Abiraterone acetate vs. enzalutamide: a head-to-head study in men with CRPC

Apparently a group of Japanese researchers determined a while ago that we need to know whether abiraterone acetate (Zytiga) or enzalutamide (Xtandi) is the better drug for first-line treatment of chemotherapy-naive patients with castration-resistant prostate cancer (CRPC) — whether it is metastatic or non-metastatic in type.

Izumi et al. describe the Phase III trial protocol in detail in the journal BMC Cancer — and the full text of their paper is freely available on line. Unfortunately, there may be questions about whether this is a large enough trial to show a statistically significant or a clinically meaningful difference.

Basically, the ENABLE study has or very nearly has enrolled a total of 200 chemotherapy-naive patients with CRPC and randomized them to standard daily treatment with either enzalutamide or abiraterone acetate + prednisolone. (Full study enrollment was projected by April 2017, so we are assuming that the study is now either fully enrolled or will be by the end of this year.)

The primary study endpoint is time to PSA progression (TTPP), i.e., the time from randomization into the study to a first confirmed PSA progression, as defined by criteria established by the Prostate Cancer Working Group 2 (PCWG2). The study also is examining a total of eight secondary endpoints, including overall survival (OS), radiographic progression-free survival (rPFS), time to initiation of cytotoxic chemotherapy (i.e., docetatxel or cabaxitzel therapy), and others.

From the perspective of the “average patient” (who doesn’t actually exist), it would obviously be good to know if either enzalutamide or abiraterone acteate was a significantly more effective or a significantly less toxic drug than the other in the treatment of men with CRPC. And Izumi et al. currently project that the entire study will be completed by October 2019.

The other thing that we will need to be cautious about when the results of the ENABLE trial do become available is whether the results are applicable to non-Japanese populations.

It should be noted that this study is not being funded by either of the manufacturers of the two drugs being tested.


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