Biomarkers
PD-L1 Expression
Also known as: PD-L1 positivity, PD-L1 status
Definition
The level of PD-L1 protein on tumor or immune cells, used to predict response to checkpoint inhibitors.
Detailed Explanation
PD-L1 expression is measured by immunohistochemistry and reported as a percentage of positive cells (TPS for tumor cells, CPS for combined tumor/immune cells). Higher expression generally correlates with better response to PD-1/PD-L1 inhibitors, but patients with low/negative expression can still respond. Multiple testing platforms exist with different scoring systems.