Szmulewitz RZ, et al. - Abiraterone acetate (AA) is a standard of care for metastatic castration-resistant prostate cancer (CRPC). Researchers tested their hypothesis that low-dose AA (LOW; 250 mg with a low-fat meal) would have comparable activity to standard AA (STD; 1,000 mg fasting) in patients with CRPC. Study participants were patients with progressive CRPC from 7 institutions in the United States and Singapore. Regarding prostate-specific antigen metrics, low-dose AA (with low-fat breakfast) was shown to be non-inferior to standard dosing in these patients. Low-dose AA (with low-fat breakfast) is noninferior to standard dosing with respect to prostate-specific antigen metrics.

• This study included patients (n = 72) with progressive CRPC from seven institutions in the United States and Singapore.
• Random assignment of these patients to STD or LOW was carried out.
• Prednisone 5 mg was given to both arms twice daily.
• Monthly assessment of prostate-specific antigen (PSA) was carried out.
• Testosterone/dehydroepiandrosterone sulfate were assessed every 12 weeks with disease burden radiographic assessments.
• For drug concentrations, plasma was collected.
• The primary end point was log change in PSA, as a pharmacodynamic biomarker for efficacy, using a noninferiority design.
• Secondary end points included progression-free survival (PFS), PSA response (≥ 50% reduction), change in androgen levels, and pharmacokinetics.

• A total of 36 patients were accrued to both arms.
• A greater impact on PSA was noted at 12 weeks in the LOW arm (mean log change, -1.59) vs STD (-1.19), and noninferiority of LOW was established according to predefined criteria.
• A PSA response rate of 58% in LOW and 50% in STD was noted, in addition to the median PFS of approximately 9 months in both groups.
• In both arms, a similar decline in androgen levels was reported.
• PSA response or PFS did not differ but abiraterone concentrations were higher in STD.