Efficacy of Therapies After Galeterone in Patients With Castration-resistant Prostate Cancer

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Abstract

Background

Galeterone is a multi-targeted agent with activity as a CYP17 inhibitor, androgen receptor antagonist, and also causes androgen receptor degradation. It has shown meaningful anti-tumor activity with a well-tolerated safety profile in patients with castration-resistant prostate cancer (CRPC) in phase I and II studies; however, the efficacy of currently approved CRPC therapies after treatment with galeterone is unknown. In this study, we evaluate prostate specific antigen (PSA) response of non-protocol therapies following galeterone in a subset of patients treated on the Androgen Receptor Modulation Optimized for Response (ARMOR) 2 study.

Patients and Methods

Patients who received any subsequent treatment were included. PSA response and treatment duration were summarized by line and type of subsequent therapy.

Results

Overall, 27 of 40 patients received ≥ 1 post-galeterone treatment, of whom 18 (67%) discontinued galeterone for progression, 14 (52%) received ≥ 2 treatments, and 6 (22%) received ≥ 3 treatments. PSA changed by a median of −36%, −35%, and +60% in patients receiving first-line, second-line, and third-line therapy, respectively. Overall, 18 (67%) received subsequent enzalutamide, 12 (44%) received docetaxel, 9 (33%) received abiraterone, and 5 (19%) received cabazitaxel. PSA changed by a median of −27%, −34%, −39%, and 17% for patients receiving subsequent enzalutamide, docetaxel, abiraterone, and cabazitaxel, respectively, at any line.

Conclusion

We demonstrate that CRPC therapies exhibit differential anti-tumor activity following galeterone. In this small cohort, abiraterone demonstrates the highest PSA response post-galeterone, whereas enzalutamide and chemotherapy have more modest activity. Larger clinical studies are warranted to fully evaluate the efficacy and safety of second-generation hormonal agents and chemotherapy post-galeterone. Predictive biomarkers will be critical to optimizing patient selection for sequential therapies.

Micro-Abstract

We evaluated the prostate-specific antigen (PSA) responses to subsequent therapy in patients previously treated with galeterone. Twenty-seven patients were included in the analysis. Modest PSA responses were seen in patients receiving first-line and second-line subsequent therapies. The response to abiraterone was comparable with historic PSA response rates in patients with no prior exposure to second-generation hormonal therapy or chemotherapy.

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