182eTiP Prospective tumour immune microenvironment profiling with integrated plasma extracellular vesicle multi-omic analysis in early-stage triple-negative breast cancer treated with neoadjuvant therapy

Results: 42 studies including 8,317 patients met inclusion criteria.Pooled discordance rates were 19.8% (95% CI 16.9-23.0)for ER, 32.5% (28.4-36.9)for PR, 11.6% (9.1-14.6)for HER2, and 36.9% (30.7-43.6)for Ki-67.Directional changes included ER loss in 13.4% and HER2 gain in 6.8%.Discordance was higher in visceral vs bone metastases (OR 1.42, 1.18-1.71)and after prior endocrine or anti-HER2 therapy.Biomarker reassessment led to treatment modification in 21-28% and was associated with improved progression-free survival when therapy matched metastatic status (HR 0.72-0.84).Conclusions: Primary metastatic biomarker discordance in breast cancer is frequent and clinically consequential, directly influencing therapeutic decisions and outcomes.Routine biopsy and molecular reassessment of metastatic disease should be integrated into clinical pathways to enable truly precision-based treatment and optimize survival.