Prognostic Value of Cycle 1 SPECT SUV _mean in Patients with Metastatic Castration-Resistant Prostate Cancer Treated with ¹⁷⁷ Lu-PSMA-617

This study aimed to determine whether SPECT SUV_mean measured after the first cycle of ¹⁷⁷Lu-PSMA-617 is associated with oncologic outcomes in patients with metastatic castration-resistant prostate cancer (mCRPC). <b>Methods:</b> This retrospective study included 192 consecutive patients with mCRPC treated with ¹⁷⁷Lu-PSMA-617 who underwent SPECT 24 h after cycle 1. Associations of total tumor SPECT SUV_mean with a decline of 50% or more from baseline in prostate-specific antigen (PSA) levels (PSA50), PSA progression-free survival (PSA-PFS), and overall survival (OS) were evaluated using logistic and Cox regression adjusted for prostate-specific membrane antigen PET SUV_mean and scan interval. <b>Results:</b> Higher SPECT SUV_mean quartiles were independently associated with greater odds of PSA50 response (odds ratios of 4.45, 10.2, and 17.1 for quartiles 2 (Q2), 3 (Q3), and 4 (Q4), respectively (<i>P</i> < 0.05 for all), longer PSA-PFS (hazard ratios of 0.52, 0.29, and 0.17 for Q2-Q4, respectively; <i>P</i> < 0.05 for all), and longer OS (hazard ratios of 1.03, 0.82, and 0.42 for Q2-Q4, respectively; <i>P</i> < 0.05 for Q4 only). <b>Conclusion:</b> SPECT SUV_mean measured after the first cycle of ¹⁷⁷Lu-PSMA-617 in patients with mCRPC was prognostic for PSA50 and PSA-PFS, independent of the prostate-specific membrane antigen PET SUV_mean, whereas its association with OS was limited and observed only in the highest quartile.