Real world utilization and outcomes of immunotherapy regimens in metastatic castration resistant prostate cancer (mCRPC)

e17038 Background: While immune checkpoint inhibitors (ICIs) have shifted the treatment paradigm in many cancers, their efficacy in mCRPC is limited. Ongoing research suggests distinct subpopulations of mCRPC may derive benefit or that combinatorial regimens including ICIs may overcome treatment resistance. This single-center retrospective study aims to describe real-world utilization patterns of ICIs for patients with mCRPC and assess the treatment effects. Methods: The EHR database was queried for patients with PC who were treated with an ICI outside of a clinical trial. Additional data were obtained from chart review and the cancer registry. Patients were excluded if ICI was given for another cancer type, non-metastatic disease, or as a component of small-cell lung cancer regimens. Kaplan-Meier curves were used to estimate time to events. Results: 31 patients are included in the study. From years 2016 to 2022, 13 patients received ICI alone. Starting in 2019, 18 patients received ICI combined with cabozantinib (C). ICI+C had PSA response rate (RR) of 50%, median duration of treatment (DOT) of 5.5 months, and median overall survival (OS) of 8 months (Table 1). 3 of these patients received therapy for ≥ 12 months. ICI alone had a RR of 0%. 94% of patients who received ICI+C were not a candidate for CONTACT-2 (NCT04446117). Conclusions: Oncologists continue to use ICI for mCRPC. While noncomparative, ICI+C demonstrated favorable activity over a historical cohort of ICI alone. Ongoing clinical trial participation is vital for patients with mCRPC; however, off-label prescribing may provide additional access to treatment options. [Table: see text]