Immune Checkpoint Inhibitors: Clinical Advances and Biomarker-Driven Patient Selection

Immune checkpoint blockade has transformed the treatment landscape of numerous cancers, yet durable responses remain limited to a subset of patients. This chapter reviews the clinical development and approved indications of PD-1, PD-L1, CTLA-4, and emerging checkpoint inhibitors across tumor types, with a focused discussion on validated and investigational predictive biomarkers — including tumor mutational burden, microsatellite instability, and PD-L1 expression — that guide patient selection and optimize therapeutic outcomes.