Complete biochemical (prostate-specific antigen) response to sipuleucel-T with enzalutamide in castration-resistant prostate cancer: A case report with implications for future research

Objective: To describe the case of a patient with castration-resistant, metastatic prostate cancer who achieved a complete and durable biochemical response after treatment with sipuleucel-T while continuing with enzalutamide and to explore the immunologic basis for such a response. Materials and Methods: We obtained serial prostate-specific antigen (PSA) measurements and bone scans to assess the patient's response to enzalutamide followed by the addition of sipuleucel-T. Using preclinical and clinical data, we describe his response through known immunobiologic mechanisms. Results: This patient's PSA level became undetectable during treatment with enzalutamide and began to increase again after 14 months. He opted for treatment with sipuleucel-T, while continuing with the enzalutamide. This resulted in another complete PSA response 6 months after exposure to sipuleucel-T. Conclusion: Sipuleucel-T typically does not produce significant PSA reductions, and, to the best of our knowledge, only 1 previous report of a durable complete PSA response in a patient with metastatic disease has been published. The timing of this response supports an immune mechanism. The biologic rationale for the combination, coupled with the clinical result observed in our patient, provides a basis for studies of the combination of sipuleucel-T and enzalutamide.