Oral advanced prostate cancer agent shows safety, efficacy

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Myovant Sciences recently announced positive phase III trial results for its once-daily oral small molecule gonadotropin-releasing hormone (GnRH) antagonist relugolix, for the treatment of advanced prostate cancer.

If the FDA approves relugolix, it would be the first oral androgen deprivation therapy option for men with advanced prostate cancer, according to Neal Shore, MD, of the Carolina Urologic Research Center, Myrtle Beach, SC and steering committee member of the phase III HERO relugolix trial.

Dr. Shore was among the researchers to perform two successful phase II trials on oral relugolix for advanced prostate cancer.

“The first phase II trial compared oral relugolix once a day in comparison to 3 months treatment with a luteinizing hormone-releasing hormone (LHRH) agonist preparation for patients with advanced prostate cancer. The endpoints for that study were testosterone suppression, PSA declines, and numerous secondary endpoints,” Dr. Shore said. “The second phase II study was oral relugolix versus monthly degarelix for patients receiving radiation therapy who had intermediate-risk prostate cancer.”

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Based on the success of the two phase II studies, Dr. Shore and colleagues designed the phase III HERO trial protocol studying 934 men with advanced prostate cancer with metastatic disease, biochemical relapse, or patients with high-risk, locally advanced disease. Researchers randomized patients to either relugolix once-per-day pill or 3 months LHRH agonist therapy (leuprolide acetate).

The primary efficacy endpoint of the study was the ability of relugolix to achieve and maintain testosterone suppression to castrate levels, defined as testosterone suppression of less than or equal to 50 ng/dL from week 5 through 48 weeks. For the study to be successful, the lower bound of the 95% confidence interval of the response rate had to be at least 90%, according to Myovant.

“Essentially, the trial met its primary endpoint of noninferiority. With this hurdle passed, we were allowed to test for superiority and relugolix also achieved response rates for sustained testosterone suppression that achieved superiority over those in the LHRH agonist arm,” Dr. Shore said.

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