Pembrolizumab for a patient with metastatic castration-resistant prostate cancer with microsatellite instability-high.

The rarity of microsatellite instability-high tumor in castration-resistant prostate cancer may hamper pembrolizumab administration. This potentially active agent should be considered as part of a treatment regimen for patients with microsatellite instability-high castration-resistant prostate cancer. To the best of our knowledge, this is the first report of a Japanese castration-resistant prostate cancer patient who demonstrated clinical benefit from pembrolizumab treatment.