Emerging biomarkers of immune checkpoint inhibitor toxicity in triple-negative breast cancer: a mini-review.

Immune checkpoint inhibitors (ICI) have revolutionized the treatment of TNBC, leading to durable responses and improved survival. With the adoption of immunotherapy into high-risk early-stage and selected metastatic triple-negative breast cancer (TNBC), clinicians' ability to recognize and treat immune-related adverse events has become increasingly important. There is no prospectively validated or FDA-approved predictive biomarker of toxicity; however, candidate biomarkers involving circulating blood counts, immune-cell phenotypes, cytokines, transcriptomics, immune age, germline genetics, human leukocyte antigen genotypes, autoantibodies, and the gut microbiome have been described, with many more currently under investigation. Most evidence remains exploratory and is derived from non-TNBC populations. Going forward, incorporating these investigational tools within prospective TNBC trials and validating them in real-world, multicenter TNBC cohorts are critical to ensure these predictive biomarkers translate into clinically useful tools for risk-adapted monitoring. This mini-review highlights the current landscape of predictive biomarkers of ICI toxicity, with a focus on TNBC.