Immunotherapy Biomarkers

Summary: This resource provides an overview of the various cancer biomarkers used to predict response to immunotherapy.

By JAX Clinical Education | May 2026

To identify candidates for immunotherapy, multiple biomarkers may be useful for clinicians and patients, including PD-L1, microsatellite instability (MSI), mismatch repair deficiency (dMMR), and tumor mutation burden (TMB).

While these biomarkers can help identify patients who may benefit from immunotherapy, they are surrogate indicators of response to immunotherapy. They are not 100% predictive of a favorable response to any single agent, or immunotherapies in general.

Patients with positive biomarkers may not respond to immunotherapy
Patients with negative biomarkers may still respond on immunotherapy

Not all biomarkers are included on every test; multiple tests may need to be requested.

Biomarker	How it is measured	How it works
Tumor mutation burden (TMB)	Assesses DNA to measure of the number of mutations in the tumor	Some mutations in cancer cells result in modified cell surface proteins, called neoantigens. Neoantigens are thought to be targeted by the immune system to produce an antitumor response. High TMB results in increased neoantigens on the cell surface, which as some experts believe, makes it more likely that the immune system will differentiate the cancer cell from noncancer cells.
Microsatellite Instability (MSI)	Assesses DNA to identify if the tumor has an abnormal number of microsatellites	MSI-high tumors have a defective DNA repair mechanism, creating more genomic instability, which may make them more susceptible to immunotherapy.
Mismatch repair deficiency (dMMR)	Assesses expression of MMR proteins using immunohistochemistry (IHC)	Tumors with MMR have compromised cellular DNA repair abilities and may be more susceptible to immunotherapy.
PD-L1	Assesses expression of PD-L1 proteins using immunohistochemistry (IHC)	PD-L1 binds with PD-1, a cell surface protein expressed on activated T cells that acts as a checkpoint inhibitor. Cancer cells positive for PD-L1 may respond to immunotherapy, specifically treatment with PD-L1/PD-1 inhibitors.

Learn More

Explore Cancer Biomarker Testing (CME|CNE). Learn about benefits, limitations, and challenges of using large biomarker tests.

ESMO Factsheets on Biomarkers (Oncology Pro). Factsheets about common biomarkers that discuss prognostic and predictive value, testing recommendations, and patient indications.

References

Wang SL, Chan TA. Navigating established and emerging biomarkers for immune checkpoint inhibitor therapy. Cancer Cell. 2025;43(4):641-664. doi:10.1016/j.ccell.2025.03.006

Disclaimer

All information in this resource is provided for educational purposes only.