Real-world utilization patterns and adverse events among patients receiving antibody–drug conjugates (ADCs) across the University of California health system.

11118 Background: Antibody–drug conjugates (ADCs) have rapidly expanded across oncology indications, yet real-world safety profiles remain incompletely characterized. Pivotal trials may not fully capture adverse events (AEs) associated with real-world treatment patterns, such as cumulative exposure or sequential ADC therapy. Methods: We performed a retrospective cohort study across six UC medical centers using de-identified structured EHR data from the University of California Health Data Warehouse (UCHDW). We included adult patients who received at least 1 dose of ADC between Jan 2015 and Feb 2025. Observational period for safety surveillance is at least 8 months. Key safety outcomes were the incidence and timing of key AEs following ADC initiation. Secondary outcomes included duration of ADC therapy and the frequency of sequential ADC. Descriptive statistics were used to analyze toxicity and time to AE of special interest. Results: Across the UC system, 4,531 patients received at least one ADC and had a documented cancer-related diagnosis, 82.7% of patients had metastatic cancer at initiation of ADC. Breast cancer was the most frequently observed cancer type (38.8%), followed by hematologic malignancies (28.5%) and bladder/urothelial cancers (11.2%). Mean dose number was 10.1 (standard deviation: 11.3). Among 4,531 ADC-treated patients, 10.6% transitioned to a second ADC, and 78.9% received concomitant anticancer therapy, including immune checkpoint inhibitors (38.0%), ICI plus chemotherapy (21.8%), or chemotherapy alone (18.7%). Incident neurotoxicity was the most frequent AE (728 patients, 16.1%), followed by hematologic (15.0%) and cardiotoxicity (14.6%) AEs. Incident ocular toxicity was observed in 343 patients (7.5%) with a median time to onset of 84 days, and incident mononeuritis in 480 patients (10.6%) with a median onset of 105 days following ADC initiation. Conclusions: In this large, multi-center real-world cohort, ADC treatment was associated with substantial rates of neurologic, hematologic, and cardiac toxicities. The frequent use of concomitant anticancer treatments and observed transitions between ADCs underscore the complexity of real-world exposure and highlight the need for proactive toxicity monitoring and optimized safety management strategies in routine oncology practice.