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  7. PD-L1, PD-1 and TMB

PD-L1, TMB and Lung Cancer

PD-L1 expression and TMB are biomarkers that doctors commonly test for in people with lung cancer to see if immunotherapy may be a treatment option.

PD-L1 and TMB at a Glance:

  • PD-L1 is a protein that may be found on cancer cells. 
  • Doctors test for PD-L1 expression, which measures how much PD-L1 is present in a tumor. 
  • The level of PD-L1 expression may help determine whether immunotherapy could be an effective treatment option.
  • Tumor mutational burden (TMB) measures the number of genetic changes in a tumor. Biomarker testing looks for these markers to help determine whether immunotherapy may be a treatment option. 

Frequently Asked Questions about Biomarker Testing

What Is PD-L1 and TMB?

PD-L1 is a protein that may be found on cancer cells. Doctors use comprehensive biomarker testing to test for PD-L1 expression, which measures how much of this protein is present in a tumor. PD-L1 can bind to PD-1, a receptor protein on immune cells called T cells, and reduce the immune system's ability to attack cancer cells. Some immunotherapy drugs block this interaction, helping the immune system recognize and fight cancer more effectively.  

Doctors test for PD-L1 expression because it may help predict how well certain immunotherapy treatments will work. PD-L1 expression is one of several factors considered when making treatment decisions.

Tumor mutational burden (TMB) is a biomarker that measures the number of genetic changes in a tumor’s DNA.  A tumor with a higher TMB may produce more abnormal proteins that can be recognized by the immune system. As a result, TMB may help doctors determine whether certain immunotherapy treatments could be effective. TMB is one of several factors considered when making treatment decisions.

Watch as Dr. Edward Garon explains tumor mutation burden and how it impacts lung cancer decision making (video). 

Why Testing for PD-L1 and TMB Matters

Biomarker testing for PD‑L1 and TMB is important because these biomarkers can help doctors determine whether immunotherapy is likely to work for a person’s lung cancer and which treatments may offer the most benefit. 

Immunotherapy doesn’t kill cancer directly like chemotherapy. Instead, it helps your immune system recognize and attack cancer cells that were previously "hiding." Immunotherapy activates the immune system to attack these cancer cells. The most common type of lung cancer immunotherapy is called an immune checkpoint inhibitor. Several immune checkpoint inhibitors for lung cancer block, or "inhibit" the interaction between PD-1 and PD-L1.

Dr. Edward Garon explains the role of immunotherapy, PD-L1 and PD-1 in lung cancer. This video was produced in 2020. For the latest treatment options, speak with your doctor.

Video transcript

How Testing for PD-L1 and TMB Is Done

Unlike other biomarkers, PD‑L1 does not require DNA‑based tests such as FISH, NGS, or PCR. PD‑L1 testing looks for the PD‑L1 protein on the surface of cancer cells to help guide immunotherapy treatment. 

At the time of a lung cancer diagnosis, all new patients should have their PD-L1 levels tested. This involves looking at tumor tissue under a microscope using a laboratory technique called immunohistochemical (IHC) staining. A PD-L1 test is reported as a percentage, measuring how much cells in a tumor “express” PD-L1. Tumors that express high amounts of PD-L1 (50% or greater) may respond particularly well to immune checkpoint inhibitors. 

If you have not had your PD-L1 levels tested, ask your doctor if it is right for you. 

TMB is often included as part of comprehensive biomarker testing using next-generation sequencing (NGS). A higher TMB means a tumor has more genetic changes, which may make it easier for the immune system to recognize cancer cells. As a result, some tumors with a higher TMB may be more likely to respond to immunotherapy. 

Learn more about the different types of biomarker tests. 

Understanding Your Test Results

How PD-L1 Levels Influence Treatment

PD-L1 testing is routinely performed on tumor tissue and is reported as a percentage of tumor cells that express PD-L1. If you have high levels of PD-L1 and no other biomarker with an approved targeted therapy, then your doctor will likely recommend an immunotherapy drug as a first-line treatment. This means you get an immunotherapy drug before any other treatment. You may also receive chemotherapy at the same time. 

If you have some expression of PD-L1, but less than 50%, your doctor may recommend a combination of immunotherapy and chemotherapy. Ask your doctor about your PD-L1 levels, any other biomarkers, and what they mean for your treatment options. 

In the video below, Dr. Edward Garon shares how PD-L1 levels can help determine treatments. 

Dr. Edward Garon explains the role of a patient’s PD-L1 levels in lung cancer treatment decision making.

Video transcript

How TMB Influences Treatment

Because immunotherapy helps the immune system find and attack cancer cells, some tumors with a higher TMB may be more likely to benefit from immunotherapy.  However, TMB is not a standalone decision-maker. A high TMB does not guarantee that immunotherapy will work, and a low TMB does not mean it won't. Doctors consider TMB alongside other factors, such as PD-L1 expression, other biomarker results, cancer type, stage, and the patient's overall health.  

Questions to Ask Your Doctor

Work with your doctor to discuss your goals and options each time you have to review and interpret test results to make a treatment decision. The three big questions to ask are:

  • What is the goal of this treatment?
  • What are the potential side effects?
  • What other options do I have?

Research is happening at a rapid pace, and your doctor should be up to date on the recommendations for your specific type of lung cancer. If you don’t feel comfortable with the answers you are receiving, do not hesitate to seek out a second opinion.

What to Do After Testing

Someone who has PD‑L1 expression can take several empowering steps to stay ahead of their care. These are general medical information steps, not personal medical directives, and it’s important to work closely with a qualified healthcare professional for decisions about diagnosis or treatment. 

Understanding whether your PD‑L1 and TMB levels are high, low, or in between helps you and your team decide how immunotherapy may fit into your treatment plan. 

Different PD‑L1 and TMB levels can open the door to different approaches, such as immunotherapy alone or in combination with chemotherapy; your team can explain which options make sense for your situation. 

Keeping notes on symptoms, side effects, or changes in how you feel helps your care team support you, adjust treatment if needed, and make sure your care aligns with your goals and preferences. 

Patient Support & Resources

Lung cancer research can move at a rapid pace. Always speak with your doctor about the most up-to-date treatment guidelines.

Page last updated: August 19, 2026

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