Abstract PS5-03: Incidence and Risk Factors of Immune-Related Adverse Events in Early-Stage Breast Cancer Patients: Findings from a Multi-Institutional Study

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Abstract Introduction: With the addition of immune checkpoint inhibitors (ICIs) to the neoadjuvant/adjuvant treatment regimen in early-stage breast cancer, an increasing number of patients (pts) with breast cancer are developing immune-related adverse events (irAE). Identifying risk factors and biomarkers predictive of irAE in pts with early breast cancer is critical to prevent and mitigate irAE and improve ICI outcomes. The aim of this study is to report the incidence and identify predictive biomarkers of irAE in a large cohort of pts with early-stage breast cancer. Methods: We identified pts with stage I-III breast cancer who received ICI at four academic institutions between 2014-2024. Pts were excluded if currently receiving ICI. Charts were reviewed for any grade irAE during or after ICI therapy. The chi-square and Wilcoxon rank-sum tests were used to compare baseline and treatment characteristics. Uni- and multivariate logistic regression was performed to determine factors predictive of severe (grade ≥3) irAE including age at ICI treatment, menopausal status, breast cancer subtype, race/ethnicity, BMI, menopausal status, smoking history, co-morbidities, and baseline laboratory values. Results: Of the 423 pts with early breast cancer included in the analysis, 307 (72.6%) pts developed any grade irAE and 80 (18.9%) pts developed ≥1 grade 3-4 irAE. No deaths (grade 5) due to irAE occurred. Of the 307 pts that developed any grade irAE, 180 (58.6%) pts developed 1 irAE, 97 (31.6%) developed 2 irAE, and 30 (9.8%) developed 3+ irAE. Of the 80 pts that developed severe irAE, 73 (91.3%) pts developed 1 severe irAE, and 7 (8.8%) developed 2 severe irAE. Among the 437 any grade irAE, the most common were thyroiditis (24.3%), rash (23.0%), colitis (14.5%), hepatitis (10.6%), and adrenal insufficiency/hypophysitis (7.6%). Among the 87 severe irAE, the most common were adrenal insufficiency/hypophysitis (20.7%), rash (19.5%), hepatitis (12.6%), colitis (11.5%), and autoimmune diabetes mellitus (8.0%). Patients with irAE received fewer cycles of ICI compared to patients without irAE, with a median number of ICI cycles of 7 (IQR 4-15) and 11 (4-17), respectively (p=0.006). Similarly, patients with severe irAE also received fewer ICI cycles compared to patients without severe irAE, with a median number of ICI cycles of 4 (IQR 3-9) and 9 (4-17), respectively (p<0.0001). Multivariate logistic regression demonstrated that older age (age ≥50y vs. age <50y) [OR 1.69; 95% CI, 1.00-2.86; p=0.05] and the presence of CKD (OR 4.93; 95% CI, 1.59-15.3; p=0.006) were predictive of severe irAE. Conclusion: In this cohort of pts with early-stage breast cancer treated with ICI, the incidence of any and severe irAE was 72.6% and 18.9%, respectively. Pts were more likely to develop severe irAE if they were older and had CKD. Further studies to identify risk factors and biomarkers of irAE in pts with early breast cancer are needed to prevent irAE and reduce the associated long-term complications. Citation Format: Alexis LeVee, Saya Jacob, Samantha Fisch, Carolyne Face, Madhuri Chengappa, Saliha Chaudhry, Nikita Baclig, Andrew Soliman, Nora Ruel, Megan Wong, Karen Tsai, Irene Kang, Laura Huppert, Laura Quintal, Michelle Melisko, Melanie Majure, Jo Chien, Melissa Lechner, Dame Idossa, Anne Blaes, Kelly McCann, Hope S. Rugo, Joanne Mortimer. Incidence and Risk Factors of Immune-Related Adverse Events in Early-Stage Breast Cancer Patients: Findings from a Multi-Institutional Study [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 PS5-03.

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