Immunotherapy is a type of cancer therapy that harnesses your immune system to fight cancer more effectively. People with breast cancer may use immunotherapy as part of their treatment plan.

Immunotherapy is mainly used to treat triple-negative breast cancer (TNBC). Your doctor may combine this treatment with chemotherapy either before or after surgery. Understanding how immunotherapy works and what to expect can help you feel more confident and prepared.

What Is Immunotherapy?

Immunotherapy is one of the most significant advances in cancer treatment in recent years. It boosts your immune system to fight and destroy cancer cells. The immune system is your body’s defense system that protects you from disease and infection. This complex system keeps track of what belongs in your body and recognizes foreign invaders like bacteria and viruses.

Cancer cells escape the body’s immune defenses to grow out of control. They can escape in a few ways:

• Some cancer cells still look like “normal” cells, letting them hide from the immune system.
• Certain cancers make substances that stop the immune system from finding them.
• The immune system may be able to find cancer cells, but it isn’t strong enough to destroy them.

Monoclonal Antibody Drugs as Immunotherapy

Breast cancer cells can sometimes suppress the immune response to avoid being attacked. Immunotherapy drugs can help the immune system overcome these actions.

Antibodies are specialized proteins that recognize certain patterns (antigens) on cells. Researchers have lab-engineered antibodies specially designed to alter the immune system so it can better combat cancer.

Monoclonal antibodies are a type of cancer immunotherapy that targets one specific protein. Some of these antibodies are considered targeted therapy. This is because they target a specific cancer cell protein to stop its function. Monoclonal antibodies that engage the immune system are considered immunotherapy.

How Is Immunotherapy Different From Chemotherapy?

Chemotherapy drugs usually target any cells in the body that grow quickly. Cancer cells typically grow fast, making them good targets for chemotherapy drugs. However, these drugs can’t tell the difference between fast-growing healthy cells — such as skin cells — and cancer cells. This means that normal, healthy cells are also damaged by chemotherapy (which is why you could lose your hair or get mouth sores while undergoing chemotherapy).

Unlike chemotherapy, immunotherapy doesn’t target fast-growing cells. Instead, it changes how a person’s immune system works. These changes help immune cells work harder to find cancer cells and kill or stop them from growing. Immunotherapy still comes with side effects, but they’re usually milder than the side effects of chemotherapy.

Types of Immunotherapy for Breast Cancer

Immunotherapy for triple-negative breast cancer blocks the proteins that breast cancer cells use to hide from the immune system. These drugs are also known as immune checkpoint inhibitors (ICIs).

To date, the U.S. Food and Drug Administration (FDA) has approved one class of immunotherapy to treat breast cancer. These medications are known as PD-1 inhibitors.

There are also several clinical trials underway to find other immunotherapies for treating breast cancer. Researchers use these large clinical studies to determine whether new drugs are safe and effective.

PD-1 Inhibitors

T cells are specialized immune cells that protect your body from infections. PD-1 is a checkpoint protein found on the outside of T cells. It interacts with another protein (PD-L1) to “turn off” the T cell. This prevents the immune system from attacking other healthy cells in the body.

PD-L1 is normally found on healthy, noncancerous cells. Some tumor cells also make the PD-L1 protein, which enables them to hide from T cell attacks.

Researchers have developed monoclonal antibodies or ICIs that block the PD-1 protein. Since PD-1 can’t interact with PD-L1, the T cell stays active. This means that T cells can recognize and attack cancer cells.

Pembrolizumab (Keytruda) is a PD-1 inhibitor that's FDA-approved to treat TNBC. Dostarlimab (Jemperli) is another PD-1 inhibitor. The FDA has approved dostarlimab-gxly to treat tumors with specific genetic changes (mutations). This medication is an immunotherapy for metastatic breast cancer and other metastatic cancers. “Metastatic” refers to cancer that has spread away from the original tumor site.

TNBC tumors usually make high levels of PD-L1 proteins. Before you start taking a PD-1 inhibitor, your doctor may order tests to see if your cancer cells have PD-L1.

