Acute care events among adult patients receiving immuno-oncology treatments.

479 Background: Emergency department (ED) visits and unplanned hospitalizations—collectively referred to as acute care events (ACE)—pose a substantial burden on patients and health systems. A large proportion of ACEs are considered potentially preventable. Despite immuno-oncology (IO) regimens becoming a mainstay of cancer treatment, little is known about preventable ACEs in patients receiving IO compared to chemotherapy. Methods: We conducted a retrospective cohort study using electronic health record (EHR) data from adults aged 21+ with cancer who initiated a new course of systemic anticancer therapy in 2022 (as evidenced by no therapy administration in the preceding 6 months) across a tertiary academic medical center and its affiliated community sites. The primary outcome was the occurrence of an ACE within 30 days of treatment plan initiation. Consistent with the CMS OP-35 measure, potentially preventable ACE indications were identified using primary discharge diagnosis codes. Rates and types of ACEs were compared across three groups: chemotherapy only (CHEMO), immunotherapy only (IO), and combination therapy (CHEMO-IO). Results: Among a cohort of 4232 patients, 3101 (73.3%) initiated CHEMO, 637 (15.1%) initiated IO, and 494 (11.7%) initiated CHEMO-IO. The 30-day ACE incidence was highest in the CHEMO-IO group (24.7%; 122/494), followed by CHEMO (16.4%; 509/3,101) and IO (14.6%; 93/637). Among ACE encounters, the proportion classified as potentially preventable was greatest in the CHEMO group (27.3%; 175/642), compared to CHEMO-IO (25.2%; 38/151) and IO (21.6%; 27/125). The most common preventable ACEs included pain (7.5% CHEMO, 8.8% IO, 6.6% CHEMO-IO), pneumonia (1.9% CHEMO, 2.4% IO, 4.0% CHEMO-IO), and sepsis (6.5% CHEMO, 5.6% IO, 7.9% CHEMO-IO). Conclusions: Patients initiating IO experienced similar rates of ACE compared with CHEMO, although those initiating combination CHEMO-IO faced the highest ACE rates. Patterns of ACE diagnoses differed across treatment groups. Findings underscore the importance of targeted supportive care strategies to reduce preventable ACEs while maintaining high-quality care for patients receiving systemic treatments for cancer.