Programmed death-ligand 1 (PD-L1) is a protein that can be found in cancer tissue using a PD-L1 test. This includes testing a tissue sample to determine eligibility and predict a potential response to certain treatments.
The results of PD-L1 testing help guide decision-making around the choice of immunotherapy treatments, particularly in cases of triple-negative breast cancer (TNBC).
What is PD-L1’s role in breast cancer?
PD-L1 is a protein that exists naturally within the body. It helps keep the body’s immune response under control. While PD-L1 may be found on normal cells, greater amounts are present on cancer cells. PD-L1 can bind to another protein called PD-1, which is found on T cells, and this is problematic because it prevents T cells from killing PD-L1-expressing cells. Certain immunotherapy drugs can block the two proteins from binding, allowing them to kill these cancerous cells.
PD-L1 is a biomarker in several types of cancer and testing helps guide treatment choices. In breast cancer, PD-L1 testing is not systematically performed, as it is more relevant for patients with TNBC. In these cases of breast cancer, PD-L1 testing helps predict how a patient will respond to immune checkpoint inhibitors (ICI), a type of immunotherapy. If patients show PD-L1 expression, it is used as a biomarker when deciding on eligibility for certain treatments.
Results are given as a Combined Positive Score (CPS). Possible results include:
- CPS ≥10: PD-L1 positive and eligible for specific ICI treatments
- CPS <10: PD-L1 negative and not eligible for specific ICI treatments
Decisions on treatment also take into consideration a number of other factors, including:
- Breast cancer subtype
- Stage and progression of the cancer
- Other tumor biomarkers
- Overall health
- Personal treatment preferences
Your oncologist and healthcare team will recommend the best treatment to fit your individual case.
What can I expect during a PD-L1 test?
A sample of cancerous tumor tissue is tested in a pathology laboratory to measure the amount of PD-L1 on the cancer cells and immune cells. This sample may come from a biopsy of the tumor, in which a long needle is inserted into your skin to extract the sample.
The laboratory uses immunohistochemistry to see if PD-L1 is present. The scoring system provides an assessment that is used to determine which immunotherapy treatment is appropriate.