Can oral relugolix be used as androgen-deprivation therapy in advanced prostate cancer?

The study looked at whether oral relugolix (Orgovyx, Relumina) could be used to suppress testosterone in men with advanced prostate cancer compared to leuprolide (Lupron). This study showed that relugolix was associated with more rapid and effective suppression of testosterone levels when compared to leuprolide. 

Long-acting luteinizing hormone-releasing hormone (LHRH) agonists such as leuprolide are used in the treatment of advanced prostate cancer. They are used to achieve very low levels of testosterone (male sex hormone). When this is achieved, it is called castration levels. Using a LHRH agonist often results in an initial testosterone surge. This often causes adverse reactions such as bone pain and urinary obstruction symptoms. Guidelines recommend adding an anti-androgen agent after starting an LHRH to prevent these side effects.

Relugolix is an oral gonadotropin-releasing hormone (GnRH) antagonist that can be given daily. This has been shown in other studies to lower testosterone levels without the need to add an anti-androgen to stop an initial testosterone surge. The efficacy and safety of oral relugolix when compared to leuprolide in patients with advanced prostate cancer are still under investigation.

There were 934 patients with advanced prostate cancer in this study. Patients were randomly assigned to receive either relugolix (622) or leuprolide (308). The relugolix group were given 120mg tablets daily following an initial dose of 360mg. The leuprolide group were given 22.5mg (11.25mg in Japan) by injection every 3 months. The average follow-up was 52 weeks.

Sustained testosterone suppression (TS) was achieved in 96.7% of the relugolix group. TS was achieved by 88.8% of the leuprolide group. The relugolix group had a faster TS rate below castration levels of 4 days. The leuprolide group had an initial surge of testosterone which eventually reduced to below castration levels by day 29. 

The use of relugolix avoided the use of an anti-androgen to deal with an initial surge of testosterone seen in leuprolide. A higher percentage of patients treated with relugolix had testosterone recovery to normal ranges after 90 days when compared to the leuprolide group (54% vs. 3%)

The most common side effect in both groups was hot flushes (54.3% – relugolix vs 51.6% – leuprolide). Major cardiovascular side effects such as heart attack or stroke occurred less frequently with relugolix (2.9%) compared with leuprolide (6.2%). 

This study concluded that relugolix achieved fast and effective testosterone suppression that was superior to leuprolide in men with advanced prostate cancer. 

This clinical trial served as the basis for FDA approval of relugolix for the treatment of patients with advanced prostate cancer. The study was funded by Myovant Sciences, the manufacturer of relugolix.