PDL1 (Immunotherapy) Tests

What is PD-L1?

Programmed death-ligand 1 (PD-L1) is a protein expressed on the surface of some tumor cells and on various immune cells. It is used as an immunotherapy target to help the body’s own immune system fight cancer. PD-L1 testing can help determine a patient's eligibility for immunotherapy treatment.

How does PD-L1 testing work?

PD-L1 testing is a laboratory procedure based on immunohistochemistry (IHC) and/or in situ hybridization (ISH) techniques. To use PD-L1 testing, a sample of the patient's tumor is taken and analyzed for the presence of PD-L1. If PD-L1 is present in the sample, then the patient may be eligible for immunotherapy.

Types of PD-L1 Tests

There are two types of PD-L1 tests:

• Immunohistochemistry (IHC): This test measures the amount of PD-L1 protein on tumor cells by staining the sample with a PD-L1-specific antibody. The intensity of the staining is then evaluated and used to predict the patient's response to immunotherapy.
• In Situ Hybridization (ISH): This test is used to detect gene expression of PD-L1 in tumor cells. ISH is often used to complement IHC testing and to provide an additional layer of information.

Preparation for PD-L1 Testing

PD-L1 testing is usually performed on a sample of the patient's tumor. Depending on the type of PD-L1 test used, the sample needs to be prepared in different ways. For IHC testing, the sample needs to be formalin-fixed and paraffin-embedded (FFPE). This means the sample needs to be preserved with formalin before being embedded in paraffin wax. For ISH testing, the sample needs to be snap-frozen or fresh-frozen.

Benefits of PD-L1 Testing

PD-L1 testing is used to determine a patient's eligibility for immunotherapy. For some patients, immunotherapy is more effective than chemotherapy or radiation therapy. The results of PD-L1 testing can help doctors tailor the most effective treatment plan for each patient and avoid ineffective treatments. It can also help reduce the risk of side effects associated with certain therapies.

Risks of PD-L1 Testing

PD-L1 testing is generally considered safe since the sample is taken from the patient's tumor. However, it is important to note that the sample can be contaminated with normal cells which may lead to false positive results. Additionally, the results of the test may not be conclusive and the doctor may need to take other factors into consideration when selecting the most appropriate therapy for the patient.

When to Get Tested

PD-L1 testing is typically recommended for patients with advanced cancer. However, some types of cancer are known to respond better to immunotherapy than others, so the doctor may decide to test a patient even if the cancer is in the early stages. Additionally, many clinical trials focus on the use of immunotherapy in combination with other treatments or protocols so PD-L1 testing may be recommended in those cases as well.