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Immunotherapy for Breast Cancer
Immunotherapy is part of treatment for some types of breast cancer.
Immunotherapy uses medicines to boost your immune system so it can better recognize and destroy cancer cells. Most immunotherapy works on specific proteins in the immune system. The side effects of these medicines are different from chemotherapy.
Some immunotherapy medicines, such as monoclonal antibodies, work in more than one way to control cancer cells. These may also be considered targeted therapy because they block a specific protein on the cancer cell to keep it from growing.
Immune checkpoint inhibitors for breast cancer
An important part of your immune system is its ability to keep itself from attacking normal cells in your body. To do this, it uses “checkpoint” proteins on immune cells. These proteins act like switches that need to be turned on or off to start an immune response.
Breast cancer cells sometimes use these checkpoints to avoid being attacked by the immune system. Medicines that target these checkpoints are called immune checkpoint inhibitors. They help restore the body’s immune response against breast cancer cells.
PD-1 inhibitors
PD-1 is a protein on immune system T cells that normally helps keep them from attacking other cells in the body. By blocking PD-1, these medicines boost the immune response against breast cancer cells. This can often shrink tumors.
Pembrolizumab (Keytruda)
Pembrolizumab (Keytruda) is a PD-1 inhibitor that can be used with chemotherapy to treat triple-negative breast cancer:
- Before and after surgery for early-stage cancers
- If the cancer comes back (recurs) locally but cannot be removed by surgery
- If the cancer has spread to other parts of the body
This medicine can be injected under the skin (subcutaneous injection) or put into a vein through an IV. It is typically given every 3 weeks or every 6 weeks. Your doctor might test your cancer cells for the PD-L1 protein to show that the cancer is more likely to respond to treatment with pembrolizumab.
Possible side effects
Common side effects of immune checkpoint inhibitors include:
- Fatigue
- Cough
- Nausea
- Skin rash
- Constipation or diarrhea
More serious side effects that happen less often include:
- Infusion reactions. This is like an allergic reaction. It can happen while getting these medicines and can include fever, chills, flushing of the face, rash, itchy skin, dizziness, wheezing, and trouble breathing. Tell your treatment team right away if you have any of these symptoms during your infusion.
- Autoimmune reactions. These medicines remove one of the protections on the body's immune system. Sometimes the immune system starts attacking other parts of the body. This can cause serious or even life-threatening problems in the lungs, intestines, liver, hormone-making glands, kidneys, or other organs.
It’s very important to tell your healthcare team right away if you have any new side effects during or after treatment with these medicines. If you have serious side effects, you might need to stop treatment and take high doses of corticosteroids to suppress your immune system.
More information about immunotherapy
To learn more about how drugs that work on the immune system are used to treat cancer, see Cancer Immunotherapy.
To learn about some of the side effects listed here and how to manage them, see Managing Cancer-related Side Effects.
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- References
Developed by the American Cancer Society medical and editorial content team with medical review and contribution by the American Society of Clinical Oncology (ASCO).
Anders CK and Carey LA. ER/PR negative, HER2-negative (triple-negative) breast cancer. In Vora SR, ed. UpToDate. Waltham, Mass.: UpToDate, 2025. https://www.uptodate.com. Last updated July 21, 2021. Accessed August 13, 2026.
Cortes J, Rugo HS, Cescon DW, et al. Pembrolizumab plus Chemotherapy in Triple-Negative Breast Cancer. N Engl J Med. 2022 Jul 21;387(3):217-226.
Jagsi R, King TA, Lehman C, Morrow M, Harris JR, Burstein HJ. Chapter 79: Malignant Tumors of the Breast. In: DeVita VT, Lawrence TS, Rosenberg SA, eds. DeVita, Hellman, and Rosenberg's Cancer: Principles and Practice of Oncology. 12th ed. Philadelphia, Pa: Lippincott Williams & Wilkins; 2023.
Korde LA, Somerfield MR, Carey LA, et al. Neoadjuvant Chemotherapy, Endocrine Therapy, and Targeted Therapy for Breast Cancer: ASCO Guideline. J Clin Oncol. 2021;39(13):1485-1505.
National Comprehensive Cancer Network (NCCN). Practice Guidelines in Oncology: Breast Cancer. Version 2.2026. Accessed at https://www.nccn.org/professionals/physician_gls/pdf/breast.pdf on May 4, 2026.
Last Revised: July 9, 2026
American Cancer Society medical information is copyrighted material. For reprint requests, please see our Content Usage Policy.
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