Androgen deprivation therapy (ADT) is the current gold-standard treatment for patients with metastatic prostate cancer, although, ultimately, nearly all patients will become resistant to ADT and develop the lethal metastatic castration-resistant form of prostate cancer (mCRPC). Now, findings of a post hoc analysis of data from two phase III clinical trials confirm that the CYP17-inhibitor abiraterone is an effective treatment for mCRPC, regardless of prior exposure to other antiandrogen therapies.

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In order to investigate the effects of abiraterone, data regarding overall survival, radiographic progression-free survival (rPFS), and serum PSA response from patients with mCRPC who received ADT in either the the COU-AA-301 or COU-AA-302 trials were analysed. In these trials, patients received first-line ADT in the form of GnRH agonists, and/or orchiectomy or pure androgen receptor (AR) antagonists, followed by either abiraterone or placebo plus prednisone. On the reasons for this approach, lead author Joaquim Bellmunt explains: “These two studies provided a very large dataset with sufficiently detailed data on use and duration of prior GnRH/AR antagonists...” adding that, “this allowed for a unique opportunity to conduct a post hoc exploratory analysis of this important clinical question.”

Patients were assigned to one of four quartiles on the basis of the duration of their responses to prior endocrine therapy. Analysis of these data revealed that abiraterone plus prednisone was superior to placebo plus prednisone, as demonstrated by greater overall survival, more favourable rPFS, and improved PSA response regardless of the type or duration of the response to prior endocrine therapy. A trend toward greater overall survival, and more favourable rPFS and serum PSA outcomes was observed in patients with a greater duration of response to prior endocrine therapy; although, this suggested interaction was not deemed statistically significant.

“Our findings suggest that abiraterone produces clinical benefits regardless of the type or duration of prior exposure to endocrine therapy in patients with mCRPC,” concludes Bellmunt, adding that more research is required in order to determine the exact benefit of abiraterone in patients with mCRPC who had limited initial sensitivity to prior antiandrogen therapies.