Dramatic response to pembrolizumab after pseudoprogression in a patient with advanced metastatic castration-resistant prostate cancer.

We experienced a case of dramatic response to pembrolizumab after pseudoprogression in a patient with advanced metastatic castration-resistant prostate cancer. In patients with metastatic castration-resistant prostate cancer and the microsatellite instability-high/mismatch repair-deficient phenotype, a few months follow-up is necessary to evaluate the efficacy of pembrolizumab.