What is a PD-L1 Test?

A PD-L1 test uses a sample of cancerous tumor tissue to measure how much of a protein called PD-L1 is found on the cancer cells. If you have certain types of cancer, PD-L1 testing can check whether you may benefit from a type of cancer treatment called immunotherapy. Immunotherapy helps your own immune system fight cancer.

Normally, PD-L1 is found on certain healthy cells. It acts as a kind of "brake" to stop cells in your immune system, called T cells, from attacking healthy cells in your body. If cancer cells have high amounts of PD-L1, they can turn your T cells off so they can't attack the cancer cells.

If high amounts of PD-L1 are found on cancer cells, immunotherapy medicines called "immune checkpoint inhibitors" may be used. These medicines prevent the PD-L1 protein from putting the brakes on T cells. This frees your T cells to fight cancer.

Immunotherapy can help stop or slow the growth of many types of cancers that have PD-L1. Immunotherapy has fewer side effects than cancer chemotherapy. But it can cause serious side effects in some people, and not everyone benefits from it.

There are many types of PD-L1 tests. The test your health care provider orders will depend on:

• The type of cancer you have
• The specific immunotherapy medicine that your provider is considering for you

Other names: programmed death-ligand 1, PDLI, PDL-1 by immunohistochemistry (IHC)

What is it used for?

PD-L1 testing is used to look for the PD-L1 protein on cancer cells in a sample of tumor tissue. The test also measures the amount of PD-L1 in the tissue. This information helps find out if immunotherapy medicines could help control your cancer.

Why do I need a PD-L1 test?

If you've been diagnosed with cancer, you may need PD-L1 testing to find out if immunotherapy could help you. Many types of cancer have immunotherapy treatments related to PD-L1. These cancers include:

• Non-small cell lung cancer
• Melanoma
• Hodgkin lymphoma
• Bladder cancer
• Kidney cancer
• Breast cancer
• Head and neck cancer (squamous cell carcinoma)
• Cancer of the esophagus (squamous cell carcinoma)
• Stomach cancer (adenocarcinoma)
• Cervical cancer

What happens during a PD-L1 test?

PD-L1 tests are done on a tissue sample from a tumor. If you're having surgery to remove a tumor, a sample will be taken for testing.

If you aren't having the tumor removed, you may have a biopsy, which is a procedure to remove a small amount of tissue for testing. If you already had a biopsy to diagnose your cancer, the same tissue sample may be used to test for PD-L1.

There are many ways to do a biopsy. The type of biopsy you have depends on the type of cancer you have and where the tumor is located. In general, a biopsy may be done using:

• A hollow needle inserted through your skin. Imaging tests, such as ultrasound, may be used to guide the needle:
  • A fine needle aspiration biopsy uses a very thin needle to remove a sample of cells and/or fluid.
  • A core needle biopsy uses a larger needle to remove a sample.
• Surgery. Surgery may be done to remove a sample of tissue (an incisional biopsy). In certain cases, the entire tumor will be removed (an excisional biopsy).
• A scope. Scopes are tools for looking inside your body. They may be inserted through an opening in your body or through a small incision (cut). Special tools may be used with a scope to remove a tissue sample. Examples of scope procedures include bronchoscopy, laparoscopy, colposcopy, and cystoscopy (to examine the inside of the bladder).

Will I need to do anything to prepare for the test?

Preparations for your test depend on how your tissue sample will be taken. Ask your provider how to prepare for your test.

Are there any risks to the test?

Risks depend on how your tissue sample is taken. In general, if you are having a biopsy, you may have a little bruising or bleeding where the tissue was removed. Ask your provider to explain any risks from the test you're having.

What do the results mean?

Your test results will show whether you have enough PD-L1 protein in your tumor for you to benefit from a specific immunotherapy medicine. Some immunotherapy medicines will not be helpful if a small percentage of your cancer cells have PD-L1.

If your test results show that:

• Your tumor cells have enough PD-L1 for you to use immunotherapy medicine, you may be able to start that medicine. This may be called a "positive" test result.
• Your tumor cells don't have enough PD-L1, then the immunotherapy is not likely to help you. This may be called a "negative" test result. Your provider will consider another type of cancer treatment.

Your provider may also use other tests to help decide on the best treatment for you. If you have questions about your results, talk with your provider.

Learn more about laboratory tests, reference ranges, and understanding results.

Is there anything else I need to know about a PD-L1 test?

Immunotherapy is a quickly changing area of medicine. For some immunotherapy medicines, PD-L1 testing is required to see if you are a good match for that treatment. For other medicines, testing is only recommended. But new research may change how tests are used to choose treatments. So, check with your provider to find out how PD-L1 testing may affect your treatment plan.