When chemotherapy fails to control metastatic colorectal cancer, treatment shifts from one-size-fits-all to biomarker-driven precision medicine. Molecular profiling of your tumor unlocks targeted therapies, immunotherapy, and trial pathways previously unavailable. Key Takeaways MSI-H or dMMR status determines immunotherapy eligibility; pembrolizumab and nivolumab achieve ~40-50% response rates in this subset RAS wild-type tumors can receive EGFR-targeted therapy (cetuximab, p