An Expert Review on the Combination of Relugolix With Definitive Radiation Therapy for Prostate Cancer

Abstract

Androgen deprivation therapy (ADT) is an integral component in the management of prostate cancer across multiple disease states. Traditionally, luteinizing hormone-releasing hormone (LHRH) agonists constituted the backbone of ADT. However, gonadotropin-releasing hormone receptor hormone (GnRH) antagonists also are available, which offer faster testosterone suppression and reduced likelihood of ADT-related adverse effects compared with LHRH agonists, including the potential for fewer ADT-associated major cardiac events. Until recently, all forms of LHRH agonists and GnRH antagonist formulations were of parenteral administration. However, recently relugolix gained Food and Drug Administration approval as the first oral GnRH antagonist. Relugolix achieves faster and more complete testosterone suppression compared with an LHRH agonist. This translates to more rapid prostate-specific antigen response compared with LHRH agonists. After discontinuation of relugolix, testosterone recovers faster than after GnRH agonists or injectable GnRH antagonist therapy. Overall, these factors provide opportunities for more precisely defined ADT duration when combined with radiation therapy. The rapid onset and offset of testosterone suppression with relugolix may require physicians to rethink the mechanism and goals of ADT when prescribing. As an oral formulation, relugolix enables patients to avoid pain and injection site reactions, limit extra office visits for injections, and achieve a shorter duration of experiencing the side effects of castrate testosterone levels. This convenience and tolerability may enhance physicians' willingness to prescribe ADT and patients' feeling of control during their ADT course, but the potential advantages are accompanied by the risks of patients choosing to discontinue therapy to escape side effects of ADT. This article focuses on different aspects of what is known and unknown regarding the optimal use of ADT and radiation therapy, and how relugolix, due to its properties, fit into our current treatment paradigms for localized prostate cancer.