4CPS-226 Efficacy of enzalutamide in abiraterone-naive patients versus abiraterone-pretreated patients in mCRPC not candidates for chemotherapy

<h3>Background and Importance</h3> Patients with prostate cancer have long survival times, specifically when the cancer is metastatic the relative survival rate at 5 years is 32%, this poses some challenges when it comes to the sequence of treatments and more specifically when the patients are not candidates for intravenous chemotherapy. Clinical practice guidelines recommend (evidence 2B) the use of enzalutamide (ENZA) after abiraterone (ABI) before the reverse order, but more published data are required to reinforce the recommendation. <h3>Aim and Objectives</h3> In this prospective work we aim to know the efficacy of ENZA in metastatic castration-resistant prostate cancer (mCRPC) in ABI-naive patients versus patients who have previously taken ABI, in order to establish whether treatment with ENZA after ABI obtains relevant clinical benefit or otherwise, alternatives such as androgen blockade with testosterone should be explored. <h3>Material and Methods</h3> Patients with mCRPC and chemotherapy naive who were prescribed ENZA as part of standard clinical practice entered one of two cohorts: 1) ABI-naive or 2) post-ABI. Primary endpoint was time to treatment failure (TTF), defined as time from treatment start to discontinuation for any reason. Secondary endpoints included time to prostate-specific antigen (PSA) progression and time to disease progression. Data were collected on patients from March 2021 to July 2024. <h3>Results</h3> A total of 62 patients were enrolled: 34 in cohort 1 and 28 in cohort 2. 20 (58,8%) patients failed treatment in the ABI-naive cohort and 21 (75%) failed in the post-ABI cohort, being the median TTF (95% CI) of 13.2 months (10.9–14.2) and 7.3 months (5.0–8.9) respectively. The median time to PSA progression (95% CI) was 16.8 months (16.2–18.8) in cohort 1 vs 15.3 months (9.3–17.1) in the other; with a median time to disease progression (95% CI) of 13.8 months (12.7–16.2) vs 8.5 months (6.9–14.1). <h3>Conclusion and Relevance</h3> Median TTF and time to disease progression with ENZA were longest in ABI-naive patients, with similar results observed for PSA control. The results of ENZA obtained in patients pre-treated with ABI can be also considered clinically relevant. <h3>References and/or Acknowledgements</h3> <h3>Conflict of Interest</h3> No conflict of interest