Introduction: Prostate cancer with a microsatellite instability-high or mismatch repair-deficient status is not common. Few reports of the response to pembrolizumab in metastatic castration-resistant prostate cancer in a real-world setting have been reported. This case report describes a dramatic response to pembrolizumab after initial pseudoprogression in a patient with microsatellite instability-high metastatic castration-resistant prostate cancer.
Case presentation: A 70-year-old man was administered pembrolizumab for metastatic castration-resistant prostate cancer after the genetic evaluation of lymphadenectomy revealed a microsatellite instability-high status. His general condition dramatically improved after pseudoprogression. His favorable condition has been maintained for 1 year since the final dose.
Conclusion: 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.
Keywords: microsatellite instability; pembrolizumab; prostate cancer; pseudoprogression.
© 2022 The Authors. IJU Case Reports published by John Wiley & Sons Australia, Ltd on behalf of the Japanese Urological Association.