Background: Androgen deprivation therapy (ADT) with gonadotropin-releasing hormone (GnRH) receptor agonists or antagonists are the foundation of advanced prostate cancer (aPC) treatment. Relugolix is an oral non-peptide GnRH receptor antagonist approved in the US for the treatment of aPC. In the phase 3 HERO trial, relugolix maintained suppression of testosterone to castration levels in 96.7% of men from Day 29 to 48 weeks, with superiority to leuprolide acetate. Relugolix was well tolerated and associated with a 54% lower risk of major adverse cardiovascular events relative to leuprolide acetate (Shore N, NEJM 2020;382;23). The goal of this current study (OPTYX) is to generate real-world evidence about the safety and effectiveness of relugolix in patients with prostate cancer during routine clinical care. Methods: This prospective observational cohort study (registry) is enrolling patients who have planned initiation with relugolix within 1 month prior to the time of study enrollment. The study is designed to prospectively understand the actual experience of patients with prostate cancer treated with relugolix through data collection on patients selected for treatment, treatment patterns, adherence, patient reported quality of life (QoL) and safety data. Additionally, a better understanding of the trajectory of patients with prostate cancer following cessation of relugolix therapy will be gained by observing the clinical course of the disease, health outcomes, and health-related quality-of-life (HRQoL) in these patients. Inclusion criteria include patients > 18 years old with prostate cancer and planned total treatment with relugolix of at least 4 months. Estimated enrollment is 1000 patients, and patients will be followed for up to 5 years. In addition to assessing routine clinical care and disease progression, patient reported outcomes will be assessed with the Functional Assessment of Cancer Therapy-Prostate (FACT-P) for HRQoL and Simplified Medication Adherence Questionnaire (SMAQ) for adherence at 3 and 6 months then every 6 months. Clinical trial information: NCT05467176.