Abstract PS2-02-01: Improved Antiemetic Outcomes with NEPA vs (Fos)aprepitant in Patients with Breast Cancer Receiving Antibody-Drug Conjugates: A 12-Month Real-World Claims Analysis

Abstract Background: Antibody-drug conjugates (ADCs) are increasingly used to treat breast cancer (BC) and are often administered over prolonged periods. While nausea and vomiting (NV), including long-delayed nausea, are well-established side effects, limited real-world evidence exists evaluating antiemetic outcomes over extended treatment durations. This analysis evaluated 12-month real-world clinical and economic outcomes in U. S. patients with BC receiving ADCs, using national claims data. Outcomes were assessed for NCCN-guideline recommended antiemetic agents: NEPA (netupitant/palonosetron), distinguished by its prolonged NK1 receptor occupancy and extended half-life, and fos (aprepitant). Methods: A retrospective claims analysis using the STATinMED RWD Insights all-payer medical and pharmacy claims database evaluated patients with BC treated between January 1, 2019, and December 31, 2023. The index date was defined as the earliest claim for either NEPA or (fos) aprepitant. Eligible patients were ≥18 years with a BC diagnosis who received one of three ADCs—trastuzumab emtansine (T-DM1), trastuzumab deruxtecan (T-DXd), or sacituzumab govitecan (SG) —and maintained continuous medical and pharmacy benefits for 12 months before and after the index date. To minimize confounding, 1: 1 propensity score matching was conducted to create balanced cohorts for NEPA vs fos (aprepitant) based on demographics and clinical variables including sex, geographic region, payer type, and comorbidity burden. Clinical outcomes were compared for NEPA vs (fos) aprepitant and included claims for nausea or vomiting or related complications (i. e. , dehydration, IV fluid use, and/or electrolyte imbalance) occurring at least once during the 12-month evaluation period. Nausea occurring 72 h after the index date was also assessed. Outpatient hospital services (i. e. , hospital-based care not involving admission or emergency treatment) and outpatient and emergency room costs were also determined for the two cohorts. NV-related utilization and costs were identified based on the presence of a NV diagnosis code in any position on the medical claim. Statistical analyses included descriptive statistics and hypothesis testing to evaluate differences between cohorts. Results: In the matched cohort analysis of 209 patients per group (n = 192 T-DM1, n = 154 T-DXd, and n = 72 SG of total population), NEPA had improved clinical and economic outcomes compared with (fos) aprepitant. During the 12-month post-index period, significantly fewer NEPA patients (82. 3%) experienced nausea or vomiting or related clinical complications than (fos) aprepitant patients (90. 4%; p=0. 0154). Nausea rates 72 h were significantly lower for NEPA (27. 8%) compared to (fos) aprepitant (40. 2%; p=0. 0073). Outpatient hospital services related to NV were also significantly lower with NEPA (43. 0%) compared to (fos) aprepitant (69. 4%; p0. 0001). The mean NV-related outpatient and emergency room cost for NEPA was 14, 884, less than half the cost for (fos) aprepitant (30, 665; p0. 0001). While claims data offer valuable insights into real-world treatment patterns and outcomes, they have inherent limitations including potential coding inaccuracies, lack of clinical detail, and incomplete capture of patient-reported outcomes or uninsured care. Conclusion: These findings highlight clinical and economic benefits of NEPA-based antiemetic prophylaxis in patients with BC receiving ADCs. Given that patients often undergo prolonged ADC treatment, selecting an antiemetic regimen with sustained efficacy─such as NEPA in this database analysis─may be particularly important to minimize complications, lower healthcare utilization and cost, preserve quality of life, and support treatment continuity. Citation Format: L. Schwartzberg, T. Gillespie, E. Roeland, T. Tyler, R. Agarwal, A. Alonzi, T. Fralich, P. Mudumby, G. Aweh, M. Fisher, H. Rugo. Improved Antiemetic Outcomes with NEPA vs (Fos) aprepitant in Patients with Breast Cancer Receiving Antibody-Drug Conjugates: A 12-Month Real-World Claims Analysis abstract. In: Proceedings of the San Antonio Breast Cancer Symposium 2025; 2025 Dec 9-12; San Antonio, TX. Philadelphia (PA): AACR; Clin Cancer Res 2026;32 (4 Suppl): Abstract nr PS2-02-01.