Nikita V Baclig, Madhuri Chengappa, Andrew J Soliman, Saya Jacob, Alexis LeVee, Samantha Fisch, Carolyne Face, Saliha Chaudhry, Dame Idossa, Thejaswi Poonacha, Laura Huppert, Laura Quintal, Michelle Melisko, Melanie Majure, Karen Tsai, Austin Kordic, Jo Chien, Joanne Mortimer, Hope S Rugo, Melissa G Lechner, Anne Blaes, Kelly E McCann
In this multi-institutional real-world cohort of mBC patients treated with ICIs, irAEs were more frequent than reported in breast cancer clinical trials. ICI duration and CDK4/6 inhibitor use increased irAE risk, while baseline albumin influenced survival. Mild-to-moderate irAEs were associated with improved outcomes, but severe irAEs portended worse survival. These findings support risk-stratified ICI use in mBC.
BACKGROUND: Immune checkpoint inhibitors (ICIs) are increasingly used in metastatic breast cancer (mBC), yet real-world data on immune-related adverse events (irAEs) are limited.
PATIENTS AND METHODS: We conducted a retrospective cohort study across 4 NCI-designated cancer centers. Adults with mBC treated with ICIs between 2014 and 2024 were included. irAEs were defined by provider attribution or treatment with high-dose corticosteroids and exclusion of other clear causes. Predictors of irAE were assessed using multivariable logistic regression. Overall survival (OS) was evaluated using a 12-week landmark analysis.
RESULTS: Among 522 patients (mean age 55.4), most received pembrolizumab (83.9%) and ICI in combination (82.7%). Over a median follow-up of 17.5 months, 42.5% experienced ≥1 irAE and 13.2% had severe (grade 3-4) events. Lower odds of irAE were observed for Black race (OR 0.43; P = .028), low albumin (OR 0.50; P = .007), and low hemoglobin (Hgb) (OR 0.60; P = .009), while higher odds were associated with age 46-55 (OR 1.76, P = .035), CDK4/6 inhibitor use (OR 1.82; P = 0.030) and ≥4 ICI cycles (OR 1.70; P = .007). Among 332 patients included in the landmark analysis, grade 1-3 irAEs were associated with superior OS compared with no irAE, whereas grade 4 irAEs were associated with inferior OS (log-rank P < .0001).
CONCLUSION: In this multi-institutional real-world cohort of mBC patients treated with ICIs, irAEs were more frequent than reported in breast cancer clinical trials. ICI duration and CDK4/6 inhibitor use increased irAE risk, while baseline albumin influenced survival. Mild-to-moderate irAEs were associated with improved outcomes, but severe irAEs portended worse survival. These findings support risk-stratified ICI use in mBC.