Effects of [¹⁷⁷Lu] Lu-PSMA-617 on overall survival in TheraP versus VISION randomized trials: An exploratory analysis.

5045 Background: Observed effects on overall survival (OS) differed in the first two randomized trials (RCTs) of [ 177 Lu] Lu-PSMA-617 (LuPSMA) in metastatic, castration-resistant prostate cancer. TheraP randomized participants to LuPSMA or Cabazitaxel (CBZ). In TheraP, the CBZ group (n = 101) included 20 participants who crossed over to LuPSMA, and the LuPSMA group (n = 99) included 32 who crossed over to CBZ. VISION randomized participants to treatment with or without LuPSMA, plus physicians’ choice among protocol-defined treatments, excluding CBZ. Thirty-eight percent of control group participants in VISION had received CBZ prior to randomization. This study investigated explanations for differences in these RCTs in the observed effects of LuPSMA on OS. Methods: Individual participant data (IPD) on survival time from VISION was extracted from published survival curves for comparison with IPD from TheraP. Rank-preserving structural failure time (RPSFT) and inverse probability of censoring weighting (IPCW) were used in TheraP to estimate treatment effects on OS in counterfactual analyses assuming crossover had not occurred in either group, or in both groups. Results: OS was longer in the comparator group of TheraP than the comparator group of VISION (HR: 0.57, 95% CI 0.43 - 0.75) while OS was similar in the LuPSMA groups of VISION and TheraP (HR: 0.92, 95% CI 0.70 - 1.19). No significant differences in OS between the LuPSMA and CBZ groups of TheraP were apparent using counterfactual analyses assuming crossovers had not occurred (No crossover from CBZ: RPSFT HR 0.97, 95% CI 0.62 –1.52, IPCW HR 0.92, 95% CI 0.65-1.32; No crossover from LuPSMA: RPSFT HR 0.97, 95% CI 0.60–1.58, IPCW HR 0.82, 95% CI 0.55–1.24; No crossover from LuPSMA or CBZ: RPSFT HR 0.97, 95% CI 0.53-1.74, IPCW HR 0.82, 95% CI 0.53–1.27). Conclusions: The difference in observed effects of LuPSMA on overall survival in TheraP and VISION are better explained by the use of different comparator treatments in their control groups than by crossovers in TheraP from Cabazitaxel to LuPSMA, or LuPMSA to Cabazitaxel. Clinical trial information: NCT03392428 , NCT03511664 .