A phase II study reported in the Journal of Clinical Oncology by Traina et al showed activity of the androgen receptor inhibitor enzalutamide (Xtandi) in triple-negative breast cancer expressing the androgen receptor (AR).
The study involved 118 patients from 45 sites in seven countries with nuclear AR staining > 0%, including an evaluable subgroup of 78 patients with tumors expressing ≥ 10% nuclear AR. Patients received enzalutamide 160 mg once daily until disease progression. The median number of prior therapies for advanced disease was one in both the intent-to-treat population and in the evaluable subgroup. The primary endpoint was clinical benefit rate (complete or partial response or stable disease) at 16 weeks.
Clinical Benefit Rate
Among all patients, median duration of treatment was 8.1 weeks. The clinical benefit rate at 16 weeks was 25% in the intent-to-treat population and 33% in the evaluable subgroup, including one complete and five partial responses in the evaluable subgroup. Median progression-free survival was 2.9 months (95% confidence interval [CI] = 1.9–3.7 months) and 3.3 months (95% CI = 1.9–4.1 months), and median overall survival was 12.7 months (95% CI = 8.5 months–not reached) and 17.6 months (95% CI = 11.6 months–not reached). An updated overall survival analysis after an additional 18 months of follow-up (data cutoff in March 2017) showed median durations of 12.7 months (95% CI = 8.5–16.5 months) and 16.5 months (95% CI = 12.7–20.0 months).
Fatigue (3.4%) was the only treatment-related grade ≥ 3 adverse event occurring in > 2% of patients. Serious adverse events were reported in 25%. Adverse events led to discontinuation of treatment in eight patients (7%).
The investigators concluded, “Enzalutamide demonstrated clinical activity and was well tolerated in patients with advanced AR-positive [triple-negative breast cancer]. Adverse events related to enzalutamide were consistent with its known safety profile. This study supports additional development of enzalutamide in advanced [triple-negative breast cancer].”
The study was supported by the National Cancer Institute; Medivation, a Pfizer company; and Astellas Pharma.
The content in this post has not been reviewed by the American Society of Clinical Oncology, Inc. (ASCO®) and does not necessarily reflect the ideas and opinions of ASCO®.