Short-term Prostate-specific Antigen Pseudoregression Following [177Lu]–Prostate-specific Membrane Antigen Therapy

A 74-year-old man with metastatic castration-resistant prostate cancer underwent 2 cycles of [ 177 Lu]Lu-prostate-specific membrane antigen (PSMA) therapy. Despite declining prostate-specific antigen (PSA) levels and pain relief throughout the first 4 months of [ 177 Lu]Lu-PSMA therapy, follow-up [ 68 Ga]Ga-PSMA PET/CT revealed progressive skeletal involvement. A bone marrow biopsy confirmed fulminant metastatic castration-resistant prostate cancer infiltration. This case exemplifies PSA pseudoregression, where PSA suggests disease control while imaging shows progression. The patient's condition deteriorated, leading to intensive care admission and death.