Myovant's oral prostate cancer drug matches incumbent in phase 3

A phase 3 trial of Myovant Sciences’ relugolix in prostate cancer has met its primary endpoint, teeing the company up to file for FDA approval next year. 

Investigators enrolled 934 men with advanced prostate cancer and randomized two-thirds of them to take GnRH receptor antagonist relugolix. The other third received depot injections of leuprolide, the standard of care for people undergoing androgen deprivation therapy. Including the control arm set Myovant up to generate the data needed to support approvals on both sides of the Atlantic.

Myovant thinks it has the data it needs to get relugolix past regulators in the U.S. and other markets. In the relugolix arm, testosterone was suppressed to castrate levels in 96.7% of patients from week five to week 48. The FDA requires drugs to achieve such suppression in at least 90% of patients to win approval.

In key markets outside the U.S., including Europe and Japan, Myovant expects regulators to want to see evidence that relugolix is at least as good as leuprolide at suppressing testosterone. The phase 3 delivered that evidence, with the 88.8% suppression rate in the leuprolide arm low enough for the trial to show relugolix is noninferior to the incumbent product.

Myovant also gathered evidence that relugolix may be better than leuprolide in some ways. Relugolix beat leuprolide across five secondary endpoints, many of which looked at the effect of the drugs on testosterone and prostate-specific antigen over the first 15 days of the clinical trial. 

With the rate of adverse events and drug-related discontinuations coming in similar across the two arms of the trial, Myovant thinks it has the data to support a filing for FDA approval in the second quarter of 2020. Filings in Europe and Japan are set to follow after the U.S. submission.

The timeline means 2020 is shaping up to be a pivotal year for Myovant. If all goes to plan, Myovant will spend the year working through the regulatory process for relugolix in two indications, namely uterine fibroids and prostate cancer.

Approval in prostate cancer would put Myovant in a fight for market share against drugs including leuprolide, goserelin, triptorelin, histrelin and degarelix. The faster onset of action of relugolix than leuprolide is one potential differentiator of Myovant’s drug. Publication of the full phase 3 data set could reveal other differentiators—or headwinds—for relugolix, particularly in regard to just how much the two drugs suppressed testosterone levels.

Some physicians want to see the FDA judge androgen deprivation therapies on their ability to bring testosterone levels down to below 20 ng/dL, not the 50 ng/dL yardstick used in the relugolix trial, on the basis that it is associated with better outcomes. 

Shares in Myovant rose more than 60% in premarket trading following the news.