# What is PD-L1 testing?

Source: https://oncologyistanbul.com/glossary/pd-l1-testing

> A test measuring how much PD-L1 protein a tumor expresses, used to help predict whether immune-checkpoint immunotherapy is likely to help.

PD-L1 (programmed death-ligand 1) is a protein some tumor cells use to evade the immune system. Measuring its expression level on tumor tissue helps oncologists gauge — though not guarantee — how likely a checkpoint-inhibitor immunotherapy drug is to be effective, and is one factor among several the tumor board weighs when considering immunotherapy.

## Related
- [Immunotherapy](https://oncologyistanbul.com/treatments/immunotherapy)

Full glossary: https://oncologyistanbul.com/glossary