63 Background: Metastatic castration-resistant prostate cancer (mCRPC) is a lethal disease with significant morbidity. Poly adenosine diphosphate-ribose polymerase inhibitors (PARPi) are targeted therapeutics approved to treat mCRPC patients with genetic mutations in homologous recombination repair (HRR). However, to benefit from PARPi as a single agent, patients usually need to undergo biomarker testing to determine their mutation status. As an initial step to understand patient preferences for mCRPC treatments, this study investigated the treatment features important to mCRPC patients and their preferences for and perceptions of biomarker testing. Methods: This preliminary qualitative study included 25 men in the US, UK, Germany, Spain, and Japan with self-reported mCRPC diagnosed at least 6 months previously. Participants completed a 60-minute one-on-one interview about mCRPC treatments and disease impact. Results: Participants had a mean age of 62 years and were diagnosed with prostate cancer an average of 68 months prior. About half (52%) had metastasized > 1 year prior and more than half (56%) reported no HRR genetic mutation . The most frequently reported symptoms were pain (60%), urinary problems (56%), and fatigue (32%). Participants stated that pain impacted their sleep, daily activities, and social lives. 60% reported they shared treatment decision-making with their physician, some (24%) shared it with partners or caregivers, and others (32%) left treatment decisions up to their physician due to their lack of knowledge. Quality of life (QoL) was the most important treatment benefit reported (56%), followed by progression-free survival (PFS) (52%), overall survival (OS) (48%), and reduced pain (44%). Some participants reported their desire for prolonged survival needed to be balanced with adequate QoL. Few participants reported reduced fatigue (24%) or urinary problems (12%) as desired treatment benefits. 64% had previously undergone biomarker testing to determine mutation status. 56% of tested participants reported that their physician discussed the purpose and benefits of testing. Based on conversations with their physicians, both tested and untested participants felt that biomarker testing would inform them about heritable risk of mutation and help find new targeted treatments. Untested participants with a negative view of biomarker testing (22%) reported concerns about the need for further invasive biopsies. Conclusions: QoL followed by PFS, OS, and reduced pain were the most important benefits of treatment to participants. More than half of participants had a positive view of biomarker testing, especially if testing could lead to targeted therapies and inform about heritable risk. These results will inform the design of an international discrete choice study of biomarker testing among men with mCRPC.