Immunotherapy with Keytruda (pembrolizumab) may be an effective way to treat some cases of advanced prostate cancer according to a preliminary study conducted at Oregon Health and Science University – Knight Cancer Institute. Findings were published in the journal Oncotarget in a paper entitled “Early evidence of anti-PD-1 activity in enzalutamide-resistant prostate cancer.” Keytruda is a monoclonal antibody that blocks the PD-1 receptor on the surface of immune T-cells, allowing them to recognize and destroy tumor cells. The FDA-approved drug has been shown to work well in melanoma and lung cancer but has so far not demonstrated much anti-tumor activity in prostate cancer.
Researchers administered Keytruda in ten (10) men with metastatic prostate cancer who had received androgen deprivation therapy or the androgen receptor antagonist Xtandi (enzalutamide) but failed to respond to it. Three of the 10 men who participated on the trial responded remarkably well to Keytruda treatment. Prostate-specific antigen (PSA) levels in their blood, an early measure of treatment response, dropped rapidly and dramatically from 46, 71, and 2,503 ng/ml respectively to less than 0.1 ng/ml. In addition, two of the three men saw their tumors shrink and reported a reduction in cancer-related pain to the point of not needing their opiate pain medication. Finally, the three patients who responded to Keytruda remained free of cancer progression at 30, 55 and 16 weeks of follow up, respectively.
It is still unclear why only three of the ten men who participated in the clinical trial responded to Keytruda while others showed no signs of clinical benefit. It is not yet possible to conclude that blocking PD-1 signaling can improve survival in men with metastatic prostate cancer, or to predict which patients will respond to treatment. More research is needed to better understand the mechanisms by which Keytruda reduces prostate cancer and which factors may influence the therapeutic effect of the drug. Additional patients have been enrolled in this clinical trial.
For a review of immunotherapy in prostate cancer, see the following link.