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On May 23, 2017, the field of precision medicine achieved a major milestone with the FDA’s first ever approval of a cancer therapy based entirely on a tumor’s unique characteristics and not where the tumor developed in the body.  In other words, while therapies to date have been approved for cancers based on location, like prostate, lung, stomach, etc., this new approval is based entirely on characteristics that can be found in any solid tumor type, regardless of where they live.  Pembrolizumab (Keytruda) immunotherapy was approved for patients with solid tumors that either cannot be surgically removed or are metastatic, who have progressed on prior treatment or have no other satisfactory treatment options available, and have certain genetic defects that cause tumors to be susceptible to this class of immunotherapy.  This important approval defines a subset of prostate cancer patients that may benefit from treatment with pembrolizumab.

Pembrolizumab is a medication that activates immune cells to seek and kill tumor cells.  This class of therapies is highly effective in patients with melanoma, lung cancer and lymphoma, and is being tested in many other solid tumor types. Up until now, this class of therapy has been less effective for prostate cancer.

In the studies that led to this FDA approval, pembrolizumab was found to be effective against cancers that have genetic defects that cause extremely high levels of mutations, which can easily be identified by common genetic tests.  These included patients with 15 cancer types including prostate, colorectal, endometrial, gastrointestinal, and breast cancers.  Scientists hypothesize that pembrolizumab immunotherapy works in these patients because the immune system can more easily target tumors with higher numbers of mutations.

Prostate Cancer Foundation (PCF)-funded investigators have found that approximately 5% of advanced prostate cancer patients have these genetic defects and may therefore benefit from treatment with pembrolizumab.  This new avenue of precision medicine will enable patients with advanced prostate cancer to be screened for these defects and offered a promising new individualized treatment.

Dr. Andrea Miyahira has a PhD in cancer immunology, and is Director of Research at the Prostate Cancer Foundation.