Predictors of overall and disease-free survival in metastatic castration-resistant prostate cancer patients receiving 225Ac-PSMA-617 radioligand therapy

Metastatic prostate carcinoma overexpresses prostate-specific membrane antigen (PSMA), making this antigen a suitable target for radioligand therapy of the disease. Here we report on our experience with a series of 73 castration-resistant prostate carcinoma patients treated with 225Ac-PSMA-617, identifying variables predictive for overall survival (OS) and progression-free survival (PFS) after 225Ac-PSMA-617 treatment. METHODS : 225Ac-PSMA-617 was administered to patients who had metastatic castration-resistant prostate carcinoma and who had exhausted available therapy options for their disease. Full blood count, glomerular filtration rate, and liver function test were obtained at baseline and on follow-up for evaluation of toxicity. 68Ga-PSMA PET/CT was obtained at baseline, before every treatment cycle, and on follow-up for selection of patients for treatment, to determine the activity of the treatment agent to be administered, and for response assessment. Serial prostatespecific antigen (PSA) was obtained for PSA response assessment. RESULTS : Seventy-three men (mean age, 69 y; range, 45–85 y) with metastatic castration-resistant prostate carcinoma were treated with 210 cycles of 225Ac-PSMA-617. In 70% of patients, a PSA decline of greater than or equal to 50% was obtained; 82% of patients had any PSA decline. In 29% of patients, all lesions on 68Ga- PSMA PET resolved in response to treatment. During follow-up, 23 patients experienced disease progression, whereas 13 patients died from their disease. The estimated median PFS and OS were 15.2 mo (95% CI, 13.1–17.4) and 18 mo (95% CI, 16.2–19.9), respectively. In univariate analyses, factors such as baseline PSA, any PSA decline, PSA decline of greater than or equal to 50%, prior chemotherapy, prior radiation therapy, and baseline hemoglobin seen in 5 patients with baseline renal impairment. CONCLUSION : In this study, a PSA decline of greater than or equal to 50% after treatment with 225Ac-PSMA-617 was proven by multivariate analyses to be significantly associated with OS and PFS. Furthermore, previous 177Lu-PSMA treatment was negatively associated with PFS in both univariate and multivariate analyses.http://jnm.snmjournals.orgam2020Nuclear Medicin