What Is a PD-L1 Test?

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Credit: John Digianni

A PD-L1 test helps doctors determine whether a patient is likely to benefit from cancer drugs known as immune checkpoint inhibitors. It involves sending a piece of tumor tissue to a lab for analysis.

PD-L1 is a protein that allows some cells to escape an attack by the immune system. Extending from the cancer cell surface, PD-L1 interacts with a protein called PD-1 on important immune system cells called T cells. This coupling – known as an immune checkpoint – instructs the T cell to leave the tumor cell alone. Checkpoint inhibitor drugs prevent the PD-1/PD-L1 meeting from taking place. Without receiving the “stop” signal from the PD-L1 protein, the T cells can go ahead an attack the tumor cells.

Drugs inhibiting the PD-1/PD-L1 checkpoint have been approved by the Food and Drug Administration for several cancers – including lung, bladder, and kidney cancers, squamous cell cancer of the head and neck, and Hodgkin lymphoma – and are in clinical testing for a variety of other cancer types. A PD-L1 test measures how much PD-L1 a tumor “expresses,” or produces. Tumors that express high amounts of PD-L1 may be more susceptible to checkpoint inhibitors than those that express less. Patients should ask their cancer physicians whether a PD-L1 test is appropriate for them.

Although helpful in determining which patients may respond to certain drugs, the test is not infallible. Some tumors that test for high levels of PD-L1 may not respond to checkpoint inhibitors, and those that test for low levels may have a strong response. Cancer cells are complex, and a variety of factors can influence how susceptible they are to such drugs.

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2 thoughts on “What Is a PD-L1 Test?

  1. I have esophogeal cancer and it doesn’t look good for surgery. I went to J.H. in Baltimore a couple weeks ago and I’m interested in the immunotherapy clinical trials as an alternative to the chemo I’ve been getting for more than a year; many, many side effects….
    This test was mentioned and I’m going to get that tumor sampled.
    Thank you for the good information!

  2. Neil as you go through your battle. You are being treated by the best in the world, I am praying for a full remission and with the help of God and the Dana Farber I know you will make it.

  3. Neil as you go through your battle. You are being treated by the best in the world, I am praying for a full remission and with the help of God and the Dana Farber I know you will make it.

  4. I have esophogeal cancer and it doesn’t look good for surgery. I went to J.H. in Baltimore a couple weeks ago and I’m interested in the immunotherapy clinical trials as an alternative to the chemo I’ve been getting for more than a year; many, many side effects….
    This test was mentioned and I’m going to get that tumor sampled.
    Thank you for the good information!

Comments are closed.

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