What question did this study set out to answer?

To evaluate the efficacy of pembrolizumab in a prostate cancer patient with specific biomarker profiles.

March 6, 2026SHILAP Revista de lepidopterología0 citationsOpen Access

Complete Response to Pembrolizumab in Prostate Cancer With Microsatellite Instability–High, Deficient Mismatch Repair, Tumor Mutational Burden–High, and Programmed Death–Ligand 1 Positivity

TWTobin Wise JHJennifer Heins TST. Schieber

Key Points

To evaluate the efficacy of pembrolizumab in a prostate cancer patient with specific biomarker profiles.
Detailed patient history assessment including previous treatments.
Biomarker analysis for mismatch repair deficiency and microsatellite instability.
Administration of pembrolizumab immunotherapy.
Monitoring clinical, radiologic, and biochemical responses over time.
The patient achieved a complete clinical response after 3 months of treatment.
Radiologic and biochemical responses included undetectable prostate-specific antigen levels.
Continued response observed 8 years post-diagnosis.

Abstract

A 72-year-old man initially presented with prostate cancer and a metastatic right rib lesion. He developed rapid progression on androgen deprivation therapy in 7 months and subsequent treatment with enzalutamide in 3 months. Biomarker studies after progression to castration-resistant prostate cancer revealed deficient mismatch repair, microsatellite instability–high, tumor mutational burden of 21 mut/Mb, and programmed death–ligand 1–positive disease. Based on the results of the KEYNOTE 158 study, immunotherapy with pembrolizumab was initiated. The patient had a complete clinical, radiologic, and biochemical response with an undetectable prostate-specific antigen level within 3 months and continued pembrolizumab 8 years after diagnosis.

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