Longitudinal cytokine and transcriptomic profiling of immune-related adverse events in early-stage TNBC treated with pembrolizumab.

e12640 Background: Pembrolizumab-based chemo-immunotherapy improves outcomes in early-stage triple-negative breast cancer (TNBC) but frequently complicated by immune-related adverse events (irAEs) that impact treatment delivery and survivorship. Predictive biomarkers for irAE remain limited with most studies relying on baseline immune profiling. We evaluated longitudinal cytokine and transcriptomic patterns associated with irAE development in early-stage TNBC patients receiving pembrolizumab-based chemo-immunotherapy. Methods: We conducted a retrospective analysis of 28 patients; 13 developed grade ≥2 irAEs and 15 did not. Plasma and buffy coat samples were collected at baseline and at 1, 2, 3, 6, 9, and 12 months after pembrolizumab initiation. Cytokines were quantified using a comprehensive panel. Baseline associations with irAE development were evaluated using univariate Cox proportional hazards models with Q-value adjustment. Longitudinal cytokine trajectories were evaluated using mixed-effects models with false discovery rate (FDR) correction. Genes corresponding to significant cytokines (FDR < 0.2) were mapped to Reactome and KEGG pathways and overlapped with a predefined 194-gene inflammatory and neuroimmune mRNA panel, followed by longitudinal mixed-effects modeling. Results: At baseline, lower circulating levels of TNF-α (HR 0.54, p = 0.024, FDR = 0.152), IL-10 (HR 0.54, p = 0.035, FDR = 0.152), and IL-8 (HR 0.54, p = 0.009, Q = 0.122) were associated with development of grade ≥2 irAEs. Longitudinal analyses demonstrated distinct immune trajectories in patients who developed irAEs. IL-12p70 levels increased significantly at multiple on-treatment and post-treatment time points (months 2, 6, 9,12), while TNF-α increased at 12 months, suggesting sustained inflammatory activation. In contrast, MCP-1 levels declined during early treatment (month 3) among irAE patients. Integration of cytokine and transcriptomic data identified 19 overlapping genes. Longitudinal gene expression analyses revealed increased expression of IL12B and CXCL12 at later time points and decreased expression of ICAM1 and CCR2 during treatment in patients with irAEs. Six key markers (TNF-α, IL-10, IL-8, IL-12, ICAM1, and CXCL12) converged on NF-κB–related inflammatory signaling pathways. Conclusions: In early-stage TNBC treated with pembrolizumab-based chemo-immunotherapy, irAE development was associated with dynamic longitudinal immune changes rather than baseline cytokine levels alone. Integrated cytokine and transcriptomic profiling implicates NF-κB–related inflammatory pathways in irAE biology and supports longitudinal immune monitoring to improve irAE risk stratification. These exploratory findings require validation in larger cohorts but suggest biomarker trajectories that may inform future therapeutic development.