Prostate cancer, the second leading cause of cancer-related death for men in the United States, is poorly responsive to immunotherapy. Recent clinical trials have hinted that combining immunotherapy and radiation therapy may be a powerful treatment approach for castration-resistant prostate cancer.

Austin Kirschner, MD, Ph.D., and colleagues combined radiotherapy with immune checkpoint inhibition in a castration-resistant prostate cancer mouse model. They established prostate cancer tumors in two different locations in each mouse, treated the mice with PD-1 or PD-L1-directed immunotherapy and irradiated one of the two tumors.

The combined therapy increased median survival 70-130 percent compared to immunotherapy alone. The investigators also observed an abscopal treatment effect: the unirradiated tumor responded similarly to the irradiated tumor in the same mouse, suggesting that combination treatment may be effective for widespread metastatic disease.

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