Abstract P4-02-02: Hospitalizations and emergency visits for Ontario breast cancer patients undergoing neoadjuvant chemotherapy with pembrolizumab: A population-based analysis

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Abstract Background: Immunotherapy-containing chemotherapy regimens are increasingly used for the neoadjuvant treatment of triple negative breast cancer (BC). However, these regimens can be associated with immune-related adverse events, which may lead to increased hospitalizations and emergency department (ED) visits. The objective of this study was to assess the rate of hospitalization and ED visits for BC patients undergoing neoadjuvant chemotherapy (NAC) with and without immunotherapy in Ontario, Canada. Methods: Breast cancer patients who underwent NAC and surgery between April 1, 2022 and August 31, 2023 were included. Neoadjuvant chemotherapy regimens were classified into three groups containing either pembrolizumab, an anti-HER2 drug, or chemotherapy alone. The proportion of patients who had ED visits or were hospitalized during the neoadjuvant period (first date of chemotherapy to the day of surgery) and the post-operative period (day of surgery to 30 days after surgery) were calculated. Rates and 95% CI of ED visits and hospitalizations during each time period per patient per year were analyzed. Results: The study cohort consisted of 1301 newly diagnosed BC patients who had systemic therapy before surgery with a median age of 52 (44 - 62); 94.7% of patients had no previous comorbidities. A total of 229 patients (17.6%) received a regimen with pembrolizumab, 532 (41%) had an anti-Her 2 agent, and 540 (41.4%) had chemotherapy alone. The proportion of patients on pembrolizumab who had one or more ED visits during the neoadjuvant period was significantly higher (54.6%) than patients on anti-HER2 (42.3%) or chemotherapy alone (40.0%; p < 0.001). The rate of ED visits was also higher for the pembrolizumab cohort at 2.81 visits per patient per year (95% CI: 2.52-3.15) compared to anti-HER2(1.95 [95% CI: 1.77-2.15]) or chemotherapy alone groups (1.74 [95% CI 1.57-1.93]). However, there was no significant difference in ED visits in the post-operative period between the groups (pembrolizumab: 18.3%, anti-HER2: 14.5%, chemotherapy alone: 14.4%, p=0.33). The rate of ED visits in the post-operative period was also similar: pembrolizumab: 2.67 visits per patient per year (95% CI: 2.04 – 3.51), anti-HER2: 2.10 (95% CI: 1.72 – 2.77), chemotherapy alone: 2.35 (95% CI 1.95 – 2.85). Hospitalization was more frequent among patients receiving pembrolizumab pre-operatively (pembrolizumab: 32.3%, anti-Her2: 15.2%, chemotherapy alone: 11.1%; p < 0.01), but there were no significant differences in hospitalization after surgery. Conclusion : Breast cancer patients undergoing neoadjuvant therapy including pembrolizumab had higher rates of ED visits and hospitalizations before surgery compared to those receiving anti-HER2 therapy or chemotherapy alone. However, differences in these outcomes were not seen in the post-operative period. This study provides confirmatory population-level data regarding the integration of immunotherapy into NAC. Further work to understand the etiology and mitigate unanticipated health care utilization for BC patients undergoing NAC is needed. Citation Format: Gary Ko, Eitan Amir, Matthew Castelo, Andrea Covelli, Antoine Eskander, Vivianne Freitas, C. Anne Koch, Qing Li, Ning Liu, Jenine Ramruthan, Emma Reel, Amanda Roberts, Toni Zhong, Tulin D. Cil. Hospitalizations and emergency visits for Ontario breast cancer patients undergoing neoadjuvant chemotherapy with pembrolizumab: A population-based analysis [abstract]. In: Proceedings of the San Antonio Breast Cancer Symposium 2024; 2024 Dec 10-13; San Antonio, TX. Philadelphia (PA): AACR; Clin Cancer Res 2025;31(12 Suppl):Abstract nr P4-02-02.

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