Immunotherapy for Breast Cancer

April 10, 2025

This page was reviewed under our medical and editorial policy by Susan Yost, Ph.D., staff scientist, Department of Medical Oncology & Therapeutics Research, City of Hope^® Cancer Center Duarte

Immunotherapy is a type of cancer treatment that works by increasing or decreasing the activity of a person’s immune system to fight cancer. It may be recommended for certain types of breast cancer.

What Is Immunotherapy for Breast Cancer?

Immunotherapy is a type of biological therapy that helps a person’s own immune system find and destroy cancer cells. Biological therapies are made from living things, like cells, antibodies and viruses, and help fight cancer. One of the main immunotherapies for breast cancer, Keytruda^® (pembrolizumab), is made of antibodies, a normal protein found in the immune system that finds and attacks abnormal cells.

While treatment plans vary from patient to patient, some patients with metastatic breast cancer may benefit from an immunotherapy medicine specifically approved to treat their cancer.

Types of Immunotherapy for Breast Cancer

Advances in immunotherapy treatment for breast cancer are in the pipeline as researchers continue to study their role in treating breast cancer and extending survival. Immunotherapy may be a component of a breast cancer treatment plan, particularly for some patients with triple-negative breast cancer.

Immune checkpoint inhibitors, a type of monoclonal antibody, is a type of immunotherapy used in breast cancer that directs the immune system to destroy cancer. Other monoclonal antibodies work more directly inside breast cancer cells to destroy them and also sometimes boost the immune system. They are not strictly considered immunotherapy. These other monoclonal antibodies have slightly different jobs at the site of the cancer cell and are often considered targeted therapies for breast cancer, meaning that they target specific molecules that cancer cells rely on to survive and spread.

Immune Checkpoint Inhibitors

Immune checkpoint inhibitors work to help immune system cells stay active in order to find and destroy cancer cells. Tumor cells can make a normal protein that tells the immune system to leave it alone. These are called checkpoint proteins. These checkpoint proteins help cancer to hide from the immune system’s T cells by telling the T cells to turn off.

Immune checkpoint inhibitors block the checkpoint proteins from binding to T cells, which allows the body’s T cells to destroy the cancer cells.

Keytruda^® targets a protein on the T cells known as PD-1, which normally stops T cells from attacking other cells in the body. Blocking PD-1 lets the T cells attack the breast cancer cells. Keytruda® may be used along with chemotherapy to treat triple-negative breast cancer.

Keytruda^® is given as an intravenous infusion once every three or six weeks. The length of treatment may vary from 24 weeks to two years based on a patient’s response to treatment and side effects.

Risks and Side Effects

Side effects of immunotherapy for breast cancer vary by the treatment type, the therapies given along with it and the length of treatment. Side effects differ from patient to patient.

Drugs given intravenously may cause infusion-related reactions, which are similar to allergic reactions. Symptoms of an infusion-related reaction may include:

• Chills
• Fever
• Facial flushing
• Itchiness or rash
• Dizziness
• Breathing problems and wheezing

Side effects of checkpoint inhibitors, such as Keytruda^®, may include:

• Cough
• Fatigue
• Skin rashes
• Decreased appetite
• Nausea, diarrhea or constipation

Because these drugs allow the body’s immune system to work without usual limits, serious or life-threatening problems may occur. These may include problems with the liver, lungs, intestines, kidneys, glands that produce hormones and other organs.

Typically, monoclonal antibodies, such as immune checkpoint inhibitors, have fewer side effects than other treatments for breast cancer.

Patients receiving immunotherapy treatment should report any new side effects to their health care team right away. In some cases, treatments may need to be stopped and other drugs, such as steroids, may be recommended to help balance the immune response.

Breast Cancer Immunotherapy at City of Hope

At City of Hope, members of the care team work with patients to determine the optimal treatment options for breast cancer. If immunotherpy is an option for a particular patient, the care team will share the available therapies, as well as their risks and side effects.