8-year outcomes of enzalutamide (ENZA) versus a non-steroidal anti-androgen (NSAA) for metastatic, hormone-sensitive prostate cancer (ENZAMET; ANZUP 1304).

5090 Background: We previously reported that ENZA improved overall survival (OS) after median follow-up times of 34 and 68 months, in comparison with a NSAA, when added to testosterone suppression, with or without concurrent early docetaxel, for mHSPC. We now report outcomes after median follow-up of 98 months. Methods: Participants (pts) with mHSPC were randomly assigned (1:1) from 31MAR2014-24MAR2017 to treatment with ENZA 160 mg or NSAA, in addition to testosterone suppression. Concurrent early docetaxel was used in 45%. OS was the primary endpoint and analysed with the Kaplan-Meier method, log-rank test for p-values, and Cox regression for hazard ratios (HR). Secondary outcomes included deaths due to prostate cancer (PC) versus (vs) other causes. The numbers of pts experiencing specified adverse events (AE) of grade 3-5 are expressed per 100 person-years of study treatment exposure to account for differing treatment durations. Results: After a median follow-up of 98 months, data cut-off 30JUN2024, death was reported in 285/563 (51%) pts assigned ENZA vs 337/562 (60%) assigned NSAA. OS was longer among those assigned ENZA than NSAA (medians 95 vs 70 months; OS at 96 months 50% vs 40%; HR 0.73, 95% CI 0.63 to 0.86; p=0.0001). Clinical PFS also continued to favour ENZA over NSAA (HR 0.49; 95% CI 0.42 to 0.57; p<0.0001). PC accounted for 468 of all 622 deaths, and were less frequent among those assigned ENZA than NSAA (207 vs 261). Deaths due to other causes accounted for a total of 154 deaths, and were similarly frequent among those assigned ENZA vs NSAA (78 vs 76). Mean duration of study treatment was longer for ENZA than NSAA (58 vs 36 months). 185/562 (33%) remain on ENZA with 88% on full dose. G3-5 AE of interest were reported in the following numbers of pts per 100 years of study treatment with ENZA vs NSAA: cardiac disorder 2.2 vs 2.2, nervous system disorder 2.3 vs 2.0, fall 0.70 vs 0.24. Causes of death according to PSA at 7 months are tabulated below. Among those with PSA at 7 months ≤0.2, deaths were due to PC in 29%, and other causes in 13%. Among those with PSA at 7 months >0.2, deaths were due to PC in 60%, and other causes in 13%. Conclusions: Treatment with enzalutamide continues to confer substantial OS benefits at 8 years. These findings highlight long-term safety, toxicities, non-PC causes of death, and survival outcomes of those with and without PSA ≤0.2 at 7 months. ClinicalTrials.gov Identifier NCT02446405. Clinical trial information: NCT02446405 . Landmark analysis by PSA at 7 months ENZA (N=555) NSAA (N=549) ALL (N=1104) Deaths due to prostate cancer, PSA ≤0.2 100/375 (27%) 87/270 (32%) 187/645 (29%) Deaths due to other causes, PSA ≤0.2 54/375 (14%) 33/270 (12%) 87/645 (13%) Deaths due to prostate cancer, PSA >0.2 104/180 (58%) 170/279 (61%) 274/459 (60%) Deaths due to other causes, PSA >0.2 22/180 (12%) 39/279 (14%) 61/459 (13%)