The ORIOLE trial, only the second randomized clinical trial to report findings on SABR for oligometastatic prostate cancer, has also shed light on what happens to the immune system when the disease is treated with high-dose radiation therapy.
The research team looked at blood cells sampled before radiation therapy and 90 days after treatment; they found “significant, measurable changes” in the T cells of patients on the SABR arm, but no change in the T cells of those in the observation arm. “The magnitude of change in the immune system response was similar to what you see after a vaccination” said Dr. Phillips, suggesting that radiation may spark the immune system to more aggressively fight the cancer.
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“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,” said Phuoc Tran, MD, PhD, principal investigator of the trial and an associate professor of radiation oncology and molecular radiation sciences at the Johns Hopkins Kimmel Cancer Center. “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.”
“Cancer of the prostate is a tumor that does not typically incite a response from the immune system, so seeing this response is exciting,” he added. “There is still much work to be done to understand how radiation and the immune system interact.”
Using a sophisticated type of imaging largely accessible only to research institutions, the study also shed light on how high-dose radiation therapy may alter the course of prostate cancer spread or metastasis.
Typically, metastatic prostate cancer lesions are detected using conventional imaging technologies such as bone scans, MRIs and/or CT scans. The ORIOLE trial used these conventional imaging techniques to identify patients eligible for their study (eligibility was based upon the detection of one to three metastatic lesions), but also made use of a more sensitive, advanced imaging technology known as a prostate-specific membrane antigen (PSMA) PET scan. This scan detects proteins that are overexpressed in prostate cancer and can reveal the presence of otherwise undetectable tumor growth.
Patients randomized to the SABR arm (n=36) received radiation to all lesions detected by conventional imaging. However, they also underwent PSMA PET scans prior to and 180 days after treatment. The results of those scans were not made available to the physicians developing their treatment plans; they were used only for further analysis and comparison of cancer growth.
