<b>Methods:</b> This retrospective analysis included 88 patients with metastatic castration-resistant prostate cancer from 3 U.S. institutions (University of California Los Angeles, University of California San Francisco, and Johns Hopkins) enrolled in the Expanded-Access Program who underwent baseline PSMA PET/CT before receiving <sup>177</sup>Lu-PSMA. The gene discussed is FOLH1; the disease is prostate cancer.