"Our analyses also found a potential interaction between immune content and radiation response, suggesting that combinations of radiation therapy and immunotherapies may be a treatment option worthy of further investigation," said Dr. Zhao.

Different types of immune cells were influential in different ways, indicating a complex interaction between immune cells and tumor cells. Specifically, higher levels of active macrophages and T-cells were prognostic for worse distant metastasis-free survival (p < 0.05), while active mast cells, NK cells and dendritic cells were associated with improved distant metastasis-free survival (p < 0.05). Individual cell types were examined from the genome-wide expression data using the CIBERSORT algorithm.


PD-L1, the target of several FDA-approved checkpoint inhibitors, was not associated with outcomes in this study, but PD-L2, which interacts with PD-1 similarly to PD-L1, was associated with worse treatment outcomes. Specifically, higher levels of PD-L2 were associated with greater likelihood for disease recurrence (HR = 1.17, p = 0.013), distant metastasis (HR = 1.25, p = 0.014) and prostate cancer death (HR = 1.45, p = 0.003).

"As immune checkpoint blockers have come to market, PD-L1 has received a great deal of attention—but it does not appear to be widely expressed in prostate cancer. PD-L2, however, was much more highly expressed in these tumor samples, and it also was associated with worse outcomes. The understudied PD-L2 ligand may be the better therapeutic target for patients with localized prostate cancer," said Dr. Zhao.

"The immune landscape of prostate cancer is highly complex. We need to develop treatment approaches that account for individual tumor and patient characteristics in order to prescribe the best treatments for each individual prostate cancer patient."

The abstract, "Novel associations between the immune landscape of prostate cancer and post-operative radiation response," will be presented in detail during a news briefing and the clinical trials session at ASTRO's 59th Annual Meeting in San Diego (full details below).

ATTRIBUTION TO THE AMERICAN SOCIETY OF RADIATION ONCOLOGY (ASTRO) ANNUAL MEETING REQUESTED IN ALL COVERAGE.

Study Presentation Details

Scientific Session: Clinical Trials, Sunday, September 24, 3:15 – 4:45 p.m. Pacific time, San Diego Convention Center, Ballroom 20
News Briefing: Monday, September 25, 11:00 a.m. – 12:00 p.m. Pacific, San Diego Convention Center, room 24C, webcast: http://www.bit.do/astro17-2

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