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Updated on April 7, 2025
Biomarker testing looks for the presence of certain biological molecules on cancer cells. When certain biomarkers are present in certain levels, it gives healthcare providers an idea of the processes the cancer is using to grow and spread—and predict what therapies might be most effective in treating that cancer. Certain anti-cancer treatments work by disrupting these processes.
PD-1 and PD-L1 proteins are one example of biomarkers that are found in some cancers. Here we look at the role of these proteins in the body, how cancer cells use these proteins to fuel their growth, and how certain anti-cancer drugs target these proteins.
Immune checkpoint inhibitors
The immune system attacks and destroys cells, pathogens, and foreign substances that enter the body. To keep the immune system from damaging healthy cells, the body also contains proteins called immune checkpoints.
PD-1 and PD-L1 are immune checkpoint inhibitors. Together, they form what is called the PD-1/PD-L1 pathway.
- PD-1 is a protein found on immune cells called T cells.
- PD-L1 is a protein found on normal healthy cells.
- When PD-1 binds to PD-L1, it stops the immune system from attacking the normal healthy cells.
Keep in mind that this is a simplified explanation of a complex biological process.
PD-L1 on cancer cells
Some cancer cells produce high amounts of PD-L1. These high levels of PD-L1 essentially act as a disguise. They let the cancerous cells appear normal and avoid attack when they encounter T cells. This allows the cancerous cells to continue to grow and proliferate.
PD-1/PD-L1 inhibitors
Some anti-cancer drugs work by disrupting the PD-1/PD-L1 pathway. These drugs are called PD-1 inhibitors or PD-L1 inhibitors, depending on which protein they act on. When this immune checkpoint process is disrupted, T cells will attack the cancer cells.
PD-1 and PD-L1 inhibitors are categorized as immunotherapies. That means they work by helping the body’s immune system find and eliminate cancer. These drugs may be prescribed alone, or in combination with other cancer therapies, such as chemotherapy.
Your healthcare providers may order tests to measure the levels of PD-L1. This test involves taking a biopsy (sample) of the cancer cells, which is then examined in a lab. PD-L1 levels are one piece of information that your healthcare providers will use to help predict what cancer treatments may be effective.
Remember that every case of cancer is different. The best source of information about your diagnosis is your healthcare team.
