in patients with oligometastatic disease. If additional validation of this mutational signature bears out in other cohorts, then we could potentially use it to personalize which patients with oligometastatic prostate cancer should receive SABR.”