A small phase 2 study of abiraterone acetate and prednisone led to prostate-specific antigen (PSA) level reduction in 13% of participants with metastatic prostate cancer who did not initially respond to androgen deprivation therapy. The results were published in JAMA Oncology.1

“We set an especially high bar with our goal of reducing PSA to below 0.2, which is very low, especially for this high risk population. The trial did not meet its success criteria of 6 full responders, but we feel that with 5 full responders and evidence that many more patients also received some benefit from the drug, abiraterone acetate deserves more study in this population,” said Thomas W. Flaig, MD, from the University of Colorado Cancer Center in Aurora, in a news release.2                           

According to the paper, men who have a poor response to initial androgen deprivation therapy (ADT) treatment of metastatic prostate cancer with a PSA higher than 4.0 ng/mL at 7 months have poorer prognoses.

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Dr Flaig and colleagues sought to assess the efficacy of abiraterone acetate and prednisone in patients with metastatic prostate cancer with suboptimal response to hormonal treatment.

The study was a phase 2 single-arm study of abiraterone acetate 1000 mg daily and prednisone 5 mg twice daily in 41 men with metastatic prostate cancer who had persistently elevated PSA levels higher than 4.0 ng/mL after ADT.

The final analysis included 40 participants with a mean age of 66 years. The primary end point of a PSA level of 0.2 ng/mL or lower in 12 months was achieved in 13% (n = 5) of the participants (95% CI: 4% to 27%). A partial response of a PSA reduction between 0.2 to 4.0 ng/mL was achieved in 33% (n = 13) of participants. No PSA response was observed in 40% of participants (n = 16).

The median overall survival rate was 25.8 months and progression free survival was 7.5 months. Grade 3 adverse events were reported in 11 participants and a grade 4 adverse event was reported in 1 participant.1

“This is one of the first studies to focus on this high risk group of patients with early failure of hormone induction therapy. Seeing this level of response in patients that had previously been dubbed ‘hormone resistant’ reinforces our hope that this drug will help many kinds of patients in many settings,” Dr Flaig continued in his statement.2