Radiation Treatment May Slow Disease Progression for Patients with Prostate Cancer

Treatment of oligometastatic prostate cancer (OMPC) with stereotactic ablative radiotherapy (SABR) was shown to improve oncologic outcomes and may slow the disease progression in men with hormone-sensitive prostate cancers, according to a study published in JAMA Oncology.¹

The SABR treatment induced a “systemic immune response,” with the treatment being enhanced by the total consolidation of the disease via prostate-specific membrane antigen (PSMA)-targeted positron emission tomography.

“SABR is a safe and effective modality for (metastasis-directed therapy) in OMPC that improves progression-free survival compared with observation and results in a systemic adaptive immune response,” wrote the researchers. “Complete consolidation of metastatic disease detectable by molecular imaging decreases the risk of subsequent metastases, suggesting an alteration in the natural history.”

Median progression-free survival for treatment with SABR improved among the 54 men observed in the study (not reached vs 5.8 months; HR, 0.30; 95% CI, 0.11-0.81; P= .002). More, the consolidation PSMA radiotracer-avid disease was found to decrease the risk of new lesions at 6 months.

Disease progression within 6 months was observed in 7 of 36 (19%) patients treated with SABR, and 11 of 18 (61%) in the observation group. Further, the risk of new cancers at 6 months was significantly lower, with occurrence in 16% of the SABR group compared to 63% in the observation alone group.

The ORIOLE 2-arm, phase II randomized clinical trial was conducted across 3 different centers in the US. Median age was 68 years for both the men allocated to SABR treatment and the men undergoing observation.

“It has been a longstanding question, especially important now in the era of immunotherapy, whether any type of radiation, and SABR specifically, can stimulate the immune system," study lead Phuoc Tran, MD, PhD, professor of radiation oncology and molecular radiation sciences at Johns Hopkins Medicine, said in a press release.² "Our trial offers the best data to date to suggest that SABR can cause a systemic immune response."

The researchers believe these findings allow for SABR treatment to be usefully paired with other immunotherapies to treat OMPC. The researchers also think these results suggest SABR treatment may impact signals that “promote the development of micrometastases in recurrent OMPC.”

Some of the limitations to this phase II trial start with the limited sample size of the investigated population. The researchers hope for validation of their findings in a phase III trial. Further, the researchers were limited in their scope to analyze the population long-term, as many patients eventually sought SABR treatment.

“This phase II randomized clinical trial showed that among men with OMPC, those treated with SABR were significantly less likely to have disease progression than those undergoing observation alone,” wrote the researchers. “Local control for SABR-treated lesions was excellent, and the adverse effects associated with SABR were mild and did not appear to affect quality of life.”

References:

1. Phillips R, Shi WY, Deek M, et al. Outcomes of Observation vs Stereotactic Ablative Radiation for Oligometastatic Prostate Cancer. JAMA Oncol. doi:10.1001/jamaoncol.2020.0147.

2. Intense form of radiation slows disease progression in some men with prostate cancer [news release]. Published March 26, 2020. https://www.eurekalert.org/pub_releases/2020-03/jhm-ifo032320.php. Accessed March 26, 2020.