Enzalutamide Long-Term Safety and Efficacy in Hormone-Naïve Prostate Cancer
Enzalutamide is approved for the treatment of patients with metastatic castrate-resistant prostate cancer post-docetaxel. In an open-label phase 2 study in patients with hormone-naïve prostate cancer (HNPC), enzalutamide monotherapy resulted in a high prostate-specific antigen (PSA) response rate, stable bone mineral density (BMD), and improved quality of life (QOL) after 6 and 12 months of treatment, even in patients with metastatic disease at baseline (Tombal B, et al. Lancet Oncol. 2014;15:592-600). At ESMO 2014, Tombal and colleagues reported 2-year data from this study (Tombal B, et al. ESMO 2014: Abstract 766PD).
In this study, 67 patients with HNPC and noncastrate levels of testosterone (?730 ng/dL) received enzalutamide 160 mg daily until disease progression or unacceptable toxicity. At baseline, 39% of the patients had metastatic disease. At 2 years, 45 patients continue with enzalutamide therapy, and 100% of them had a ?80% decline in PSA level. Of the 26 patients with metastases at baseline, 50% had a complete response and 15% had a partial response at 2 years. QOL data from the EORTC-QLQ C30 trial showed maintenance of global health status through 2 years, although clinically meaningful deteriorations were reported on the fatigue and the role-functioning scales. The most common treatment-related adverse events reported over the 2-year treatment span were gynecomastia, fatigue, nipple pain, and hot flush. Total body BMD and lean body mass were only slightly decreased at 2 years (-0.39% and -5.27%, respectively).
Tombal and colleagues concluded that enzalutamide monotherapy is associated with significant long-term reductions in PSA levels and a good tumor response in men with HNPC, without adversely affecting total body BMD or global health status.