Treatment of a microscopic model of prostate cancer with 40 kBq of 225Ac-PSMA-617 or 20 kBq of 225Ac in tandem with 17 MBq of 177Lu resulted in significantly decreased tumor growth compared with 177Lu, which was ineffective as a single agent against microscopic lesions, likely because of a mismatch of particle pathlength and lesion size. The gene discussed is FOLH1; the disease is prostate carcinoma.