Immunotherapies Under Study

Cancer immunotherapy is a relatively new area of study for breast cancer treatment. In clinical trials, scientists are investigating new treatments involving immune checkpoints — such as other PD-1 inhibitors and PD-L1 inhibitors. Nivolumab is one PD-1 inhibitor that is currently in a clinical trial for breast cancer treatment.

Vaccines are also a form of immunotherapy. You probably think of vaccines as something you get to avoid becoming sick. However, a cancer vaccine could help people who already have cancer. Scientists are working on developing a vaccine that can activate T cells to attack breast cancer tumors.

Talk to your doctor if you’re interested in participating in a clinical study for breast cancer treatment. They can help you find a trial focused on your type of breast cancer that you may be eligible to join.

When Is Immunotherapy for Breast Cancer Used?

Most breast cancer treatments work by blocking:

• Estrogen receptors
• Progesterone receptors
• HER2 proteins

Immunotherapies work best for advanced TNBC because these tumors don’t have any hormone receptors and they don’t make much HER2 protein.

Pembrolizumab for Breast Cancer

Pembrolizumab can be used along with chemotherapy to treat TNBC. The FDA has approved pembrolizumab for use:

• Before chemotherapy, known as neoadjuvant treatment
• After chemotherapy, known as adjuvant treatment

These treatments work best for people with recurrent TNBC that can’t be removed with surgery. You may also use pembrolizumab with chemotherapy if you have metastatic TNBC.

Dostarlimab-Gxly for Breast Cancer

Doctors prescribe dostarlimab to treat advanced-stage breast cancer that’s grown during or after other treatments. Dostarlimab treats people with specific genetic changes known as mismatch repair deficiencies (dMMRs). Your doctor will look for these tumor changes using an FDA-approved test.

Unlike pembrolizumab, dostarlimab is given on its own as a single agent. It isn’t combined with chemotherapy to treat breast cancer.

Side Effects of Immunotherapy for Breast Cancer

TNBC immunotherapy drugs can cause many side effects, depending on the type of treatment you are taking and the dose. Talk to your health care team about ways to prevent or treat your side effects.

Common Side Effects of Immunotherapies

The most common side effects of pembrolizumab include:

• Tiredness
• Cough
• Nausea
• Rash
• Itchiness
• Decreased appetite
• Muscle pain
• Constipation
• Diarrhea

Common side effects of dostarlimab include:

• Diarrhea
• Constipation
• Nausea and vomiting
• Anemia (low levels of red blood cells)
• Weakness and fatigue

Infusion and Allergic Reactions

Immunotherapies are given by infusion into a vein. Some people experience infusion reactions, which can feel like allergic reactions. Other possible side effects include:

• High fever
• Facial flushing or discoloration
• Chills
• Rash
• Dizziness
• Itchiness
• Breathing difficulties

You can also experience autoimmune reactions if the immunotherapy makes your immune system attack healthy cells. This can lead to serious or life-threatening problems in many organs, including:

• Lungs
• Kidneys
• Liver
• Intestines
• Glands that make hormones

Talk to your health care team if you experience any side effects of your immunotherapy treatment.

What’s the Success Rate of Immunotherapy for Breast Cancer?

Researchers have performed several clinical trials to understand how well immunotherapies treat TNBC. These studies have shown that immunotherapies can help people with breast cancer live longer.

For example, one trial found that pembrolizumab with chemotherapy improves overall survival with advanced TNBC. This means that on average, the study participants on pembrolizumab lived longer. The same study also found people treated with pembrolizumab and chemotherapy didn’t see their cancer grow worse for an average of 9.7 months. Cancer grew worse for people receiving only chemotherapy after 5.6 months, on average.

Clinical trials are also studying how well dostarlimab works for breast cancer. One study is looking at dostarlimab with chemotherapy for early-stage cancer. Another is investigating targeted therapy with dostarlimab. These studies haven’t finished yet, so it may be some time before we know how effective dostarlimab combination treatments are.

Talk With Others Who Understand

MyBCTeam is the social network for people with breast cancer and their loved ones. On MyBCTeam, more than 74,000 members come together to ask questions, give advice, and share their stories with others who understand life with breast cancer.

Have you received immunotherapy treatment for breast cancer? Share your experiences in the comments below, or start a conversation by posting on your Activities page.