Biomarker
PD-L1 Expression
Also known as: PD-L1 status, PD-L1 positivity, PD-L1 tumor proportion score
Definition
The level of PD-L1 protein present on tumor cells or immune cells, used as a biomarker to predict response to immunotherapy.
Detailed Explanation
PD-L1 expression is measured as a percentage of tumor cells that stain positive for PD-L1 protein. Higher PD-L1 expression (≥50%) often predicts better response to PD-1/PD-L1 inhibitors, though responses can occur at lower levels. Testing is done via immunohistochemistry on tumor biopsy samples. Different assays exist (22C3, 28-8, SP142), and thresholds vary by cancer type.